BTZS + Modern Incident Meter w/ Digital Readout [Archive]

Ken Lee

6-Mar-2012, 20:43

Beyond The Zone System, 4th Edition, pp. 136, paragraph 2:

"1. Take the bright light (high) reading.
2. Take the shadow (low) reading.
3. Subtract the low reading from the high reading (in stops).
4. Add that difference to 5 (the standard minimum range) to find the total subject [brightness] range (SBR) in stops.
5. Consult the EFS chart to find the appropriate film speed, and set it into your meter dial.
6. With the meter pointer set on the shadow (low) reading, select the camera settings, and make the exposure. Record the SBR number.
7. Consult the developing chart to find the development time that's appropriate for the SBR, and develop accordingly."
Those instructions likely refer to meters whose display is a dial, not the more modern meters which give results in numbers.

Would it be correct to re-state numbers 5 - 6 as follows ?

5. Consult the EFS chart for your film/developer combination, find the appropriate film speed for the specified SBR, and set your light meter to that speed.
6. Take the shadow (low) reading again, and expose with the settings recommended by the meter. Record the SBR number.

This may all be obvious to BTZS afficionados, but as a newcomer, I am confused with the nomenclature - particularly because my current meter (Pentax Digital Spot) reads in LV, while my ancient Incident meter has a dial, and gives results in terms of EV.

I'm also aware that the ExpoDev software automates much of this, and incorporates additional variables like flare, filter factor, bellows extension, reciprocity, etc - but I'm trying to grasp the core principal here.

Thank you :)

mdm

7-Mar-2012, 00:19

I can change iso on my cheap digital meter without loosing the shadow reading. It just modifies the exposure recomendations. Sekonic L308S off ebay.

Shen45

7-Mar-2012, 02:02

Ken buy yourself the Palm pilot and theExpoDev software. It is all very inexpensive. You can get a small tool from the ViewCamera store called a powerdial which is a calculator for both incident and spot readings.
Failing that if you are on Skype someone who is actually a user of the system will be able to help. Heck "pester" :) Sandy he probably has as great or greater working knowledge of BTZS as anyone. Only those that use the system actually understand the system. On our forum here you will get 90% answers from people who have not any idea about BTZS and just in their naivety think it is the same as the ZS, which it is not.

Steve

Ken Lee

7-Mar-2012, 04:29

Thanks for the recommendations. I mentioned in my post that I am aware of the ExpoDev software, but I'm trying to grasp the fundamental concept. Meters with dials often behave differently than meters with numeric readouts, and explanations can be... ambiguous.

I actually have a Power Dial, and find that the exposures it recommends are at odds with what Phil Davis recommends on pp. 136 paragraph 2 of the latest edition of his book. In Appendix 5, he gives some instructions about its use, but there are some questions about which ISO to set, which remain unanswered. I get the impression that he was rushed by one reason or another, when adding that section to the book. For example, he tells you to use the box speed of your film - except 250 when shooting TXT, and 80 when shooting FP4. He doesn't explain why those films would be handled that way - and not others. Many people shoot those films at lower-than-box speed of course, but it's surprisingly inconsistent, considering how earnest and meticulous the bulk of his writing are.

jcoldslabs

7-Mar-2012, 04:55

Shen45

7-Mar-2012, 04:57

Ken with the systen I didn't really get a handle on it until I shot and processed a couple of negatives. I do admit to going virtually straight away to the ExpoDev because of the many calculations it does for you. I have the full kit - the WinPlotter program and the ExpoDev. I do all my own testing and also test film occassionally for friend here in Australia. Me personally, I cannot be bothered now to "understand" the system [I do] because it is absolutely flawless. I still suggest you have a one on one chat with someone like Sandy or one of the others in the US who is a full user. A half hour phone call would probably cost you about $1.

Mark Barendt

7-Mar-2012, 05:02

I am not an afficionado but it seems that the intent of 5&6 is simply to place the shadows. (Shooting to the shadows.)

There appears to be an adjustment to the EI, which makes sense given the change in process, but then there is another offset thrown in for readings in shadow.

The language used is confusing and the double offset (for EI then shadow) seems overly complicated too.

Shen45

7-Mar-2012, 05:11

Ken (or anyone),

I am not steeped in BTZS methodology, but I have a basic (and probably stupid) question regarding steps 1-4 in the opening post. I use a Pentax Digital Spotmeter and to find the SBR I just meter the brightest spot where I want detail and the darkest spot I want detail. The difference in stops is the SBR--or so I have assumed.

Following the above steps I am imagine this: shadows = EV 8; highlights = EV 13. Difference = five stops. Add that to 5 and you get 10 for the SBR. Huh?

Feel free to smack me upside the head and tell me to get Phil's book, but I am curious as to why it seems so complicated.

Also, Ken, I thought the Pentax meter's LED viewfinder display was in EV numbers. Is that not the case?

:confused:

Jonathan

Hi Jonathon,

For a start BTZS is not the zone system as most apply it. I just plugged you figures into my Palm with ExpoDev and we first need to establish at what "zone" your brightest highlight falls. Phil suggested 3 and 7 so going by his recommendation your metering gives an SBR of 8.8 with an exposure of 1/2 sec @ f11 1/3 developed for 5:27 -- however if you are basing your range on 3 and 8 then the sbr is 7 with 1/2 second @ f 11 2/3 processed for 8:23. --- Figures based on my film test.

Edit : Meant to add that the algorithim used for incident and spot metering seem to be different but give the same results for a scene metered correctly.

jcoldslabs

7-Mar-2012, 05:14

Steve,

Thanks for the quick calculations on my behalf. I wasn't expecting a free tutorial in BTZS, but your reply helps my conceptual understanding.

Jonathan

EDIT: I've still got my old Palm III lying around. You mean it can still be used for something?

Mark Barendt

7-Mar-2012, 05:28

Ken (or anyone),

I am not steeped in BTZS methodology, but I have a basic (and probably stupid) question regarding steps 1-4 in the opening post. I use a Pentax Digital Spotmeter and to find the SBR I just meter the brightest spot where I want detail and the darkest spot I want detail. The difference in stops is the SBR--or so I have assumed.

Following the above steps I am imagine this: shadows = EV 8; highlights = EV 13. Difference = five stops. Add that to 5 and you get 10 for the SBR. Huh?

Feel free to smack me upside the head and tell me to get Phil's book, but I am curious as to why it seems so complicated.

Also, Ken, I thought the Pentax meter's LED viewfinder display was in EV numbers. Is that not the case?

:confused:

Jonathan

Spot meter readings, high minus low, gives you a real measured SBR.

Incident metering doesn't read SBR directly, because it doesn't read the reflective brightness value of specific points like the darkest shadow, it measures a much larger portion of the scene, so SBR has to be inferred by adding the 5-stop constant to the difference.

Ken Lee

7-Mar-2012, 05:51

"Following the above steps I am imagine this: shadows = EV 8; highlights = EV 13."

Although reflective and incident meters each have pitfalls, one of the core value propositions of incident metering, is that we don't have to decide which subjects belong in which "Zones". The Zone System facilitates Pre-Visualization, but the flip-side of that, is that we often take our best guess about what belongs where.

That a B&W viewing filter is popular with Zone System users (myself included, after 40 years) is revealing. For example, see that pumpkin over there ? It kinda looks like Zone IV to me, but is it ? Should it be ?

Shen45

7-Mar-2012, 06:29

Shen45

7-Mar-2012, 06:34

Sorry about the deleted post. Ken your observation re incident and BTZS are spot on. With spot metering you can meter a section of your scene and put that ev into the a test area of the ExpoDev and it will give you a "zone" that the film you have tested will render it on the particular paper you are using. Quite useful.

jcoldslabs

7-Mar-2012, 06:42

Incident vs. spot. That makes sense.

Jonathan

Ken Lee

7-Mar-2012, 06:51

I have already purchased Plotter program, and am waiting for the iPhone version of ExpoDev to come out.

I intend to measure my scanner and use it in place of "paper".

While it's great that both systems are supported, if I switch to BTZS I will work within its parameters instead. It's hard to teach an old dog new tricks, but it's good to keep... stretching.

sanking

7-Mar-2012, 07:50

Ken,

I believe you own the 3rd edition of Beyond the Zone System. If that is true, please read carefully pp. 111-114, which covers The Standard Gray Card. Some of this may seem a bit obtuse, but the basic issue is that the 18% gray card (and the 18% light transmitted by the incident cone) is not really middle gray as used by ANSI standards for meter calibration of a seven stop, or log 2.1 range. Apparently the use of the gray card ordinated in the studio where the luminance range of copy subjects is 5 stops, or log 1.5.

Sandy

cowanw

7-Mar-2012, 08:52

read here
http://www.apug.org/forums/archive/index.php/t-36416.html
an amazing thread on many levels but if you keep at it a lot of insight into the different way people think on these things

Ken (or anyone),

I am not steeped in BTZS methodology, but I have a basic (and probably stupid) question regarding steps 1-4 in the opening post. I use a Pentax Digital Spotmeter and to find the SBR I just meter the brightest spot where I want detail and the darkest spot I want detail. The difference in stops is the SBR--or so I have assumed.

Following the above steps I am imagine this: shadows = EV 8; highlights = EV 13. Difference = five stops. Add that to 5 and you get 10 for the SBR. Huh?

Feel free to smack me upside the head and tell me to get Phil's book, but I am curious as to why it seems so complicated.

Also, Ken, I thought the Pentax meter's LED viewfinder display was in EV numbers. Is that not the case?

:confused:

Jonathan

Ken Lee

7-Mar-2012, 08:59

I believe you own the 3rd edition of Beyond the Zone System. If that is true, please read carefully pp. 111-114, which covers The Standard Gray Card.

Thanks - I now have the latest edition as well as the 3rd edition - just to make sure I don't miss anything. Obtuse is a good word :)

There appear to be 3 basic principals at work. They intersect as follows:

The first principle is that exposure and development time often need to be adjusted to accommodate subject brightness range, and film speed varies with development time. So when taking a photo, it's best to measure the SBR first, set film speed accordingly, and develop accordingly.

The second principle is that 18% is a traditional number, but not the correct midpoint for subject brightness. It's actually 12.5%, or even 9% if we do the arithmetic. Therefore, metering the reflection off an 18% gray card will result in 1/2 stop underexposure if we consider 12.5% to be the correct average gray. If we use 9%, then we're underexposing by a full stop. Since incident meters are also based on the (wrong) 18% standard, they also give us readings which result in 1/2 stop underexposure (or 1 stop, if we use the 9% value)... unless we work around the problem.

How we work around the problem, is the part that gets obtuse :-)

The third principle is that we must base our exposure on the shadow (low) reading, because it's critical with b&w negative film. ("Expose for the shadows, develop for the highlights").

The obtuse part is that simply metering for the shadows would normally result in overexposure, since shadows need to be dark. However, we know that the incident meter is going to give us a reading by which we will be under-exposing by 1 stop. So it ends up OK in the end.

Is that it, in a nutshell ?

Mark Barendt

7-Mar-2012, 09:28

Ken Lee

7-Mar-2012, 09:37

Ken,

Incident meters aren't necessarily calibrated to 18%. My understanding is that they are closer to 12%. The standard though is a range not an absolute number, manufactures can vary their calibration within the range.

The other factor at play is EI. Our personal testing to get to an EI (a personal film speed to meter calibration) is not normally done to ISO or ANSI laboratory standards and very posibly not even using the same benchmarks for speed point.

Personally in find no underexposure when using my incident meters at box speed on any film. Granted my observation is as subjective as anybody's but that's pretty much the point I'm trying to make.

Beyond the Zone System, Fourth Edition, page 116, paragraph 2 (emphasis mine):

"The milky plastic dome accepts light from a very wide area - approaching a solid angular field of 180 degrees - and transmits approximately 18% of the incident light to the cell underneath so that the meter provides the equivalent of a three-dimensional gray card reading...

