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Eric Woodbury
20-Jan-2010, 14:37
I've been doing some film developer combo testing. Anybody have some clever way to do this? Usually I set up a set of targets (black, grey, white cards) in the sun and take a series of test images. Right now, all we have here is clouds and mud. Sometimes I image a step wedge. This has its moments, too, but doesn't really tell you what an image will look like. Lately, I have been imaging inside under lights, but I don't really have a lot of indoor space. I can calibrate out the tungsten shift.

What I'd like is some means to use an enlarger with a coldlight. Seems possible. I guess I could put a step wedge in the enlarger and a shutter on the enlarger, but I am worried about the light leakage and to some degree the color of the light, but I could plug up the holes and calibrate the color shift. It doesn't really tell me the quality.

It just may be that there is no one good answer, but I thought I'd ask what others are doing --- you are a clever bunch.

ic-racer
20-Jan-2010, 15:19
Actually, there are a lot of ways to do this.

You can contact the step wedge using the enlarger. This is a makeshift sensitometer. Use a glass to get it flat for best results. If you project it you don't know your values for the x-axis (unless you have an enlarging exposure meter). If you contact, then you x-axis values can be obtained by reading your step wedge with your densitometer.
You can also use a camera as a sensitometer by affixing the step wedge to a sheet of film (large format camera) and aiming at a uniform target. (to tedious for me, but some do it this way).

IF you are going to do routine testing, you can just buy a sensitometer.

Eric Woodbury
20-Jan-2010, 15:45
ic-racer

with 400 ASA film, do you use a shutter on the enlarger?

ic-racer
20-Jan-2010, 16:11
ic-racer

with 400 ASA film, do you use a shutter on the enlarger?

Before I got my sensitometer I used the digital enlarging timer set to something less than 1 sec. Set the aperture small, enlarger column high. You could use ND filters also.

Even with a sensitometer, you have to fiddle with the light intensity to match the film to the step wedge. Even more fiddling to fit a range of film speeds on the step wedge so you can do relative-speed comparison testing.

Maris Rusis
20-Jan-2010, 17:14
I test film, usually in the 8x10 format, by making a series of exposures from Zone 1 to Zone X by moving the dark-slide stepwise across the film for each exposure. My target is usually a white sheet evenly lit in sunlight.

In the darkroom I cut the film into four equal strips with each one bearing the ten step exposure sequence. Then all four strips go into the developer at once and get routine tray agitation. At regular intervals, say 2 minutes, 4, 8, and 16 minutes, I take a film strip out of the developer tray and put it in the stop bath. After 16 minutes I take all the film strips through the usual fix, wash, dry routine.

The end result is 10 exposures for each of four different developments. The data, plotted out in the usual D versus log Exposure format, give me four curves and everything I need to know about EI, and N-, N, and N+ development either directly or by simple interpolation.

Total cost: a sheet of film, some chemicals, and a couple of hours.

mikebarger
20-Jan-2010, 17:21
I just finished doing this with HP5, and Dektol 1:2 following Fred Picker's procedure.

Mike

sanking
20-Jan-2010, 17:34
What I'd like is some means to use an enlarger with a coldlight. Seems possible. I guess I could put a step wedge in the enlarger and a shutter on the enlarger, but I am worried about the light leakage and to some degree the color of the light, but I could plug up the holes and calibrate the color shift. It doesn't really tell me the quality.



Phil Davis' method of testing film was based on contact printing a step wedge to film using an enlarger. Get a copy of his book, Beyond the Zone System, and there is a good description of how this is done. I used an enlarger plus a Metrolux timer (which is based on light integration) and it worked perfectly for testing film.

One can also expose film with a sensitometer. They come up from time to time on ebay.

Sandy King

Tim k
20-Jan-2010, 18:38
I test film, usually in the 8x10 format, by making a series of exposures from Zone 1 to Zone X by moving the dark-slide stepwise across the film for each exposure. My target is usually a white sheet evenly lit in sunlight.