...Neither luminance meter nor incident meters can provide direct, accurate exposure data for most subject conditions. If you want precise data, you must always use special metering techniques or modify the meter's recommendations, or both."

Page 118, paragraph 2 (emphasis mine):

"Because the incident meter's cell always sees 18% gray, it will do the same thing if you follow the meter's recommendation without modification."

Page 132, paragraph 2:

"... basing camera settings on a single shadow reading will typically result in overexposure of about 1 stop."

Page 134, paragraph 4 (emphasis mine):

"Next consult the effective film speed chart (figure 9-10a) to find the film speed number appropriate for the SBR, and set it into the meter dial in place of the official ISO film speed. Notice that these film speeds seem exaggerated: they are, in fact, just double the normal film speeds. As explained earlier, this is done deliberately to compensate for the 1-stop overexposure that normally results when the camera settings are based on the low-light incident reading."

So, relying on an 18% meter gives 1 stop underexposure, but reading the shadows gives 1 stop overexposure. Then, by using an effecitve film speed appropriate for the SBR (derived from careful testing), we get the right exposure. Then we develop to match the SBR. It sounds perfectly coherent.

If all of that works together, then the only part I don't follow, is his suggestion that effective film speeds have been doubled on purpose. I thought that EFS is determined through testing, and is not tied to box speed, or boosted according to any "canned" value whatsoever. In fact, nowhere in his instructions on incident metering, do I see a recommendation to use box speeds or any arbitrary correction factor. That would seem contradictory to the whole spirit of individual testing and calibration.

It may be that in a book of this size, no author can keep track of all the changes made through 4 editions, and the result is that a few sections of the book don't agree with one another. It wouldn't be the first time :)

sanking

7-Mar-2012, 10:24

"The milky plastic dome accepts light from a very wide area - approaching a solid angular field of 180 degrees - and transmits approximately 18% of the incident light to the cell underneath so that the meter provides the equivalent of a three-dimensional gray card reading..."

Ken,

The plastic dome transmits approximately 18% of the incident light to the cell, that is why it gives a similar reading to a reflected light reading with an 18% gray card.

But the internal calibration of meters is not for 18%, but as Mark indicates, 12% or 12.5%. I believe that information is also in BTZS in the pages I mentioned. That is part of the reason why we have to adjust exposure with an incident reading for shadow and highlight readings with B&W film.

Sandy

Mark Barendt

7-Mar-2012, 11:22

Ken,

First, the principles of setting exposure, etcetera, put forth in the BTZS books is not the same as the ISO standard. Two different animals. Manufacturers don't have to use domes that transmit a certain percentage of light.

Second, spot metering the darkest spot we want detail in and incident metering in that same light should normally provide very different readings.

Example, a groom wearing a black tux on a sunny day with the afternoon sun behind him. An incident meter reading taken at His chest is probably going to be about f/4 @ 1/125 for ISO 125 film, a spot reading on the black fabric might read f/4 @ 1/8 for ISO 125.

Ken Lee

7-Mar-2012, 12:15

Yes Mark, you're certainly right.

Part of the problem here is that with technical matters, it can often take a lot of words to describe exactly what we mean. "Taking a reading in the shadows" is a vague statement. "Taking an incident reading in the shadows" is still a vague statement. Of course, if we know what the writer means already, it's clear, and we're puzzled that others don't.

That's why I started this thread, with my question about what Phil meant when he wrote so-and-so about using a meter.

Perhaps I should take the good advice offered, and perform my own tests. To that end I have just purchased a nice meter that will do both Spot and Incident readings. The dome on my analog Sekonic meter (which I bought as a backup for travel because it's so tiny) is so small that unless you hold it just right, the edge of the meter covers the dome. When the real meter arrives, I'll be testing in earnest, and hopefully all will be revealed.

Many thanks for your help.

Bill Burk

7-Mar-2012, 14:12

The second principle is that 18% is a traditional number, but not the correct midpoint for subject brightness. It's actually 12.5%, or even 9% if we do the arithmetic. Therefore, metering the reflection off an 18% gray card will result in 1/2 stop underexposure if we consider 12.5% to be the correct average gray. If we use 9%, then we're underexposing by a full stop. Since incident meters are also based on the (wrong) 18% standard, they also give us readings which result in 1/2 stop underexposure (or 1 stop, if we use the 9% value)... unless we work around the problem.

How we work around the problem, is the part that gets obtuse :-)

The third principle is that we must base our exposure on the shadow (low) reading, because it's critical with b&w negative film. ("Expose for the shadows, develop for the highlights").

The obtuse part is that simply metering for the shadows would normally result in overexposure, since shadows need to be dark. However, we know that the incident meter is going to give us a reading by which we will be under-exposing by 1 stop. So it ends up OK in the end.

I spent the past couple evenings reviewing all the urban legend sites about 18%.

I don't think you should worry about it. The meters aren't calibrated to 18%, not even the incident meters. They are trying to recommend the correct exposure. (I think our poster on a previous thread who did a test and found his specific meter calibrated at 18% may have found a meter that is calibrated to 18%, the folklore supports that can happen).

When you take the incident meter into the shade of your subject for BTZS, and use the EI for the SBR that the Power Dial or Expo-Dev recommends. You are properly exposing and developing your film. That's my take.

The urban legends can be updated at our leisure but I really don't think they enter into it unless you really take an 18% card into the field with you because - then - you have an 18% to adjust to whatever your meter is calibrated to.

By the way, has anybody ever made a "real" Power Dial? The one where you take slivers of masking paper and print paper and actually make a dial with gray wedges? Just curious, bet they are rarer than anything.

Ken Lee

7-Mar-2012, 14:30

When you take the incident meter into the shade of your subject for BTZS, and use the EI for the SBR that the Power Dial or Expo-Dev recommends. You are properly exposing and developing your film.

You are probably right, but inquiring minds want to know how and why, so that they can do the same thing on their own, armed with only a camera and light meter.

That's why my original post reads: "I'm also aware that the ExpoDev software automates much of this, and incorporates additional variables like flare, filter factor, bellows extension, reciprocity, etc - but I'm trying to grasp the core principal here. "

Bill Burk

7-Mar-2012, 15:11

You are probably right, but inquiring minds want to know how and why, so that they can do the same thing on their own, armed with only a camera and light meter.

That's why my original post reads: "I'm also aware that the ExpoDev software automates much of this, and incorporates additional variables like flare, filter factor, bellows extension, reciprocity, etc - but I'm trying to grasp the core principal here. "

Traditional Zone System gave you an EI that didn't vary whether you used N-2 or N or N+2 ignoring the "fact" you get "more" speed when you develop longer and less speed when you develop less.

BTZS took in that fact and gives you a "sliding EI" that tells you to use different meter EI according to the scene.

Did you get the core principle you wanted? I'd say it is to meter in the shady part of your important subject - (and yes, go back later after picking your EI and meter shadow again if the meter dial lost your first reading). This metering determines exposure and it's incident so what the meter says is what you should expose. It will give you good shadow detail even on something dark gray in shade.

Then incident meter in the full brightly lit part of your important subject. The difference in readings plus 5 is the subject brightness range. You don't use the reading here for exposure setting. Just for development.

Ken Lee

7-Mar-2012, 16:29

Yes, thank you :)

Stephen Benskin

7-Mar-2012, 17:13

Ken Lee

7-Mar-2012, 19:58

An easy way to determine the relative "average" reflectance is to divide the exposure constant of the reflection meter by the exposure constant of the incident meter. The basic standard is K = 1.16 cd/ft^2 / 12.5 cd/m^2 for a reflected exposure meter and C = 30 fc / 322 mc.

K / C = average reflectance

(1.16*pi) / 30 = 0.12

Let Average Reflectance = K/C
Where K = Exposure Meter = 1.16 candles per square foot (which is the same as 12.5 candles per meter squared) ?
and C = 30 foot candles (which is the same as 332 meter candles) ?

Then K/C = 1.16/30... where does PI come in please ?

What is the exposure constant of a meter ? What do we mean by "relative average reflectance" ? Could you explain these terms in a little more detail please ?

Thank you. It's wonderful to have such knowledgeable people on the forum.

Stephen Benskin

7-Mar-2012, 20:50

Let Average Reflectance = K/C
Where K = Exposure Meter = 1.16 candles per square foot (which is the same as 12.5 candles per meter squared) ?
and C = 30 foot candles (which is the same as 332 meter candles) ?

Then K/C = 1.16/30... where does PI come in please ?

Yes 12.5 is candles per meter squared and 332 is in meter candles if I have my units correct. You can use these values for the equation, but you still need to use pi. I like to use cd/ft^2 for K because it works with the calibration equation and I can invision the factor aspect of the K factor better using it. (see embedded page below)

pi is to convert cd/ft^2 to Footlamberts.

You can, of course, also use the average illuminance and the average luminance. (297 * pi) / 7681 = 0.12
Where do those numbers come from? Take f/16 squared and multiply it by the constants K = 1.16 and C = 30. That's why you can use the constants to determine the relative average reflectance.

What is the exposure constant of a meter ? What do we mean by "relative average reflectance" ? Could you explain these terms in a little more detail please ?

Meters don't see reflectance, but you can determine a reflectance that should balance results from the reflected meter to the incident meter under the same illuminance. It's relative.

What is the exposure constant of a meter?

In a nut shell, the constants can be considered a light loss factor that takes into consideration the characteristics of the exposure meter and the camera's optical system. A hand held meter doesn't see through the camera lens. While on the whole, the constants can be considered a light loss factor, it doesn't necessarily apply to all the variables involved in determining the constants.

You can find a detailed explanation of the constants at http://www.apug.org/forums/forum37/85217-k-factor-relevant-me-should-i-cancel-out.html

Here's an sample page from that discussion.

69757

Ken Lee

8-Mar-2012, 04:17

Meters don't see reflectance, but you can determine a reflectance that should balance results from the reflected meter to the incident meter under the same illuminance. It's relative.

In a nut shell, the constants can be considered a light loss factor that takes into consideration the characteristics of the exposure meter and the camera's optical system. A hand held meter doesn't see through the camera lens. While on the whole, the constants can be considered a light loss factor, it doesn't necessarily apply to all the variables involved in determining the constants.

And therefore 12.5% is what a gray card should reflect, if a reflectance meter is going to recommend the same exposure as an incident meter ?

Mark Barendt

8-Mar-2012, 05:22

And therefore 12.5% is what a gray card should reflect, if a reflectance meter is going to recommend the same exposure as an incident meter ?

Both types of meters would hopefully and directly (without any correction/offset) report the same EV if a 12.5% gray card was in use.

The only practical difference between using an incident meter and spot metering with any "known" target, is a mathematical offset.

A white card or black card or your palm can all be used just as accurately and provide exactly the same end result; different targets simply require their own offsets. That offset can be applied where ever its handy. It can be dialed into the meter (iso setting or exposure compensation setting adjusted) or done in your head.

The bigger problem with reflected readings matching incident is human. Our judgement of the orientation of the target and the like.

rdenney

8-Mar-2012, 07:05

Both types of meters would hopefully and directly (without any correction/offset) report the same EV if a 12.5% gray card was in use. ...
The bigger problem with reflected readings matching incident is human. Our judgement of the orientation of the target and the like.

It seems to me that a bigger problem still is that the light that reaches the camera, as measured by an incident meter, is an integration, while the values in the scene that are important to us might not integrate the same way. For example, with a back-lit subject, the light falling on the camera might integrate to a substantially larger value than the light coming from the subject. There is no guarantee that all the light falling on the camera, as measured using an incident meter, actually comes from the scene being photographed.

It seems to me that the point of the Zone System was to decide what scene values we want to fall on what visualized values. If we want to make sure we have detail in a shadow area, we meter that particular area and place it on, say, Zone III in the print. If a highlight in which we want detail falls beyond Zone VIII, then we know we will require some tonal compression. If it falls on Zone V and we would rather it be on Zone VII, then we know we will need some tonal expansion. This has become automatic for me, as for many of us who grew up with the Zone System.

Nowhere in that process do I characterize subject brightness range as such, though it is built into the process.

It is a matter of craft, at that point, to take the values where they fall, and cause them to be placed where we want them. If we have no real preference (i.e., no visualization) beforehand, then it's a matter of making sure the details that are important to us fall within the capabilities of the film, which gives us the raw materials we need to make those decisions later by whatever means. We might manipulate the placement of values using filtration, dodging and burning, post-processing on the computer, or by manipulating the exposure, speed, and processing of the film. That, as I understand it, is where BTSZ comes in--it adds exposure index as a variable providing an additional degree of freedom in the film-calibration process. (That's about as far as I've gotten with it--what I've been doing until now goes about as far as my technique can support.)

But I pin down the critical point for the film, which is the shadow detail for negatives and the highlight detail for transparencies, and then manipulate the remaining scale, whatever that is for that film, as necessary. That is, to me, the restatement of the traditional truism: expose for the shadows and develop for the highlights.

To me, an incident meter is a model of the scene, while a spot meter takes actual samples. Even if the model is accurate on the whole (in that the light falling on the meter represents the scene being photographed), the difference is whether we want the meter to model how those samples are integrated, or whether we want to perform that integration ourselves. I can see arguments for either approach. But it takes me so little time to sample the scene with a spot meter that I guess I've not been tempted to give that up.

Which leads me back to Ken's original post. I hate meters that provide exposure settings as the output, because then I have to do the math of converting those exposures to where I want the value placed. Give me a straight EV output any day. I realize that modern incident meters don't work that way--I have a Sekonic L-718 that doesn't. I had a Minolta Spot F that was destroyed by accident, but I don't miss it. My Pentax and the Sekonic L-488 meter that I bought to replace the Minolta provide scales that can actually be used with these multi-value systems without a lot of exposure mathematics.

Rick "who uses an incident meter in the studio where the light is all directed at the scene" Denney

Mark Barendt

8-Mar-2012, 07:49

Rick,

First check you instruction sheet (http://www.sekonic.com/images/files/L-718.pdf), your meter can measure and display EV.

Second I don't disagree with you about placement of a specific subject at a specific point.

My suggestion is that a known target placed in the scene, in the appropriate light, eliminates all the guess work.

In the backlit tux scenario I used earlier, regardless of whether we are spot metering the tux, or a gray, black, or white card held against his chest, or using an incident meter held against his chest once the proper offset is applied, the camera readings found should agree. If the spot metering of the tux doesn't agree with the rest, there is probably some human error or extra artistic off set being applied. If there is a disagreement between the various cards and the incident meter, it is human error.

Just as a side note, this known target equivalency with incident metering concept isn't mine, it comes from Dunn and Wakefield's Exposure Manual.

Ken Lee

8-Mar-2012, 07:54

But I pin down the critical point for the film, which is the shadow detail for negatives and the highlight detail for transparencies, and then manipulate the remaining scale, whatever that is for that film, as necessary. That is, to me, the restatement of the traditional truism: expose for the shadows and develop for the highlights.

One refinement included in BTZS - and also described by Minor White (a Zone System proponent) - is that film speed changes with development time. To simply expose for the shadows and develop for the highlights, is to overlook or ignore this fact.

Minor White recommended adding exposure when intending to perform "minus" development, and decreasing exposure when intending to perform "plus" development. His rule of thumb was +/- 1/2 stop for minus/plus 1 development, and +/- 1 stop for minus/plus 2 development.

In BTZS parlance, this amounts to a change in Effective Film Speed at exposure time, based on the measured Subject Brightness Range. With BTZS, a very precise change in EFS is given, depending on the film/developer/paper/reciprocity etc. Whether the photographer can actually work through the entire process with such precision, is another question: adjusting by a fraction of an f/stop may not always be practical or noticeable, but the data is there for the consideration of photographer.

Ken "just trying to follow the facts wherever they lead, and for whom there is always room for improvement" Lee :)

rdenney

8-Mar-2012, 09:23

One refinement included in BTZS - and also described by Minor White (a Zone System proponent) - is that film speed changes with development time. To simply expose for the shadows and develop for the highlights, is to overlook or ignore this fact.

Yes, I mentioned that. They add film speed (exposure index) as a variable to the system, while in Adams's initial exposition, it was held constant (after testing to determine its actual value). Making EI a variable adds one more degree of freedom to the calculation.

Rick "agreeing that 'exposing for the shadow' may present a different target at different target contrast ratios" Denney

rdenney

8-Mar-2012, 09:25

Rick,

First check you instruction sheet (http://www.sekonic.com/images/files/L-718.pdf), your meter can measure and display EV.

Yes, but without that nice mechanical calculation dial, it's not that valuable. Of course, for use with the Zone System, it's not that useful a meter anyway. I do use it with studio flash, where I can control the lighting ratio, and where I can put the incident meter really at the subject location.

Rick "whose subjects are usually too far to place an incident meter in the scene" Denney

Ken Lee

8-Mar-2012, 09:44

Yes, I mentioned that.

Oops - Yes, you did.

Stephen Benskin

8-Mar-2012, 09:50

One refinement included in BTZS - and also described by Minor White (a Zone System proponent) - is that film speed changes with development time. To simply expose for the shadows and develop for the highlights, is to overlook or ignore this fact.

Not as much as you might think. it all depends on how you define film speed. Fixed density point method of the ISO standard is only applicable for that development specification. That is because under those parameters there is a correlation between the fractional gradient speed method and the fixed density speed method. If the development is higher or lower than those parameters the correlation between the two methods is lost. The degree of error progressively increases with increased or decreased development. According to CN Nelson, any speed determination outside the ISO contrast parameters requires another method of determination other than the fixed density method.

That being said, since most people have little awareness of this distinction and still produce quality images this should help to illustrate the tolerances of the photographic process.

rdenney

8-Mar-2012, 09:59

Not as much as you might think. it all depends on how you define film speed.

If we define it as a setting on the meter rather than a characteristic of the film (exposure index versus film speed), we avoid that confusion. And I'm sure that's the point of the process--to provide guidance to the photographer on the settings to use on the meter. It doesn't change the film, it changes the exposure and processing based on what provides a certain outcome with a that film.

Rick "who deals with gozintas versus gozoutas every day" Denney

Ken Lee

8-Mar-2012, 10:29

Not as much as you might think. it all depends on how you define film speed. Fixed density point method of the ISO standard is only applicable for that development specification. That is because under those parameters there is a correlation between the fractional gradient speed method and the fixed density speed method. If the development is higher or lower than those parameters the correlation between the two methods is lost. The degree of error progressively increases with increased or decreased development. According to CN Nelson, any speed determination outside the ISO contrast parameters requires another method of determination other than the fixed density method.

That being said, since most people have little awareness of this distinction and still produce quality images this should help to illustrate the tolerances of the photographic process.

If I understand, you're saying that as development time changes, not only does shadow density change (what we commonly refer to as a change in film speed), but the way we measure film speed must also change ?

It's been a while since I studied differential equations, but that's what this sound like.

Stephen Benskin

8-Mar-2012, 11:22

If we define it as a setting on the meter rather than a characteristic of the film (exposure index versus film speed), we avoid that confusion. And I'm sure that's the point of the process--to provide guidance to the photographer on the settings to use on the meter. It doesn't change the film, it changes the exposure and processing based on what provides a certain outcome with a that film.

Rick "who deals with gozintas versus gozoutas every day" Denney

Rick, if you want to read about it in more detail, you can check out my posts in this thread http://www.apug.org/forums/forum37/99967-what-relationship-between-film-speed-camera-exposure.html "What is the Relationship Between Film Speed and Camera Exposure." I was actually addressing a point about the accuracy of the film speed determination method that Ken brought up.

Ken, it's a question of methodology. The Delta-X Criterion method will produced more accurate film speeds than the fixed density method. And by more accurate, I mean have a greater corrlation with psychophysical testing of photographic prints. The speeds don't change as much with the Delta-X method as it is based on the gradient of the toe which tends to shift in opposite directions to a fixed density. I have the paper on this and will attempt to upload it later.

Stephen Benskin

9-Mar-2012, 06:49

This is what I mean about film speeds. The table below compares film speeds from the fixed density method of speed determination and the Delta-X method using the same set of sensitometrically exposed tests.

69809

jeroldharter

9-Mar-2012, 07:15

Ken,

I am no expert but I use BTZS. I started with a spot meter and ExpoDev for Palm. Then I switched to an incident meter with the Palm. Now i use a simplified version because I prefer Jobo Expert drums for processing but doing one sheet at a time is tedious. Also, I did not like being reliant on a Palm and its battery in the field. The Palm is a pain to use in bright sun BTW.

Now I use a simplified system with an incident meter and a chart. Based on my Plotter graphs/tables,I settled on SBR 5,6,7,8,9 with corresponding film speeds and developing times for each. For 4x5, I have a table which shows me the f stop and shutter speed for each EV for each of the SBR's. I have found that these approximations are close enough so long as I meter correctly. Even with BTZS methods there is still slop in the system from metering errors so my approximations work fine if I meter correctly. Plus, I can use a little Gossen Digisix meter that is nearly weightless along with my laminated chart instead of a larger spot meter, Palm device, car charger, wall charger, spare Palm, etc.

I note my holders to be SBR x and then process them in batches in Jobo drums. Now I do mostly 8x10 so I find it much more efficient than BTZS tubes.

On my laminated table, I also include info on filter factors, filter factors for filter combos (like red plus polarizer), bellows extension, exposure guesstimates for various scenes. So it is a handy cheat sheet that evolves.

One of my annoyances with ExpoDev is that it can't copy the previous exposure to the current exposure. So if I do a series of exposures of the same scene I have to trudge through each window and re-enter data which is no good in changing light.

Mark Barendt

9-Mar-2012, 07:22

Thanks Stephen, that's cool.

Stephen Benskin

9-Mar-2012, 20:47

And therefore 12.5% is what a gray card should reflect, if a reflectance meter is going to recommend the same exposure as an incident meter ?

It's more like 12%, but yes that's basically it. Although you shouldn't get too caught up with reflectances and exposure meters. For starters, reflected meters don’t read reflectance but luminance.

Also, consider different K/C relationships. Keeping the reflected meter’s value of K at 1.16 / 12.5 and changing the incident meter’s value of C to Sekonic’s 31.6 / 340 gives an average reflectance of 11.5. Now, the reflected meter hasn’t changed. How about comparing the same K value with the flat disk value of C = 23.23 / 250? That combination produces an average reflectance of 15.7%. All the while the reflected meter’s calibration hasn’t changed.

Even if you have a reflected meter with a different value of K, it doesn’t really matter because all exposure meters, reflected or incident, want to place the exposure at the same place on the curve and that’s at 8 / Film Speed.

You also have to keep in mind that there isn’t a set relationship between a specific negative density and a specific paper reflection density. It’s about making sure the exposure is placed on the film curve at a place where there is a gradient to separate the scene’s luminance value sufficiently enough to produce acceptable prints.

And it’s not like people haven’t been happily shooting away blissful in the mistaken knowledge that the meter sees 18%. It’s easy to assume that it does because it doesn’t take very much effort to produce results that support that assumption. I’m not just talking about the casual photograph but under testing conditions. The film and paper curve can fit together in a way to shift the mid-tone values upward. Slight variations in printing also can make a difference. As well as the hardest variable of all to control, our selves. How our vision works with such things a simultaneous contrast, general and local adaptation and inhibition, and how it all varies depending on tonal distribution and luminance levels can easily lead to almost any conclusion.

Bill Burk

9-Mar-2012, 22:37

The Delta-X Criterion method will produced more accurate film speeds than the fixed density method. The speeds don't change as much with the Delta-X method as it is based on the gradient of the toe which tends to shift in opposite directions to a fixed density.