Maris,
I like your method. However, its making my head hurt, thinking about how you might be using your darkslide to do that. Are you simply exposing the entire sheet, for say zone 1, then move your darkslide it in a bit, and then stacking the additional time that would be required for say zone 2, and then 3 etc.?

percepts
20-Jan-2010, 19:59
Maris,
I like your method. However, its making my head hurt, thinking about how you might be using your darkslide to do that. Are you simply exposing the entire sheet, for say zone 1, then move your darkslide it in a bit, and then stacking the additional time that would be required for say zone 2, and then 3 etc.?

Start with slide closed. Open a little.

Give zone 9 exposure. (metered value opened up 4 stops)
move slide out a little more
Give zone 8 exposure (metered value opened up 3 stops)
move slide out a little more
Give zone 7 exposure (metered value opened up 2 stops)
move slide out a little more
Give zone 6 exposure (metered value opened up 1 stops)
move slide out a little more
Give zone 5 exposure (metered value)
move slide out a little more
Give zone 4 exposure (metered value closed down 1 stop)
move slide out a little more
Give zone 3 exposure (metered value closed down 2 stops)
move slide out a little more
Give zone 2 exposure (metered value closed down 3 stops)
move slide out a little more
Give zone 1 exposure (metered value closed down 4 stops)
move slide out a little more
Give zone 0 exposure (metered value closed down 5 stops)

as the darkslide is pulled exposing each strip of film, the first bit of exposure that strip is given is one stop less than it will finally receive via the accumulation of subsequent exposures so that it has in total 1 stop more exposure than it got on its first exposure.
So the very first exposure at zone 9 will end up with zone 9 + all of the exposures for zone 8 thru zone 0 which is equivalent to a zone 10 exposure.

Ken Lee
20-Jan-2010, 20:03
Sometimes I image a step wedge. This has its moments, too, but doesn't really tell you what an image will look like.

Here's a fairly straightforward method that will tell you what your images will look like.

http://www.kenleegallery.com/html/tech/testing.html

Tim k
20-Jan-2010, 21:27
Start with slide closed. Open a little.

Give zone 9 exposure. (metered value opened up 4 stops)
move slide out a little more
Give zone 8 exposure (metered value opened up 3 stops)
move slide out a little more
Give zone 7 exposure (metered value opened up 2 stops)
move slide out a little more
Give zone 6 exposure (metered value opened up 1 stops)
move slide out a little more
Give zone 5 exposure (metered value)
move slide out a little more
Give zone 4 exposure (metered value closed down 1 stop)
move slide out a little more
Give zone 3 exposure (metered value closed down 2 stops)
move slide out a little more
Give zone 2 exposure (metered value closed down 3 stops)
move slide out a little more
Give zone 1 exposure (metered value closed down 4 stops)
move slide out a little more
Give zone 0 exposure (metered value closed down 5 stops)

as the darkslide is pulled exposing each strip of film, the first bit of exposure that strip is given is one stop less than it will finally receive via the accumulation of subsequent exposures so that it has in total 1 stop more exposure than it got on its first exposure.
So the very first exposure at zone 9 will end up with zone 9 + all of the exposures for zone 8 thru zone 0 which is equivalent to a zone 10 exposure.

Thanks, but sorry, it still makes my head hurt.
Guess I'll have to get out my meter, and work the numbers.
Just seems like the first few would be way over.

Nathan Potter
20-Jan-2010, 22:11
Well, I use the dark slide technique on occasion, but slightly differently. I set up a 30X40 white matboard and block half with a white towel long ways. I use bright sun at a 45 degree angle to the matboard. I meter the white board side and close down 5 stops (under expose). Then I pull out the darkslide a half inch at a time using the same exposure for each of 10 steps. I adjust the aperture so that each exposure will be about 1 sec. so I don't have a shutter speed variable - (watchout for clouds). I develop the whole sheet - no cutting. The towel yields visual information about highlight and shadow textures. N+ and N- data is obtained with additional films in the chosen developer.