Interesting. So a shortcut to using Delta-X might be to take the Exposure Index at CI 0.62 and just don't change EI when you develop less or more.

In other words, I can be lazy but instead of admitting it, I will just tell everyone I'm using Delta-X speeds.

Stephen Benskin

10-Mar-2012, 01:17

Interesting. So a shortcut to using Delta-X might be to take the Exposure Index at CI 0.62 and just don't change EI when you develop less or more.

That's why the higher than normal gradient of the ISO b&w film speed standard doesn't matter. Did you know that the fractional gradient method has no development specification except for a minimum gamma? There is a fairly large processing range where the film speed effectively remains the same. Yes, shadow density will still increase as the processing increases, but as the Delta-X method / fractional gradient method isn't based on density but gradient, this doesn't matter. As this is the case, the just black method of film testing would only be effective with normal processing. I tend to think that most "systems" tend to work in spite of themselves.

The below example illustrates how the a shadow gradient speed point works in relation to a fixed speed point with changes in processing.

69877

sully75

10-Mar-2012, 01:53

Ken,

Just wondering, what's making you go through all of this? Your exposures look pretty spot on to me, and it seems like you have an established system.

Thanks
Paul

Ken Lee

10-Mar-2012, 03:32

Just wondering, what's making you go through all of this?

I have come to this in reverse order: from digital negatives: especially in Platinum/Palladium printing, where trial and error is expensive and time-consuming. Sensitometry can be our best friend.

Although some end-users like to fly by the seat of their pants creatively, the engineers who design film, developers, sensors, lenses, monitors and printers rely on Sensitometry. It is the lingua franca of photography.

The Zone System itself, is really a streamlined form of Sensitometry. While often attributed to Ansel, it was likely created by a scientist at a film manufacturer who was an expert in... Sensitometry.

Your exposures look pretty spot on to me, and it seems like you have an established system.

There's always room for improvement. Photoshop can rescue and improve things here and there, but having grown up with darkroom printing - a completely analog process - I see that fewer corrections lead to better images, and up-stream corrections are best. BTZS is all about that, just as the Zone System is.

For many of us, tonality and fidelity are among the principal reasons for choosing film and Large Format equipment. If BTZS can improve things a few percent: either better images or fewer failures, then it will be worthwhile.

If it means starting over, that's OK. It's good to stay a beginner. As one Zen master put it: "In the beginner's mind, there are many possibilities. In the expert's mind, there are few".

If it's a dead end, I'll go back to what I've been doing :)

sully75

10-Mar-2012, 04:16

Got it. Have you found BTZS to be the most interesting to you? I've been thinking about digging in to that a little deeper myself.

Ken Lee

10-Mar-2012, 05:56

Have you found BTZS to be the most interesting to you?

It's interesting, that's for sure. One thing I've discovered in trying to grasp it, is that every system is a compromise of one kind or another. Just start reading Stephen Benskin's posts here and on APUG, and you'll soon realize that.

It shouldn't be surprising, because in the end, we're dealing with analog processes. Things in Nature are curved and wiggly, no matter how much we try to bang them straight and nail them down. So even BTZS, with its additional complexity, is still just another "streamlined version" of Sensitometry.

I've been thinking about digging in to that a little deeper myself.

Although some people prefer to "wing it" creatively and do everything by feel, even something as apparently simple as B&W photography contains many parts: tone, texture, composition, lighting, perspective, etc. Sensitometry (which some prefer to call "technique" or "workflow") is just another one of those parts. They're all important, and we're all "called" to concentrate on different ones at different times. So if you're drawn to it, dig a bit and see what comes up. You'll find out if it's a dead end, soon enough. I haven't investigated this stuff since 1970, but now's the time. It's calling me.

When I worked on fences, all I could see when out driving, was other people's fences - but that passed eventually. Now that I'm studying BTZS, all I can see is Subject Brightness Ranges and step wedges. I'm confident this phase will pass, and that it will be a growth phase.

Stephen Benskin

11-Mar-2012, 11:03

Here is a nice little paper from a lecture by Jack Dunn in 1962 about incident meters titled Expose for the Middle Tones. It copied by OCR so I hope I caught all the errors.

The second attachment is an excerpt which deals with the Delta-X Criterion from Nelson's Safety Factors in Camera Exposure. The Delta-X paper I wanted to upload is too large. Safety Factors is the paper that lead to the fixed density method in the 1960 ASA standard and all subsequent versions.

Bill Burk

11-Mar-2012, 12:17

69983

So the close correlation here means that if you track 0.1 density, and cross-reference Delta-D and lookup Delta-X.

You use Delta-X to find the 0.3 G which is difficult to find by other means.

And it has always been known that 0.3 G is the speed at which "first excellent" print emerges.

Right?

Stephen Benskin

11-Mar-2012, 12:26

So the close correlation here means that if you track 0.1 density, and cross-reference Delta-D and lookup Delta-X.

You use Delta-X to find the 0.3 G which is difficult to find by other means.

And it has always been known that 0.3 G is the speed at which "first excellent" print emerges.

Right?

Right, but to avoid confusion, maybe it should be referred to as speed method as the speed constant can be changed independently of the methodology.

Ken Lee

11-Mar-2012, 14:10

Here is a nice little paper from a lecture by Jack Dunn in 1962 about incident meters titled Expose for the Middle Tones.

Thirdly, long-range subjects (progressively longer as the lighting angle increases) are reproduced to "spill over" equally beyond the film acceptance range at both ends: i.e., the middle normal-range "slice" of the longer overall scene range occupies the full film reproduction range, and the extreme highlights and the extreme shadows both overspill progressively more and more (but still more-or-less equally at both ends of the scale) as the lighting angle increases.

I love how well he writes, but unless I'm mistaken, he's suggesting that in cases of high subject brightness range, we simply meter for the middle, and let the chips fall where they may, or in his words "spill over equally beyond the film acceptance range at both ends"

Isn't that what we're trying to... avoid ? Both the Zone System and BTZS endeavor to avoid that very scenario (and more of course).

Have I overlooked something ?

Mark Barendt

11-Mar-2012, 14:22

I think you have it Ken.

Stephen Benskin

11-Mar-2012, 14:26

Ken, I believe he is referring to reversal material.

Ken Lee

11-Mar-2012, 15:12

Stephen Benskin

11-Mar-2012, 15:45

While he mentions that tests were performed with color slide films, but he also states the following:

"The writer nowadays almost invariably uses this method for negative materials (monochrome and colour) as well, and would not revert to any other except in special cases which call for the use of an exposure photometer"

May be I've misunderstood what he means.

This was a personal statement of the authors and was presented as an aside. I have to assume Dunn knows the shadow detail requirements of negative materials and he doesn't go into sufficient detail about the "special cases" for us to come to any conclusions. All the testing information presented in the paper as well as Figure 1 all have to do with reversal films. Don't forget where he said that the incident meter is "slightly limited in application." It's been awhile since I've carefully read Dunn's Exposure Manual, but I do know he discusses this in more detail. He has even reproduced Figure 1 for the book.

Remember to keep in mind that nothing is perfect. We need to identify the strengths and weakness and learn how to make them work to our advantage.

Bill Burk

11-Mar-2012, 16:47

Right, but to avoid confusion, maybe it should be referred to as speed method as the speed constant can be changed independently of the methodology.

Well then, count me in. I'll find a way to make Delta-X work for me.

I always thought sliding EI with development was difficult to implement in the field.

Now my big question: I wonder if there are two different possibly "stories" that go with altered processing.

There is the processing that varies because it is "out of control."
-The amateur who has difficulty controlling temperature and time, would "really" get higher speed for longer development and lower speed for less development. Assuming the subject in the amateur's case had average (or not evaluated) subject brightness range.

And there is the processing that is varied appropriately in response to subjects with ranges of shorter and longer scale.
-This is where Delta-X would be a more valid speed method.

Do you think these scenarios would apply?

david.jade

11-Mar-2012, 16:58

One of my annoyances with ExpoDev is that it can't copy the previous exposure to the current exposure. So if I do a series of exposures of the same scene I have to trudge through each window and re-enter data which is no good in changing light.

fyi, this feature will be coming to the new version of ExpoDev.

Mark Barendt

11-Mar-2012, 17:35

Stephen Benskin

11-Mar-2012, 17:43

Well then, count me in. I'll find a way to make Delta-X work for me.

I always thought sliding EI with development was difficult to implement in the field.

Now my big question: I wonder if there are two different possibly "stories" that go with altered processing.

There is the processing that varies because it is "out of control."
-The amateur who has difficulty controlling temperature and time, would "really" get higher speed for longer development and lower speed for less development. Assuming the subject in the amateur's case had average (or not evaluated) subject brightness range.

And there is the processing that is varied appropriately in response to subjects with ranges of shorter and longer scale.
-This is where Delta-X would be a more valid speed method.

Do you think these scenarios would apply?

Actually, one of the arguments for adopting a fixed density method with the contrast parameters was that the photo labs had gained a greater control over their processing. Because the fractional gradient method basically has only one speed at most levels of processing, it is very tolerant of sloppy controls. As such, Delta-X should work equally well with both scenarios. It's not really necessary to use Delta-X, but I believe understanding the concept increases our knowledge of what film speed really is.

I've been wondering lately how Phil Davis would feel knowing that he is at fault for generations of photographers using the wrong term "brightness" instead of luminance. No, it's not the same as saying "ASA" instead of "ISO". Brightness and luminance have two different meanings. Davis does make a small mea culpa in BTZS, but I guess the contrition wasn't sincere enough to actually make corrections to the book.

sanking

11-Mar-2012, 18:16

I've been wondering lately how Phil Davis would feel knowing that he is at fault for generations of photographers using the wrong term "brightness" instead of luminance. No, it's not the same as saying "ASA" instead of "ISO". Brightness and luminance have two different meanings. Davis does make a small mea culpa in BTZS, but I guess the contrition wasn't sincere enough to actually make corrections to the book.

If what you say is true, i.e. "generations of photographers using the wrong term "brightness" instead of luminance" it would not be the fault of Phil Davis, but of people who have never read his book or attended one of his workshops. Davis made it very clear in his workshops and in his books that what he calls SBR is in fact subject luminance range.

"Despite the fact that subject brightness range is incorrect it is generally understood, and its abbreviation, SBR, is distinctive and useful. (SLR can't be used because it means single-lens reflex to most photographers.). You'll see both terms in this book, but remember that SBR means subject luminance range." Beyond the Zone System, 3rd edition, p. 28.

So to be clear, the use of the the terms SBR was not an error, but quite deliberate on his part, and not something for which he would seek contrition.

Sandy King

Stephen Benskin

11-Mar-2012, 19:00

It's just a pet peeve of mine. My experience is that the explanations are frequently forgotten. Take for example, the reasons for the contrast parameters in the ISO speed standard. They are almost completely forgotten and almost universally misinterpreted.

According to the Encyclopedia of Photography 3rd ed., "The visual experience that is approximately correlated with the luminance of objects seen as light sources. Since brightness is a psychological concept, there are no units of measurement as there are for luminance, a psychophysical concept." According to The Theory of the Photographic Process, 3rd ed, "Brightness is the magnitude of the subjective sensation produced by light and luminance is the magnitude of the stimulus (light). The relation between brightness and luminance is complex and is dependent on the state of the eye with respect to adaptation and inhibition. Luminance can be measured accurately with a photometer but brightness can be determined only approximately, by means of psychological scaling procedures."

In fact, the two are so separate that they can be graphed against each other. A luminance vs brightness graph of the response of human vision, will make anyone question the whole concept of the placement of values.

LSLR is frequently used for log subject luminance range.

Mark Barendt

12-Mar-2012, 04:53

While he mentions that tests were performed with color slide films, he also states the following:

"The writer nowadays almost invariably uses this method for negative materials (monochrome and colour) as well, and would not revert to any other except in special cases which call for the use of an exposure photometer"

Maybe I've misunderstood what he means.

The special cases Dunn refers to, as I remember, are 1-shorter range scenes on B&W and 2-when purposefully minimizing exposure on B&W. Dunn and Wakefield actually advocate for use of those techniques and for adjusting metering techniques there.

For longer range scenes, any shot with a face, and all forms of color work (negative or positive) pegging the middle is recommended by Dunn and Wakefield.

Stephen Benskin

13-Mar-2012, 11:19

In the Long Range and Controlled Lighting Still Monochrome Photography section of Exposure Manual, I believe Dunn is expressing a personal choice about how to handle the longer luminance ranges. It appears he feels the compression of tones from reduced processing for the longer luminance range is more detrimental then having to work with a negative with a higher than normal density range.

"In general, therefore, it is often bette in such cases to develop the negative normally and to print on to a normal paper, and then to adopt one of the following two procedures - namely (a) if reproduction of shadow and highlight detail is essential, to overpritn the highlights in the enlarger by using a shading or masking technique of (b) if - as is usually the case - the main interest is only at one end of the scale, to print for that end only and ignore the other end entirely. In the writer's opinion - and he believes this to the generally accepted view - it is in such cases almost invariable the highlights and middle tones that are required at the expense of the shadows, especially when the latter are small."

Mark Barendt

14-Mar-2012, 04:47

As I remember his thought was basically that negatives done with minus development provided local contrast rates that were generally too flat in print.

The other thing is that the opinion he's providing is based a a lot of study about what most viewers actually prefer. He leaves ample room for special cases.

My take on that idea is that; sure we can get a 12-stop scene to straight print on a particular grade of paper but, that's just a technical exercise if it lacks the snap to catch the viewers eye. If we have to print harder to make it look right the minus development didn't help us any.

Stephen Benskin

14-Mar-2012, 05:24

Mark, I'm not saying Dunn is wrong. He is expressing an opinion on a possible approach. Although he doesn't define the parameters, I doubt he uses much beyond one or two stops over the average luminance range. And while he doesn't go into detail about how deep the shadows have to be or how small they need to be to sacrifice them without a detrimental impact to image quality, there are accent blacks that aren't considered part of the average luminance range which is what he might be referring to. I personally opt to use a printing approach for slightly longer than average luminance ranges rather than a change in processing depending on the subject, for example, to control the sky. My point is that there are no hard and fast rules, especially when it comes to technique.

Mark Barendt

14-Mar-2012, 16:34

The point I'm trying to get to here applys directly to BTZS and incident metering in general.

It's so obvious it's hiding in plain sight. ;)

We're talking about measuring the light, not reflectance.

What I'm getting at here is that, as far as i can tell, with normal incident readings and in the BTZS, specific tones are never measured. We can't say that "that shadow under that tree is going to be placed at zone 2 or 3", because it's never measured regardless of its size in relation to the rest of the scene.

The exact point in a specific real life scene where tones start to fall outside the film's acceptance range simply isn't identified by incident data.

When we peg the midtones we have to "trust" that our vision/judgement/experience/skill/testing/system works, we aren't picking specific cut off points from the scene. We are placing/pegging mid tones and allowing the rest to fall where it may.

Dunn's duplexed incident metering and the BTZS both allow shadows to fall where they may. Granted they provide very, very, very good guesses about placement.

To place specific tones, Dunn's special cases, we need to switch to spot metering, for example, that shadow under the tree, and placing it exactly where we want it in relation to the toe of the film curve.

Stephen Benskin

14-Mar-2012, 17:46

To place specific tones, Dunn's special cases, we need to switch to spot metering, for example, that shadow under the tree, and placing it exactly where we want it in relation to the toe of the film curve.

Or relatively where we want it. Flare.

Mark, I believe we're in agreement here. I was telling Ken the other day that systems try to simplify things in order to shoehorn everything into a set of rules. Most things are more complex and nuanced than that.

Mark Barendt

14-Mar-2012, 20:48

Or relatively where we want it. Flare.

Mark, I believe we're in agreement here. I was telling Ken the other day that systems try to simplify things in order to shoehorn everything into a set of rules. Most things are more complex and nuanced than that.

Yes, I believe we agree.

Bill Burk

15-Mar-2012, 07:14

My take on it is that Dunn's midpoint metering is classic what you get if you do nothing. A hard to print negative that requires burning in highlights.

BTZS at least makes straight printing possible because you analyze range and develop accordingly. You place exposure according to a simulated shadow reading (which places shadows in a low Zone).

But Zone System metering is unique. You spot important subject and place on the Zone (relatively where you want because of flare). You analyze range and determine plus or minus developing... Zone System has the flexibility to give you midtone metering, shadow placement or previsualized metering to achieve stylized results.

The possibility for stylized results attracts me to Zone System. And how Minor White used it.

Mark Barendt

15-Mar-2012, 11:23

Bill,

It's a matter of balancing competing priorities and applying our experience.

Incident metering, in normal use, can place exposure in such a way that with a standardized printing setup we get a very close to finished placement of say a face on the paper. This is exactly like placing exposure for trannies. It provides a very workable straight print, with subjects very close to finished, but not one that will show the whole Range of the background available to print.

That is something the Zone System and spot metering don't normally do. Instead they typically place the shadow and allow the face to fall where it may. We are left with a print that may be right at the ends but screwy in the middle.

Both systems work, and can provide equal quality, they just have require different work to finish.

rdenney

15-Mar-2012, 17:01

This is something the Zone System and spot metering don't normally do. Instead they typically place the shadow and allow the face to fall where it may.

It seems to you are blaming the system for how might be misapplied. There is nothing about the Zone System that prevents me from placing the face on whatever zone I choose, and then seeing where other values fall. The face may still be the key to the exposure, if I choose it to be. The Zone System is about deciding what we want those values to be, and then manipulating craft to achieve that.

Incident metering is a model of lighting only, because what exposes the film is not the lighting , but rather the portion of the lighting that is reflected back to the camera. That model is only accurate under certain circumstances, it seems to me. When I can control the lighting, and measure that lighting at the subject that I want in the middle of the range, then I use incident metering.

Luminance metering is not a model. It is data. What we do with it is up to us.

Rick "systems don't make decisions, photographers do" Denney

Mark Barendt

15-Mar-2012, 17:51

It seems to you are blaming the system for how might be misapplied. There is nothing about the Zone System that prevents me from placing the face on whatever zone I choose, and then seeing where other values fall. The face may still be the key to the exposure, if I choose it to be. The Zone System is about deciding what we want those values to be, and then manipulating craft to achieve that.

Incident metering is a model of lighting only, because what exposes the film is not the lighting , but rather the portion of the lighting that is reflected back to the camera. That model is only accurate under certain circumstances, it seems to me. When I can control the lighting, and measure that lighting at the subject that I want in the middle of the range, then I use incident metering.

Luminance metering is not a model. It is data. What we do with it is up to us.

Rick "systems don't make decisions, photographers do" Denney

Rick I'm not blaming the system. My descriptions above are simply examples of the normal classic uses.

Also Dunn and Wakefield make the point in the Exposure Manual that spot metering a known target, like a face (skin tone) we know, is essentially incident metering.

rdenney

15-Mar-2012, 21:58

Rick I'm not blaming the system. My descriptions above are simply examples of the normal classic uses.

Also Dunn and Wakefield make the point in the Exposure Manual that spot metering a known target, like a face (skin tone) we know, is essentially incident metering.

Well, it's not how I use the Zone System, or how Adams wrote about it. I'll leave it at that.

An incident meter assumes that the light falling on it integrates to middle gray (and I'll let others argue about what that means). Supposing I want to render a tanned face in high key? Supposing I want to light up the face of a person of color? Supposing faces aren't my subjects? When I see the word "essentially", I don't see disagreement with my characterization of it as a model.

Rick "who uses the Zone System even with slide film" Denney

Bill Burk

15-Mar-2012, 22:24

Mark, I agree most users learn Zone System and carry it no further than spot shadows and judge development for straight documentation, literal representation.

As Rick stated, the High-Key, Low-Key, stylized interpretations are where Zone System has less-commonly-realized potential.

While incident metering (and expanded range incident metering a-la BTZS) can give you the accurately placed exposures, incident metering doesn't give you the tools to plunge a puddle into black Zone 0 for an abstract. (Maybe it does but that's the point I think Rick is making).

I find myself more comfortable in the field with a combination Spot/Incident meter than with a combination Incident/Averaging meter.

That's because I believe both Spot and Incident have their place. I'm not so sure about averaging.

Ken Lee

16-Mar-2012, 04:29

http://www.kenleegallery.com/images/forum/VennDiagram.png

I'm no expert, but everything I've read about BTZS suggests that it is a superset of ZS methodology, not a replacement for it. Were this not the case, I would probably not have taken it up for study. In the above Venn diagram, B is a superset of A. In other words, A is a subset of B.

Phil Davis' book describes the Zone System not in passing, but as a core component. The third edition contains several photos that are described as having been made with the Zone System, and numerous diagrams which show the correlation between BTZS and Zone System terminology. He points out the strengths and weaknesses of both systems.

The ExpoDev and Plotter programs work with SBR and Zones interchangeably: both are fully supported.

Had Phil developed his system in today's computer-centric world, he might have called it "ZoneSystem++", or "Zone System 2.0".

Mark Barendt

16-Mar-2012, 04:49

Rick I'm not trying to advocate for one system or the other here, just for understanding what they do.

Yes, the incident meter assumes that "the light it's in" integrates or averages out to middle gray, but like you also said "systems don't make decisions, photographers do". Regardless of the metering method we use, we have to ask ourselves "what am I measuring" and factor that in to find what we might consider a normal camera setting. From there we have to decide if we want it to render normal or high or low.

BTZS users factor in what they are measuring when a shaded reading is taken as the basis for setting the camera exposure. That concept is also used when they find the difference between their shadow and highlight measurements to help them decide on their EI and processing.

Dunn uses that concept when Duplexing, which he did with a flat face incident meter.

With regard to different skin tones and spot metering those faces, as long as the placement offset to a "normal" camera setting is "a known" it doesn't matter what the specific tone is, this is a true zone system concept and equal in practice to incident metering. With an incident meter we don't need "a known" target (skin tone or whatever else) in the scene to find the same camera setting.

Mark Barendt

16-Mar-2012, 05:01

incident metering doesn't give you the tools to plunge a puddle into black Zone 0 for an abstract. (Maybe it does but that's the point I think Rick is making).

I agree, spot metering can tie a specific tone to a specific point on the film curve, incident metering can only infer that relationship, but with a little experience it can infer that very well.

Bill Burk

16-Mar-2012, 07:27

With regard to different skin tones and spot metering those faces, as long as the placement offset to a "normal" camera setting is "a known" it doesn't matter what the specific tone is, this is a true zone system concept and equal in practice to incident metering. With an incident meter we don't need "a known" target (skin tone or whatever else) in the scene to find the same camera setting.

And in this sense, reading off your palm and opening one stop is the ultimate incident meter.

And also, Minor White invented BTZS. His "Zone System Manual, How to Previsualize Your Pictures" outlines "Short Cut Exposure-Development Calculations"

1. Take a meter reading off the palm in shadow
2. Place on Zone IV to set exposure
3. Take a meter reading off palm in sun
4. Development determined by difference in the two readings.
5-Zone difference N-2
4-Zone difference N-1
3-Zone difference N
2-Zone difference N+1

rdenney

16-Mar-2012, 09:14

I know little about BTZS, but my issue is with the justification for using an incident meter. It seems that the justification is to be easier, but using it shaded, aimed at the light source, then with a flat diffuser, and so on, is at least as fiddly as using a spot meter to measure several parts of the scene.

Given that an incident meter is not measuring directly what the film sees, I can't see how it could be more accurate, though even Sunny 16 works in the hands of a skilled user, so I'm sure it could be as accurate. To be as accurate, though, it seems to me we have to apply subject-specific effects that would be explicitly measured using a spot meter.