I'll use the more precise 20 step stouffer wedge taped to the holder for more precise sensitometric curve data. Actually 2 step wedges - one where the towel is imaged and one where the plain white is imaged. The wedge method is a bit more of a nuisance.

Nate Potter, Austin TX.

Stephen Benskin
22-Jan-2010, 15:16
The dark slide method sounds like it would have potentially many accuracy problems, not to mention intermittent exposure effects. Precise adjustments to the aperture and shutter speed are not really possible or repeatable, and small multiple exposures will have a different result than one complete exposure.

Sandy's suggestion of BTZS testing is the most accurate way to go for most.

jeroldharter
22-Jan-2010, 19:37
Do the BTZS test method. For ISO 100 film, use your spot meter and adjust the light on your enlarger to read EV4. Contact print a Stoufer step wedge on to your film for 5 identical exposures. Develop each sheet of exposed film for a different development time. The usual is 4 min, 5.5 min, 8 min, 11 min, and 16 min. Send the film off to The View Camera Store and for ~$45 they will examine the film with a sensitometer and send you graphs of all of the results e.g. N vs development time, N vs ISO, etc. Might as well do it right the first time.

If you plan to test very often or with many films, buy a used X-rite 810 densitometer but using the BTZS Plotter software makes everything very easy. But for $45 plus 5 sheets of film you have a solid start. You could spend weeks dinking around otherwise.

Bill Burk
23-Jan-2010, 00:05
I'd like to steer you away from shooting a step wedge or exposing on a sensitometer. Sure you will get lab quality results. But they won't be personalized to what you are shooting so they might not work for you. I recommend instead picking up a copy of Minor White's Zone System Manual. This is a little 110 page booklet. My second edition from 1963 has two slugs misplaced on page 43, otherwise the book is flawless. He tells you you two ways to go. One requires a densitometer and sounds a lot like what Maris Rusis and percepts are describing. Yes it is hard to wrap your mind around. But if you write it down and add the times it makes perfect sense. 1/30 sec + 1/30 = 1/15 and when you add another 1/15 it's roughly 1/8. Keep doubling. Don't worry about the exposure accumulation error. The low-end Zones don't get many cumulative exposures (for example 1/30 + 1/30 is going to be a good equivalent for 1/15 in most shutters). The high-end Zones are getting blasted with full seconds. If you make exposure mistakes, they will show up as points that don't make sense in your graphs. Write it out as a plan and it will be more a chore and less a brain-teaser. It is painstaking, when you start making test exposures you can rethink how much a sensitometer would improve your life. In the same book Minor White gives a visual match method where you don't need a densitometer to evaluate the results. You just paint a two-tone target (paint a sheet of plywood so one-half is middle gray and one-half is a full stop lighter gray) and shoot Zone 0 & I then push the darkslide halfway in and shoot Zone IX and X. Expose a few identical sheets and develop them for various times around recommended. Then the shot that prints all four quadrants is what you take for N. Whichever way you test, I strongly recommend you do the tests with your camera and lens and light (I have a hard time with daylight, the sun keeps moving and this can take a couple hours), your film, developer, paper and enlarger. You're looking for the speed of all the parts of your system, including camera and enlarger flare. This is not idealized and averaged conditions, it's your own specific conditions. The reason you will find your Exposure Index is not the same as the published ISO is you completely threw ISO out the window. You aren't even metering to ISO any longer. The reason your film can take a range of 10 stops is that you are developing it so that it does. The reason those 10 stops fit on paper is that you develop the film until it reaches the right density to do that. The part I enjoy these days is not that everything works perfectly, because it still doesn't. But when something goes wrong, I am only one paper grade away from where I wanted to be. Ken Lee, your method sounds like distillation of a lot of experience. Sounds like Fred Picker might have shown you his barn and woodpile standard. Would love to hear more stories.