I have no complaint with whatever BTZS might do to recognize that development for different contrast affects zone placement, in terms of density, etc. That seems a separate issue, and for that discussion, I listen only.

Rick "who, by the way, owns a very nice incident meter for controlled lighting" Denney

Bill Burk

16-Mar-2012, 09:17

...everything I've read about BTZS suggests that it is a superset of ZS methodology, not a replacement for it. ...Phil Davis' book describes the Zone System not in passing, but as a core component. The third edition contains several photos that are described as having been made with the Zone System, and numerous diagrams which show the correlation between BTZS and Zone System terminology. He points out the strengths and weaknesses of both systems..

Then I oversimplify when I categorize BTZS as an incident metering only system.

I am still fascinated by Minor White's "Short Cut Exposure-Development Calculations" - as it sets the stage for what Phil Davis codified in BTZS.

Bill Burk

16-Mar-2012, 09:31

...about BTSZ, but my issue is with the justification for using an incident meter. ...

My issue with it too, however as Ken points out, the actual BTZS reference book and software contains and supports Zone System technique.

Ken Lee

16-Mar-2012, 11:53

According to Wikipedia (http://en.wikipedia.org/wiki/Subset):

In mathematics, especially in set theory, a set A is a subset of a set B, or equivalently B is a superset of A, if A is "contained" inside B. A and B may coincide. The relationship of one set being a subset of another is called inclusion or sometimes containment.
BTZS includes the Zone System, not the other way around. The same may be said of Sensitometry in general: it contains BTZS, but not the other way around.

Bill Burk

16-Mar-2012, 13:40

BTZS includes the Zone System.

I think we're saying the same thing.

I admit I'm wrong to take issue with "BTZS" when I only take issue with "BTZS - Incident Metering". I'll try to be more clear when I say things like "When I read BTZS - Incident Metering, I couldn't figure out how to create stylized renditions so I decided to stick with Spotmetering."

jcoldslabs

16-Mar-2012, 13:55

Does embarking on this detailed of a procedure at the outset to determine proper exposure only pay off if your shutter speeds and aperture settings are accurate to within 1/3 stop and if you develop for precisely the prescribed amount of time at precisely the level of agitation with precisely the same dilution of developer every time? Any process is only as accurate as the sloppiest link in the chain, and it would be a shame to lose some of the attempted metering precision because of a faulty darkroom thermometer. Or are there equally rigorous processing procedures proscribed by BTZS?

As much as I appreciate those who can wrap their minds around the BTZS methods (I cannot), I know the other steps in my processing will never be as accurate and therefore I don't worry about it. None of my old shutters is CLA'd or calibrated, for instance, so exposing with pinpoint accuracy will never be possible no matter how well I meter a scene. Sort of like having pristine vinyl records, a $3,000 turntable, a $5,000 amplifier and $100 speakers. But my hat's off to those of you with the smarts and the motivation to both understand and practice the methods outlined in this thread. I feel a bit like I do when I read about quantum mechanics: it is fascinating, but my small brain does not have the power to fully grasp it.

Jonathan

Bill Burk

16-Mar-2012, 15:46

Does embarking on this detailed of a procedure at the outset to determine proper exposure only pay off ...

For me it's like a game of darts. Just hitting the board is a good thing. If you keep hitting low it helps to aim up a bit.

jcoldslabs

16-Mar-2012, 17:24

Bill,

I figure consistency is as good a plan as any. I use the same old shutters all the time, so the slow speeds are built into my process, the same old uncalibrated meters, the same developer and dilution, and I develop with some temperature and agitation sloppiness built in so my results are targeted with a range, not to the furthest decimal place. Bullseyes are great, but like you I am content with hitting the board and adjusting my aim as I go.

But to be clear: I have great admiration for those who refine their processes and routinely test until they achieve the results they want. I have seen prints from nearly perfect negatives (a subjective term, I know) that blow me away. I know my work will never get there, but I have made peace with that fact.

Jonathan

Shen45

16-Mar-2012, 17:42

There is an expression about a committee designing a horse and ending up with a camel and so it seems from most people that have only read the BTZS book but never used the "system". BTZS is not the Zone system. It is similar but oh so superior in many ways. I find it refreshing that Ken is actually setting out with the intention of using the system as designed. I've used BTZS for about 7 years now and initially just reading the book was "challenging" to say the least, however when I put aside preconceived ideas and practices from my past things started to make sense. I forked out for all the software, a densitometer and the processing tubes. I had to learn the methodology, the terms and accept what I felt may have been short comings of the system as a whole. The short comings were more mine though due to trying to use the system in ways contrary to its designers intent.

If you choose to go BTZS with the lot then you will need to set up your darkroom with the ability to test your film according to the requirements of the system. No other test data or method will work - for BTZS. It is an integrated system.

The Plotter program requires a known standard and that [for me] was/is based on Delta 100 processed in D76. Phil Davis lists both Delta and Tmax 100 as reaching a genuine 100 iso.

The requirements for calibrating your own enlarger for your personal speed point may take an afternoon but is only done once. This calibration step accounts for your enlarger, timer, thermometer and agitation. You expose film in contact with a step wedge and read that into the plotter program. For the PSP test 3 sheets are exposed using an accurate repeatable digital [preferably] timer and then processed for 4, 8 and 16 minutes. The step wedges are then analysed by the plotter program to determine what your PSP is. If the PSP value you get from your set up matches the figure Phil has determined your testing standard has been established. If not the BTZS site has simple instructions to get it all set correctly. Once determined you will have an EV reading of your enlarger light source and a PSP number for the plotter program.

Once you have your PSP determined ---

The premise of BTZS is tying everything back to the media you are going to print on. About 2 hours testing of your paper will determine the actual grades of the paper and an "ES" value that will be used by the plotter program when you create an exported file for the Palm or the new iOS version of ExpoDev. Your paper testing must be done using the actual enlarger or light source you use for printing.

To test your actual film, set the EV of your enlarger to the one you determined with your initial test adjusted up or dawn to account now for the boxed speed of the film you are testing. EG if the 100 iso standard requires EV4 then a 200 iso box speed film will require the enlarger to be adjusted to EV3 for the series of step wedges.

Five sheets are exposed identically and then processed at 4, 5:40, 8, 11 and 16 minutes. You can if you wish increase the 16 minute time to 20 minutes if your developer is capable of sustained development to that time and that can sometimes give you a greater range from the film you are testing. D76 is one developer that can easily develop to that time without the resultant film curve becoming misshaped due to developer exhaustion. The results are read into the plotter and your testing is basically completed. The plotter analyses the wedges and sets the point of darkest texture and based on your tested ES value the brightest highlight with just visible texture. The plotter sets other important points of course including the speed that your film has tested at. From a very small amount of effort you now have a collection of data including the SBR [range] of your film. Times temperatures and film speeds. Zones and more. A file can now be exported to your mobile device with the ES applied for your paper grade you want to print on.

BTZS testing will very quickly show you what a film/developer combination can and cannot handle. BTZS testing will only give you useful data within what the film/developer combination can be expected to produce high quality easily printable negatives. If your light conditions in the field exceed your test results ExpoDev will tell you you have exceeded the capabilities of the film.

BTZS allows you to use either Incident or spot metering, I use both, and both work equally as well. Both can be used for "creative" placement of tones within the range of your tested film. Both have their own particular limitations in any type of photography but these are minor and once metering experience is gained with the system both work equally as well.

There appears to be a basic lack of understanding of what BTZS really is on this and other fora, BTZS is not the Zone system. It is similar but oh so superior in many ways. it is a complete system of testing exposure [factors, bellows, reciprocity and individual sheet development times]. The learning curve initially is a bit steep but it is soon forgotten and becomes an automatic part of your photographic arsenal. BTZS has bucket loads of info for the photo geek but if figures bore you then those figures will not even concern you as you take your first beautifully exposed and developed negative to your enlarger. Phil Davis was certainly a photo geek but he was also extremely practical and his wonderful system reflects that.

Steve

Ken Lee

16-Mar-2012, 20:10

"If you choose to go BTZS with the lot then you will need to set up your darkroom with the ability to test your film according to the requirements of the system. No other test data or method will work - for BTZS. It is an integrated system..."

Thank you Steve - the timing of your message is fortuitous !

I just dusted off my enlarger, and put in one of my shutter-mounted view camera lenses. I'm hoping to do my first film test. (I had Fred Newman do one for me, so I know what to follow). I have a step-wedge and my densitometer will be back from the shop in a few days.

My wife tells me never to sell my old equipment, and I have to admit that I was thinking of ditching my enlarger - but now I'm really glad I kept it.

Even though I'm fairly familiar with the Zone System and manage to get some decent exposures now and then, it has been a valuable experience to study BTZS. More than simply giving a deeper understanding of how things work, it's having an impact on how I see.

For years I have seen things in terms of tones - perhaps a result of measuring reflected light. Using an incident meter places greater emphasis on the interplay between direct and indirect lighting - and makes one more aware of the quality of the light itself.

Stephen Benskin

16-Mar-2012, 20:36

Ken Lee

17-Mar-2012, 04:18

Shen45

17-Mar-2012, 05:45

Steve, this is something that I've been wondering about for sometime. What was Davis' reasoning for choosing to do a "work around" by increasing the aim negative density range when incorporating flare into curve analysis (page 95 3rd ed)? From my experience people tend to forget the reasons for a work around leading to misconceptions on how the underlying principle works. Also, what percentage of BTZS users do you think actually incorporate this flare adjustment into their analysis?

Hi Stephen,

Thanks again for your knowledgeable contribution to this forum. I cannot speak to why Phil did what he did with BTZS but can attest to the most predictable and printable negative I have even had. I used the ZS for many years and while it works well the consistency of the negatives with BTZS is the real winner for me. As to flare the plotter doesn't "add" flare to the file created for export to the ExpoDev, that is something you add as a personal preference. For example for my Verito I use a different value compared to my RD Artar. Essentially the flare factor is more an experience thing. I also apply a different factor for one of my older cameras relative to a much newer camera with newer bellows. I would say most BTZS user based on the Expodev program apply a flare factor between .015 and .03.

Steve

Shen45

17-Mar-2012, 05:55

If a scene is back-lit, how can it be evaluated with an incident meter ?

For example: a person standing directly in front of a window, in a white room. Most of the light is coming into the room through the window behind the person, and there is a little "fill" effect from the room.

We don't want the window behind the person to be pure white, and we'd like to know where it will be, depending on exposure, so that we can control contrast. The scene may be too contrasty for ordinary methods, but how do we evaluate it ? How do we determine the Subject Brightness Range ?

In a sense, the entire scene is in shadow, so getting a shadow reading is easy. Placing the meter in front of the person's face and pointing it towards the camera, we can measure the shadow illumination - but how do we meter the window itself ? If we hold the meter up against the window and point it towards the camera, the meter dome is shielded by the back of the meter, and all we get is another shadow reading.

Hi Ken,

Highlight = Dome facing away from camera pointing at the brightest part of the window. Examine the window to see what is the brightest part of the scene and get as close as you can so the meter is evaluating just the highlight. That is your highlight reading.

Shadow = Dome at subject position pointed to the camera.

ExpoDev does the rest. If you want the window to "blow out" a little just point the meter toward the next less bright area of the window highlight area and use that lower highlight EV. Another way is to meter the brightest area you can find and add or subtract .5 to 1 EV. Incident metering does offer excellent creative possibilities.

Hope that helps.

Steve

Stephen Benskin

17-Mar-2012, 06:55

I cannot speak to why Phil did what he did with BTZS but can attest to the most predictable and printable negative I have even had. I used the ZS for many years and while it works well the consistency of the negatives with BTZS is the real winner for me. As to flare the plotter doesn't "add" flare to the file created for export to the ExpoDev, that is something you add as a personal preference. For example for my Verito I use a different value compared to my RD Artar. Essentially the flare factor is more an experience thing. I also apply a different factor for one of my older cameras relative to a much newer camera with newer bellows.