Bill Burk
23-Jan-2010, 00:25
On the other hand, now that I think about it... Stouffer scale, enlarger, EV4, develop, measure. Sure sounds easier.

Stephen Benskin
23-Jan-2010, 02:59
The "personalized" testing procedures most people use have many variables and are prone to experimental error. You are testing too many factors to be able to understand what controls or influences what. In order to do a proper test, you have to know what you are testing for and be certain there are no unwanted influences. In my opinion, the best way to test is to split up the tests so that you can be sure what the tests results actually reflect. Test the film and developer with a sensitometric method. A step tablet eliminates flare from the process. You can later factor in flare, but the problem with testing with the camera is that flare can't be measured and it varies with the luminance range and tone distribution of the scene. You have known density values unlike testing through a camera. And it's easier to minimize experimental error and unwanted variables. If you want to test the film and developer, do a test for them. After you get your results, bring in your equipment and do some practical shooting.

Also, before throwing out the ISO speed, you should first understand what it's all about and how the testing you are doing relates to it. Many tests use very different parameters which makes it impossible to compare the two. Knowledge is your best tool.

I've found the White book to be somewhat schizophrenic. The later editions are split between the semi-mystical writings of White and a section on sensitometry written by Richard Zakia and added in later editions. I haven't studied the book, but I recall a number of contradictions between the two sections.

There are two books that are really helpful primers for sensitometry. Sensitometry for Photographers by Jack Eggleston and Beyond the Zone System by Phil Davis.

Steve

ki6mf
23-Jan-2010, 05:17
The quick explanation came from Gem Singer in Texas. there is a step by step instructions in the second URL

http://www.largeformatphotography.info/forum/showthread.php?t=56334

Aim the one degree spot at the darkest area in the scene where you still want to see some detail. Close down two stops.

You have just placed the shadow area in Zone III.

That's usually the proper exposure for the scene.

Now, aim the spot at the brightest area in the scene.

If it's a five stop range between the darkest and brightest reading, use normal development.

Less than five, increase development.

More than five, decrease development.

No need to take a whole series of meter readings and average them. That's defeating the purpose.

Just make certain that you have given enough exposure to get some detail in the shadows. Then, develop for the highlights.

That's the Zone System in a nut shell.

For a Step by step guide to exposure and film speed index calculation use the Film Speed Test and Developing Test from Jerry Orabona Photography

http://www.jerryo.com/teaching.htm

sanking
23-Jan-2010, 07:25
I'd like to steer you away from shooting a step wedge or exposing on a sensitometer. Sure you will get lab quality results. But they won't be personalized to what you are shooting so they might not work for you.

This is just pure nonsense. In fact, testing with BTZS type procedures gives you far more personalized data than any other common form of testing out there. The major purpose of BTZS testing is to produce data that allows you to match your exposure and development to your printing process, whatever it may be.

I don't criticize the methods that others use to test their film but there is no doubt but that BTZS type testing is much more efficient than other methods of zone system, and it provides a vast amount more data that can be used to personalize your working methods.

Sandy King

jeroldharter
23-Jan-2010, 08:22
...
I don't criticize the methods that others use to test their film but there is no doubt but that BTZS type testing is much more efficient than other methods of zone system, and it provides a vast amount more data that can be used to personalize your working methods.

Sandy King

I've tried different systems over the years, including the non-densitometer approaches, and they worked pretty well. I found the BTZS too much to digest for my level at the time (I was wrong though!). It was because of the other approaches that I ended up with BTZS. Once you use that system there is no going back. Also makes it very easy to test more than once. You can do it all in the darkroom with any film/developer (or paper/developer) combination.

But it is a commitment because ideally one would have the Winplotter software and the ExpoDev for Palm software which some might find to be a clumsy extra step in the field. I have never figured out how to use the little slide rule card for exposure. As an aside, how do people use BTZS without a Palm or slide rule?

sanking
23-Jan-2010, 08:57
But it is a commitment because ideally one would have the Winplotter software and the ExpoDev for Palm software which some might find to be a clumsy extra step in the field. I have never figured out how to use the little slide rule card for exposure. As an aside, how do people use BTZS without a Palm or slide rule?

I generally don't use the Palm ExpoDev software in the field. If there are a number of complicating factors such as reciprocity effect, filter compensation, magnification compensation, etc. I will generally pull it out to test my own calculations, but for most scenes I just figure the SBR by taking a reading in the shade and in full light, expose for the shadows and then mark my film holder for the SBR condition noted.

For my personal use it is in the efficiency of the film testing that BTZS really shines. People who have limited their film testing to traditional zone system methods really don't know what they are missing.

Perhaps I should give the usual caveat. True, film testing and technical aspects do not replace or substitute for vision. But they allow one to control and shape his/her vision.

Sandy

nolindan
23-Jan-2010, 11:42
If you want to contact a standard 0-3OD step tablet on to film, using an enlarger as a light source, a starting exposure exposure might be:

Meter the back of a sheet of photographic paper and adjust the lens aperture so the meter reads 1 second/f4.0/ASA 100 (or 4 on a Pentax digital spot);
Expose for one second if exposing ASA 100 film;
Adjust time and/or aperture for other ASA's;
Stop down to increase time if you are using an analog timer.

This should give clear film on the darkest step of the tablet with a slight increase in density in the next step or two.

The above are for a tungsten light source and may need adjustment with a cold-light head. Any light source will work: load a photoflood reflector with a low wattage bulb and aim it at the ceiling.

As always: YMMV and advice worth price charged.

If you do contact a step tablet on to film please post the exposure you used for the best result.

ic-racer
23-Jan-2010, 13:19
Seems like people have different views as to what 'testing' involves.

The main reason I would make a step wedge contact is to answer the question "how long do I process this film"

That question needs to be answered by everyone and how you do it doesn't make any difference, as long as you are happy with your prints.

In my case I 'reverse engineer' a film and development time combination that produces good prints. I get the gamma of that combo and when I want (or am forced into it by limited availability) to use an 'unknown' film, I run a few strips to see how the unknown film responds. This gives me a good starting point.

Bill Burk
23-Jan-2010, 13:39
Steve Benskin and Sandy King pointed out a major flaw in my argument to avoid step wedge exposure on an enlarger. I concede that too many variables spoil the scientific process.

I was upset when my tests under Tungsten gave me a lower film speed rating than I would have gotten if I had done my tests outside.

I was also upset that my results with an uncoated Tessar and ancient Compur shutter were not as expected.

So I resolved to test my whole system.

Now as I concede my earlier major flaw, I would like to suggest that it is not total nonsense but recommend at least one sanity test of your whole system before you go into the field. If you have scientifically eliminated your other variables, this might give you a single "system factor" to apply.

I will try BTZS.

How do you account for the difference between enlarger light source and Daylight?

I don't think I am wrong about the validity of speed testing. You can't take the manufacturer's ISO into the Zone system.

I believe that once you start developing to exposure range, you are no longer developing to ISO. Your first departure is you take a different B+F target. Your next departure is you develop your highlights to a density of your own selection.

This does not invalidate the simplified "Zone System in a nutshell" method above. I believe it will work superbly. In that simple method you use the manufacturer's ISO and place shadow on Zone III. In a Zone system speed test by Picker/Adams/White etc, you would find your own EI. It is going to be lower than manufacturer's ISO. You would place your important shadow on Zone II. With a lower EI than manufacturer, placing the shadow on Zone II sounds to me like the same thing placing the shadow on Zone III with the manufacturer's ISO rating.

I still highly recommend the White pamphlet-sized book from 1963. With a two-tone target and tests that he describes in 3 pages, you can find your film speed without a densitometer. You don't have to read and understand the whole book. His esoteric comments about art can be set aside when you are doing the tests.