There's no doubt about the negatives. BTZS uses good solid tone reproduction theory. My major concern with BTZS is that Davis tends to gloss over some concepts. Maybe it's the simplification inherent to "systems" or maybe it's just to keep the book to a reasonable length. Otherwise, I agree with most of what he says.

I would say most BTZS user based on the Expodev program apply a flare factor between .015 and .03.

Isn't this the adjustment with the program? I'm more interested in how Davis describes factoring in a flare adjustment on paper and whether this concept is one that people tend to follow. While we're on the topic of the program, exactly how does it calculate the flare factor? Can you explain the math here?

Mark Barendt

17-Mar-2012, 06:55

The difference between the reading pointed at the light source, the window in your example, and the reading pointed at the camera tells us if the scene is a short, normal, or long scale. You use that info to decide on EI and processing.

Then those readings are used to decide on placement.

My impression is that BTZS pegs placement from the "at the camera" reading, Dunn averages the two readings to place exposure.

If a scene is back-lit, how can it be evaluated with an incident meter ?

Bill Burk

17-Mar-2012, 08:50

For years I have seen things in terms of tones - perhaps a result of measuring reflected light. Using an incident meter places greater emphasis on the interplay between direct and indirect lighting - and makes one more aware of the quality of the light itself.

Ken,

This post brought tears to my eyes, these few words have changed my attitude towards incident metering.

Ken Lee

17-Mar-2012, 10:52

Highlight = Dome facing away from camera pointing at the brightest part of the window. Examine the window to see what is the brightest part of the scene and get as close as you can so the meter is evaluating just the highlight. That is your highlight reading.

Shadow = Dome at subject position pointed to the camera.

http://www.kenleegallery.com/images/forum/Sink.png
Rangefinder Test, 2012
Mamiya 7, 150mm Mamiya N
TMY, Pyrocat HDC

I just gave your recommendation a try, and I have to admit that it worked much better than I had anticipated. This photo was made to test the accuracy of the rangefinder at medium distance. I got the high reading from the window itself, but I exposed for the shadow reading, as recommended in the BTZS book.

To me, this illustrates one of the advantages of incident metering: not having to pre-visualize. Almost everything in the subject is white, and there was nowhere obvious for me to place any of the zones. With this approach, the zones (many of which don't fall on a roman numeral if you know what I mean) took care of themselves.

Mark Barendt

17-Mar-2012, 12:28

david.jade

17-Mar-2012, 15:09

While we're on the topic of the program, exactly how does it calculate the flare factor? Can you explain the math here?

I can answer this one for both Plotter and ExpoDev:

Flare in ExpoDev is rather simple. The Film Profiles that are exported from Plotter contain no flare information at all (it always gets stripped since Flare in Plotter is just a simulation). Flare as set in ExpoDev is used to to modify Average Gradient that is calculated (which is derived from the SBR and the Paper ES). It is simple a factor which gives a little boost to the calculated Average G. Average G is then used to look up the EFS value from the imported film curve so effectively, Flare typically (but not always depending on the curve) gives a slight boost to the EFS that will then be used to set the exposure. It is a pretty simple compensation factor.

Flare in Plotter is used to simulate the effects of Flare when analyzing film curves. The math behind it there is quite a bit more complicated. Flare is a density value and Plotter tries to find the exposure value that would produce that density from the data points in a film curve. Once it finds the exposure value that produces that density, it then uses that as a exposure component to adjust all the points in the curve to get the flare adjusted density values.

So if FE is the exposure value that produces a Flare density of FD and for each point on a curve an exposure value of IE produces a density of ID, then the flare adjusted density for each point in a curve becomes the ID density for an exposure value of FE + IE. Because we're working with log exposure values, the effects of any arithmetically added flare exposure is variable over the curve.

The effect this has is, as the exposure value for each point on the curve increases the effects of flare become less and less. This is because exposure values increase in stops but flare is a minor exposure component arithmetically added to each point. In other words, flare's effect in increasing density are more pronounced in the toe of the curve than further up the curve. In fact up near the shoulder the effects become so small that the original and adjusted curve effectively merge.

Since Flare increases toe density its practical effect is a little like pre-exposure, boosting the shadow density in negatives. This is why ExpoDev boosts the EFS when using Flare to counteract this increased negative shadow value density to prevent overexposure (i.e. boosting EFS reduces the overall exposure, which brings the density down).

This is probably way more information than anyone wanted, but there it is - the short version at least.

david.jade

17-Mar-2012, 16:15

To me, this illustrates one of the advantages of incident metering: not having to pre-visualize. Almost everything in the subject is white, and there was nowhere obvious for me to place any of the zones. With this approach, the zones (many of which don't fall on a roman numeral if you know what I mean) took care of themselves.

From what I remember in talking with Phil at workshops, this was his point: accurate pre-visualization is tough to get right. BTZS Incident metering was developed to make it easier to get consistently good negatives that will be easier to print (both through contrast management and matching to your printing paper's ES). It makes some assumptions though, mainly that you want to render a scene realistically.

If however you want to apply your own interpretation to a scene, you can do that my modifying either shadow placement or highlight placement, effectively altering exposure and/or compressing or expanding contrast. Placing a certain subject at a certain zone was not the goal. Capturing a good negative that was easier to work with was.

The other part that most people leave out when talking about BTZS is that it is also about managing the translation of scene values to print values. This is more complicated than just placing a scene value on a certain zone in the negative via exposure and development. This is because printing papers have a curve too.

You can think of it like this: scene values are translated to negative density by way of the film's curve. Negative density values are translated to print values by way of the paper's curve. It's the combination of the two that tells you how a scene value will become a print value. This also means you can leverage the interplay between a film and paper curve to give a different interpretation of a scene, perhaps by expanding mid-tones using one combination of film/paper or compression them using another combination. Some combinations can expand or compress shadow values while others can compress or expand highlights or any combinations in between.

Plotter has a feature called the Matcher which graphs this out and lets you compare how different combinations of films and papers work together. You can see an example of that here, in the last screen shot on this page: http://btzs.org/Software/PlotterScreens.htm

Stephen Benskin

17-Mar-2012, 16:25

Since Flare increases toe density its practical effect is a little like pre-exposure, boosting the shadow density in negatives. This is why ExpoDev boosts the EFS when using Flare to counteract this increased negative shadow value density to prevent overexposure (i.e. boosting EFS reduces the overall exposure, which brings the density down).

This is probably way more information than anyone wanted, but there it is - the short version at least.

Thanks David for your response. I've written my own series of plotting programs including a 4 quad reproduction diagram so it's not more than I wanted. To tell you the truth, I've never been a big fan of combining the flare and film curve together. It's a construct that I believe gives a false impression of how flare works. It also eliminates important information that can only be obtained by using a camera image / flare curve. It's just my personal preference.

I take it the boosting of the EFS with the ExpoDev is only with anything above average flare. As you know, speed point, while determined using a no flare curve, has flare incorporated into its determination. Does the ExpoDev then basically adjust the EFS for the difference between average flare and the higher flare value?

With the development calculations, does it use a fixed flare model or some sort of variable flare model?

I'm curious as to know the exposure point, H, that you use to determine the flare value? Let me see if I can clarify the question some. A flare factor of 2, or 1 stop, means the doubling of the shadow exposure. That value is then added to the subsequent exposures along the film curve. Where that point is determined is important in correctly defining the value of flare. Let's say for a 125 speed film, it is determined at the speed point 0.8 / 125 = .0064 lxs. This value is then added to the all the points of exposure. But if flare is determined from the statistical average shadow exposure for a 125 speed film, 0.0032 lxs, this value will have quite a different influence. While both values technically have a flare factor of 2, they produce very different results. So at what point does ExpoDev determine the value for the flare exposure?

david.jade

17-Mar-2012, 16:54

I take it the boosting of the EFS with the ExpoDev is only with anything above average flare. As you know, speed point, while determined using a no flare curve, has flare incorporated into its determination. Does the ExpoDev then basically adjust the EFS for the difference between average flare and the higher flare value?

When the Flare amount is zero, ExpoDev just uses the EFS data as exported from Plotter (which has no Flare model applied since it was stripped before export). EFS points as exported by Plotter may be based on 0.1 over FB+F or may be based on the Approximate CI method. So in ExpoDev, Flare is just an additional compensation over what Plotter has determined for EFS at the calculated Average G of the scene (as metered).

With the development calculations, does it use a fixed flare model or some sort of variable flare model?
ExpoDev uses a very simple model of Flare when adjusting development. Basically, exposure is decreased by a small amount and development is extended by a small amount. We're talking about very small values here with the goal of controlling shadow density a little better while maintaining roughly the same contrast.

I'm curious as to know the exposure point, H, that you use to determine the flare value? Let me see if I can clarify the question some. A flare factor of 2, or 1 stop, means the doubling of the shadow exposure. That value is then added to the subsequent exposures along the film curve. Where that point is determined is important in correctly defining the value of flare. Let's say for a 125 speed film, it is determined at the speed point 0.8 / 125 = .0064 lxs. This value is then added to the all the points of exposure. But if flare is determined from the statistical average shadow exposure for a 125 speed film, 0.0032 lxs, this value will have quite a different influence. While both values technically have a flare factor of 2, they produce very different results. So at what point does ExpoDev determine the value for the flare exposure?

Since Plotter starts with a user-supplied Flare density value (0.02 is typical), for each film curve it finds the point that corresponds to that density on the curve. From that point it then knows how much additional exposure it takes to produce that density increase in a negative. This is the extra exposure given to each point in the curve to determine the new density that the combined exposure would yield.

In practice it gets a little more complicated as Plotter actually simulates a new set of curve points based on a fixed interval (1/2 stop I believe). It then uses this new curve as a sort of look-up table to translate the real curve points into the new exposure/density space, generating the final translated flare adjusted curve.

Shen45

17-Mar-2012, 18:54

http://www.kenleegallery.com/images/forum/Sink.png
Rangefinder Test, 2012
Mamiya 7, 150mm Mamiya N
TMY, Pyrocat HDC

I just gave your recommendation a try, and I have to admit that it worked much better than I had anticipated. This photo was made to test the accuracy of the rangefinder at medium distance. I got the high reading from the window itself, but I exposed for the shadow reading, as recommended in the BTZS book.

To me, this illustrates one of the advantages of incident metering: not having to pre-visualize. Almost everything in the subject is white, and there was nowhere obvious for me to place any of the zones. With this approach, the zones (many of which don't fall on a roman numeral if you know what I mean) took care of themselves.

Nicely executed Ken. Incident when used as Phil intended with BTZS is very simple. Many/most people cannot or won't entertain the idea that an incident meter can be used in any method other than a single reading pegged to their preconceived 18% or z5 reading of general light falling on a subject. Phil has taken a tool, the incident meter and created a metering method that looks at light quality more than anything else. Your question concerning a backlit subject is one I'm asked many times regarding BTZS and Incident metering - by ZS users - as if it cannot be done in any manner other than with a spot meter. Thanks for posting your results. For me the actual light [the anchor points of shadow and highlight] is the way I now see my photography. Everything else will fall where it should based on your film, developer and paper test combination.

This is a good discussion of BTZS. Thanks to all who are contributing and gaining some additional insights.

Steve

Stephen Benskin

17-Mar-2012, 18:58

When the Flare amount is zero, ExpoDev just uses the EFS data as exported from Plotter (which has no Flare model applied since it was stripped before export). EFS points as exported by Plotter may be based on 0.1 over FB+F or may be based on the Approximate CI method. So in ExpoDev, Flare is just an additional compensation over what Plotter has determined for EFS at the calculated Average G of the scene (as metered).

I'm probably not being very clear with my question. The example below shows the ratio between the camera exposure and speed point of 0.10 over fb+f (point B) in addition to where the average scene's shadows fall (point A). The speed point is approximately one stop above where the shadows fall. Average flare brings the shadows (A) up from to around the speed point (B). Now, if I understand your response correctly, speed data is imported into ExpoDev where it compensates the EFS for flare. The way I'm interpreting what you are saying is that the ExpoDev assumes the speed data is from a no flare model and any flare value input into ExpoDev will then affect the EFS. If this is correct, then ExpoDev is adjusting the EFS for flare, up to average flare, which has already been compensated for.