Stephen Benskin
23-Jan-2010, 14:21
[
How do you account for the difference between enlarger light source and Daylight?

That's a good question. This is one of the many variables I referred to earlier. The ISO standard specifies the color temperature for the light source for that very reason. Don't forget both enlarging and daylight have different color temperatures too. You have incandescent and cold light for enlargers, and open shade, sunlight, overcast, and variable clouds with exterior shooting. Most ZS photographers use open shade, which is only skylight, and that is rather blue. Not only can the different color temperatures affect the film's response but it can also affect the meter's.



I don't think I am wrong about the validity of speed testing. You can't take the manufacturer's ISO into the Zone system.

I believe that once you start developing to exposure range, you are no longer developing to ISO. Your first departure is you take a different B+F target. Your next departure is you develop your highlights to a density of your own selection.

This does not invalidate the simplified "Zone System in a nutshell" method above. I believe it will work superbly. In that simple method you use the manufacturer's ISO and place shadow on Zone III. In a Zone system speed test by Picker/Adams/White etc, you would find your own EI. It is going to be lower than manufacturer's ISO. You would place your important shadow on Zone II. With a lower EI than manufacturer, placing the shadow on Zone II sounds to me like the same thing placing the shadow on Zone III with the manufacturer's ISO rating.

To properly explain the strengths and weakness of both systems would be rather daunting to work through, but suffice it to say that what we have are two different approaches to testing and two different goals. You can't really compare reversal with B&W negative because the desired results and testing parameters are different. With reversal the midtone and highlight reproduction is paramount, and with negative film it is the shadows. Reversal film speed is determined in the midtones and negative film in the shadows. In a way, it's like that with ZS and ISO testing.

In 1960, the ASA film speed standard changed. The new standard eliminated part of a safety factor thus increasing film speeds by one stop. The idea was that better lenses and meters eliminated the need for such a safety factor. The increased use of smaller formats with the longer printing times and loss of sharpness and increased grain with denser negatives was also a deciding factor. According to earlier psychophysical testing, it was determined that excellent images are producible for a number of stops over the minimum exposure necessary to produce excellent images. In other words, there are in fact a few stops of overexposure latitude possible without image quality loss. So, the change in the standards couldn't have been based solely on improving the quality of the reproduction because there wouldn't have been much. Therefore, we can conclude there's really no practical difference between the quality produced when films were one stop slower and the quality produced with today's speeds.

Now, consider that the Zone System was developed before 1960. Adams had to have used the ASA speeds to compare his method to as he was developing the ZS testing method. As he tested different methods, he probably referred to the scientifically determined method of the ASA standard as the source to compare whether his current method's results would be in agreement. After all, he does use the fixed density of 0.10 over Fb+f as the speed point (the concept of a fixed speed point and whether the exposure is supposed to fall at the speed point or that the speed point is only the place to determine the film speed is a complex and interesting topic - for another time). When the ASA standard changed in 1960, the Zone System method didn't. That means for film testing today, the ISO and ZS testing methods are looking for two different speed values. As we know about the images produced with the old ASA and current ISO speeds, both systems produce quality results. So it is with ZS and ISO, two different systems that both produce quality results.

It's possible to extrapolate a very freeing concept from that those facts. Exposure is just about giving the film enough exposure to produce a quality print and negative densities aren't locked into specific print densities. There isn't an exact density for Zone III. As long as you have recorded the shadow detail, where Zone III falls on the curve, it will have approximately the same relationship to the other tones for any exposure above the minimal amount required. So, exposure doesn't have to be exact, you just need to record the range of scene luminances on a usable part of the film curve. Then you can adjust the printing exposure to place them where you want them. We can therefore conclude there isn't a rigidity to exposure that many seem to believe, and that is freeing.