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What I'm saying is that the placement of the speed point Hm at a difference of 1.0 log-H from P (metered exposure point 8 / ISO) assumes flare as part of the speed equation as the below example illustrates using the standard exposure model for a 125 speed based exposure. In effect, the below example is essentially the exposure condition that the ISO black and white film standard assumes when determining film speed at the 0.10 over Fb+f speed point. If the ExpoDev assumes the addition of any flare on top of that, up to the value of average flare, then any compensation to the EFS would be compensating for double the effect of flare and under rate the film. Am I correct in assuming that when 1/2 stop of flare is input into ExpoDev, it will then adjust the EFS based only on that value?

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Bill Burk

17-Mar-2012, 19:05

The other part that most people leave out when talking about BTZS is that it is also about managing the translation of scene values to print values. This is more complicated than just placing a scene value on a certain zone in the negative via exposure and development. This is because printing papers have a curve too.

This is where the original Power Dial fascinated me, because the steps to make it involved some intense graphic arts knife work (which I could feasibly do given my graphic arts background). Then you expose some of your paper at varying times. The result is a real estimation of the tone for the exposure given the development. Amazing idea. Why I wonder if anyone ever made one of these...

Stephen Benskin

17-Mar-2012, 20:01

This is what I was talking about concerning where the value of flare is calculated. The example below has the standard model where a flare factor of 2 (1 stop) is calculated from the shadow exposure (0.0034) making it (0.0068). The other example calculates the flare value from just a little over the speed point (0.0068) making the shadow exposure (0.0098).

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These are the equations I used to calculate H for a one stop flare factor. In my program, a number of the values are variables.

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david.jade

17-Mar-2012, 23:56

The way I'm interpreting what you are saying is that the ExpoDev assumes the speed data is from a no flare model and any flare value input into ExpoDev will then affect the EFS. If this is correct, then ExpoDev is adjusting the EFS for flare, up to average flare, which has already been compensated for.

So I'm not sure I am following "which has already been compensated for."

Plotter's simulation model of Flare is only enabled when the user specifies a flare density value during analysis, which is applied to the curve's data points as I previously outlined. When exporting data, that flare simulation is always turned off so it is the raw EFS data either from 0.1 above FB+F or the Approximate CI method of speed point determination. So yes, ExpoDev always assumes that no flare model is in effect when it applies its flare compensation, because it knows that Plotter has exported the data without using its model of flare.

Neither Plotter nor ExpoDev present flare as stops, they both deal with flare as an average density that gets added, typically 0.02, which when translated to EFS adjustments in ExpoDev is a very small adjustment that is much, much less that 1 or even 1/2 a stop. It is the amount of exposure needed to reduce the negative density by that flare density amount. For instance with an EFS of 100, with a flare density factor of 0.02 added the EFS gets adjusted to only about 102. We're talking very small fractions of a stop.

What I'm saying is that the placement of the speed point Hm at a difference of 1.0 log-H from P (metered exposure point 8 / ISO) assumes flare as part of the speed equation

Now if you are saying that the fundamental method of determining the speed point via the ISO triangle has a built-in model of flare, then I guess so - ExpoDev is applying a flare compensation over that built-in amount. But I'm not sure I am following your reference to "the standard exposure model for a 125 speed based exposure" though.

Plotter's method of speed point determination just uses the standard model of speed point determination by (simulated) placing the ISO triangle for a curve with an average gradient of 0.62. Plotter interpolates a curve from the film data with a average gradient of 0.62 and then finds the speed point on that curve and assigns an EFS that the user stated as the ISO of the film (there's a little more to this that involves a calibrated personal reference point since not all films are the ISO they say they are and that has to be compensated for as well). Then Plotter finds the speed points for for each of the other curves and determines their EFS in relation to the found ISO point. It sounds to me that Plotter is using a different way of determining the EFS of the tested films from what you are doing.

However, back to what I think your question is: where does Plotter determine the exposure point, H, to be when it finds the adjustment to use for flare compensation. Plotter simply looks at the curve to find the FB+F density that equals the amount of flare specified, i.e. where the FB+F density is 0.02 typically. From that point it can then determine the amount of exposure needed to double the density from that section of the curve and thus knows what additional exposure amount will produce an increase in density of 0.02 for flare for that particular film and developer combination.

Bill Burk

18-Mar-2012, 07:25

...And also, Minor White invented BTZS. His "Zone System Manual, How to Previsualize Your Pictures" outlines "Short Cut Exposure-Development Calculations"

1. Take a meter reading off the palm in shadow
2. Place on Zone IV to set exposure
3. Take a meter reading off palm in sun
4. Development determined by difference in the two readings.
5-Zone difference N-2
4-Zone difference N-1
3-Zone difference N
2-Zone difference N+1

I exaggerated Minor White's contribution. It's not right to say he invented it.

It's more realistic to say he planted the seed for it.

Minor White clearly outlined a technique for two-incident-readings exposure and development estimation.

And this was carried further into a fully workable system by Phil Davis.

Kind of how John L Davenport's Constant Quality Prints inspired the Zone System in the first place.

Bill Burk

18-Mar-2012, 07:54

Neither Plotter nor ExpoDev present flare as stops, they both deal with flare as an average density that gets added, typically 0.02...

So the end-user who performs a "black box" test... directly inputs the density of the negative that they get reading the image of the box opening (which would be a clear spot without flare)?

Stephen Benskin

18-Mar-2012, 08:15

So I'm not sure I am following "which has already been compensated for...Now if you are saying that the fundamental method of determining the speed point via the ISO triangle has a built-in model of flare, then I guess so"

First, thank you for your time answering my questions. It's been very informative.

Yes, that is what I'm saying. Film speeds would be about a stop slower without flare.

But I'm not sure I am following your reference to "the standard exposure model for a 125 speed based exposure" though.

It's just the statistically average conditions - 2.20 log luminance range, 0.0 RD for highlight, Illuminance = 7680 fc , flare between 1 to 1 1/3 stops, using the standard exposure equation with q = 0.65. But as the ExpoDev doesn't use a camera image / flare curve, it wouldn't be applicable.

Plotter's method of speed point determination just uses the standard model of speed point determination by (simulated) placing the ISO triangle for a curve with an average gradient of 0.62. Plotter interpolates a curve from the film data with a average gradient of 0.62 and then finds the speed point on that curve and assigns an EFS that the user stated as the ISO of the film (there's a little more to this that involves a calibrated personal reference point since not all films are the ISO they say they are and that has to be compensated for as well). Then Plotter finds the speed points for for each of the other curves and determines their EFS in relation to the found ISO point. It sounds to me that Plotter is using a different way of determining the EFS of the tested films from what you are doing.

Slightly, the average gradient of 0.62 is a reference to the contrast parameters defined in the ISO standard, except that the standard actually uses a more limited log-H range,1.30, because it is concerned more with the gradient of the lower end. The log-H range used in determining the gradient can make a difference especially with long toed curves. If the contrast parameters are met, the fixed density film speed will have a good correlation with the fractional gradient method. The ISO standard is basically a simplified version of the fractional gradient method. Although one that only works at that specific contrast. For development less than or greater than the ISO parameter, using the fixed density method introduces a progressive error. In other words, the fixed density method of speed determination only is accurate for that one contrast. C.N. Nelson writes in Safety Factors in Camera Exposures "The fixed-density criterion tends to underrate films that are developed to a lower average gradient and to overrate films that are developed to a higher average gradient." As such he suggests "The fractional-gradient speed criterion (and its approximate equivalent, the simpler ΔX speed criterion described in Ref. 12) will continue to be useful as a supplement to the fixed-density speed criterion when an evaluation is desired of the effective picture-taking speeds of films that have been developed to average gradients higher or lower than the proposed standard average gradient." BTW, the "simpler ΔX speed criterion" reference is what the ISO speed standard actually uses. That's where the contrast parameters come from.

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Because of the inverse relation of the difference from the fractional gradient point to the fixed density point with the "average" gradient, film speeds using the fractional gradient / Delta-X method don't change nearly as much as with the fixed density method. This means that a negative processed normally will have a different overall density than one developed to a higher gradient even though their film speeds might be the same. As Jones observes, "From the standpoint of tone reproduction theory there seems to be no justification for the adoption of any value of density as a significant criterion of the speed of a photographic negative material. The primary function of the negative material is to record brightness [luminance] differences existing in the scene. Density, per se, has no significance as an indication of the ability of the photographic material to perform this function."

From a practical shooting standpoint the different speed values derived from the fixed density and the Delta-X speed methods aren't that big of a deal considering the variability of flare from scene to scene and that fact that film speeds were at one time about one stop slower than they are today without any detrimental effects (and ZS speeds are still there). It's more a question of accuracy.

Granted, BTZS is a large step or two above the Zone System, but it's still a system. I wrote my own programs because I didn't want to compromise on either exposure theory or tone reproduction theory. Plus, I didn't want to deal with all the made up BTZS terms. :)

david.jade

18-Mar-2012, 11:33

So the end-user who performs a "black box" test... directly inputs the density of the negative that they get reading the image of the box opening (which would be a clear spot without flare)?

Yes, if a user really needs to manage flare precisely they could perform a test to determine the amount of flare for their conditions, equipment, etc..

For me with modern lenses, I typically use the suggested value and it works just fine. I suspect that this is what most people do. Even during Phil's 5 day workshops testing flare was not something anyone did.

david.jade

18-Mar-2012, 11:48

First, thank you for your time answering my questions. It's been very informative.

It's been interesting for me too, I haven't really looked at the Plotter code in many years now. ExpoDev on that other hand, well that's been my life for the last 7 months or so getting it out there again. Still, much of the exposure calculation code is 8+ years old now too (as evolved from the Palm version).

Granted, BTZS is a large step or two above the Zone System, but it's still a system.

For me I've always taken a very pragmatic approach to using any system. The BTZS system (and the tools used) allow me to get negatives that are so much better than what I got with traditional Zone System testing, exposure, etc... with very little additional effort (all upfront). Things are just more consistent for me now.

Most would probably also think that as the author of the BTZS tools that I spend a lot of effort with film & paper testing but it's the opposite actually. I test once when materials change. In fact I used Phil's test data for years until Kodak changed some things. I find something that works and I get out and take as many photographs as I can. Tools like ExpoDev (and Plotter) just make me more efficient and free up my mind to concentrate on the image vs. the process.

blevblev

21-Mar-2012, 07:00

If you have an iPhone, don't bother with the Palm Pilot thing. Expodev has be rewritten for the iPhone, and is available on the app store. Search for 'BTZS expodev.' Maybe the author can't say anything, but I can.

:)

baachitraka

21-May-2012, 14:51

When taking low and high reading, always set the meter ISO to 100 initially. Once you determine the SBR using the BTZS, consult the EFS charts to set the film speed and take shadow reading and determine the exposure and use SBR to determine development times.

Thanks for the recommendations. I mentioned in my post that I am aware of the ExpoDev software, but I'm trying to grasp the fundamental concept. Meters with dials often behave differently than meters with numeric readouts, and explanations can be... ambiguous.

I actually have a Power Dial, and find that the exposures it recommends are at odds with what Phil Davis recommends on pp. 136 paragraph 2 of the latest edition of his book. In Appendix 5, he gives some instructions about its use, but there are some questions about which ISO to set, which remain unanswered. I get the impression that he was rushed by one reason or another, when adding that section to the book. For example, he tells you to use the box speed of your film - except 250 when shooting TXT, and 80 when shooting FP4. He doesn't explain why those films would be handled that way - and not others. Many people shoot those films at lower-than-box speed of course, but it's surprisingly inconsistent, considering how earnest and meticulous the bulk of his writing are.