Steve

AJ Edmondson
23-Jan-2010, 15:54
I have to agree with Sandy in that, in my experience, the BTZS "procedure" seems to provide very concise data and, compared to other test methods I have used, is the least "unwieldy." I really got "wrapped around the axle" in my desire to satisfy my OCD a few years back and bought the whole package - plotter/matcher software, Palm Pilot, etc. After working with the system for a while I simply evolved to using the data to determine my exposure and development, rather than using the Palm Pilot. In speaking with Fred Newman at "The View Camera Store" he once indicated to me that the "Zone System" approach was not the favored usage... the primary intent being centered around the incident light approach described in "Beyond the Zone System." Obviously there are less "interpretational issues" arising from assigning zone values which way be quite exaggerated.
At any rate I find the system (with the software which eliminates the time-consuming drawing of curves) works quite well with a minimum of testing.

Maris Rusis
23-Jan-2010, 16:20
The dark slide method sounds like it would have potentially many accuracy problems, not to mention intermittent exposure effects.

In practice the potential accuracy problems in "dark-slide" testing are negligible compared to uncontrollable variables in the field; changing light, uncooperative subject matter, non-linear light-meter, wind, cold, rain, that sort of thing.


Precise adjustments to the aperture and shutter speed are not really possible or repeatable, and small multiple exposures will have a different result than one complete exposure.

My shutter speeds run within a few milliseconds worth of repeatability every time I set them. And I know what they actually are as opposed to what is marked on the shutter speed dial.
The same with aperture settings. I set them as accurately in testing as I do in shooting. Any finer than that does not deliver a result I can translate into actual camera use.

Every time I check I find there is no significant intermittency effect with multiple exposures on film except at very high frequencies (thousands of exposures per second!) or at low light levels where reciprocity failure starts to bite.

There are advantages in testing actual cameras, lenses, and film in front of physical subject matter under the same lighting conditions as one will use for shooting. The biggest plus is the way mystery variables like "flare factor" get calibrated out of the system.

The down side of real-world testing, not BZTS, is that one ends with a highly personal set of numbers, odd shutter speeds, bent f-stops, effective EI values, quirky development shuffles, that work perfectly but are of no use to anyone else.


Sandy's suggestion of BTZS testing is the most accurate way to go for most.

I agree, if you want laboratory standard objective data that photographers can trade among themselves then BTZS is the way to go. But given a "bad" camera, "bad" lens, "bad" film, or "bad" subject matter, with the light sliding away at the end of a "bad" day neither practical testing or BTZS data is much salvation.

Stephen Benskin
23-Jan-2010, 18:56
There are advantages in testing actual cameras, lenses, and film in front of physical subject matter under the same lighting conditions as one will use for shooting. The biggest plus is the way mystery variables like "flare factor" get calibrated out of the system.

I'm going to have to disagree with you on that point. 80% of flare comes from the subject. Most testing via the camera use a single toned test subject which produces very little flare. Flare also varies from subject to subject. It tends to increase with higher subject luminance ranges and decrease with shorter luminance ranges. It also varies within the same luminance range depending on tonal distribution. Plus, it is incredibly hard to measure. By eliminating all flare through contacting a step tablet, you are able to deal exclusively with the film/developer combination. A flare factor is than reincorporated into any interpretation of the curve and when deciding any actions to be taken, such as in development determination, and speed determination.

I've attached a curve showing how differing amounts of flare affect the shadow placement. I make a flare box as described in BTZS and place different toned squares around the "black hole" opening of the box and photographed it using the same settings. If no flare existed within the camera system, the opening showing the inside of the box should be at film base plus fog. As you can see on the curve, that wasn't the case. The resulting density difference between a black surround and a white surround is 0.09 and a log-H difference of 0.39 or around 1 1/3 stops of exposure. When doing a speed test, how can anyone be certain the amount of flare influencing the test and consequently, the accuracy of their results?



Photographers can trade among themselves then BTZS is the way to go. But given a "bad" camera, "bad" lens, "bad" film, or "bad" subject matter, with the light sliding away at the end of a "bad" day neither practical testing or BTZS data is much salvation.

I don't see it that way. Earlier I suggested sensitometric testing of the materials and then field testing them. The personalize to one's own equipment argument is one that seems to make common sense until you begin to carefully analyze it. Even if it were the best way to factor in all the materials, to really accomplish that, you would have to do tests for all of the lenses at each shutter speed and f/stops and the f/stop should be adjusted to T/stops. Nobody does that. When I mentioned accuracy for apertures, I was mostly thinking about attempting to accurately place the settings. 35mm cameras don't have 1/3 increments. How accurate can testing be with that?

Sensitometric testing isn't isolated from the real world results. Far from it. Everything is based on carefully evaluated real world tests, then a mathematical model is made that reflects those findings. Yes, everything tends to be based on the average of the conditions studied, average lens flare, average scene luminance range, etc. Still, there is always a bell curve for each showing the range and frequency of variance. I can't remember who said it "The universe is only truly knowable through math." As is the technical aspects of photography.

There's also a greater amount of information obtainable from sensitometric testing and the data can be utilized in a number of ways not possible with other methods. I have to admit that you aren't utilizing the full potential of sensitometry when you only use the film curve or paper curve alone. Real insight into the process and greater control can be gained when you start combining the information. Ultimately, a four quadrant reproduction curve offers the entire photographic process from original subject to camera/flare image to negative curve to paper curve to reproduction curve in graphic form. This would be a truly daunting task if it weren't for computers. I've attached an example of a four quadrant reproduction curve. BTZS is like any "system", it tends to simplify and gloss over certain details and concepts, but it is clearly written and free of bad information and BS.

Steve

Chuck P.
23-Jan-2010, 20:14
I've attached a curve showing how differing amounts of flare affect the shadow placement. I make a flare box as described in BTZS and place different toned squares around the "black hole" opening of the box and photographed it using the same settings.

Stephen,
You say that you photographed them using the same exposure settings----what method of metering for the exposure did you use----spot, incident, wide area reflective? Just curious.

Chuck

Andrew O'Neill
23-Jan-2010, 20:15
BTZS method is a great way to learn a ton of info about your film and developer combination. And you can get there with minimal waste of film. I use BTZS (I don't use that palm pilot thingy), but do not expose under an enlarger. I use Gordon Hutchings' Zone Board. Testing is indoors under consistant lighting (daylight balanced bulb). I graph all my data by hand and a rubber, flexible ruler. I've been doing it this way for over ten years and have been quite happy...

Stephen Benskin
23-Jan-2010, 20:21
Stephen,
You say that you photographed them using the same exposure settings----what method of metering for the exposure did you use----spot, incident, wide area reflective? Just curious.

Chuck

Spot metered a gray card. After the flare box tests, a sensitometric exposure was made on the same roll of film and everything was processed at the same time.

Chuck P.
23-Jan-2010, 21:05
Spot metered a gray card.

Since flare is so variable and thus hard to measure and since flare is a result of light passing through glass, which most are mitigated by a coating(s) where desired-----to what degree of flare, I wander, must the glass of a spot meter lens also be experiencing flare?

Wouldn't the flare occurring as a result of spot metering through glass during the type of testing that us ZS testers do somewhat mitigate or somehat neutralize the effect of flare on the resulting negative densities?

Seems the needle in my Pentax V spot meter must also be influenced by flare to some degree and therefore, this influence would then be accounted for in my characteristic curves.

Just curious?

Chuck

nolindan
23-Jan-2010, 22:01
Enlarger & Step Tablet testing sub-thread

Exposing a step tablet under an enlarger gives you the HD curve for the film. It says little useful about the EI. The amount of exposure isn't material except that the entire HD curve is captured somewhere on the image of the tablet. Likewise the difference between tungsten and daylight has no relevance as all the steps in the wedge exposure are exposed with the same color of light.

Since it is a contact print there is no flare - it isn't a system test but a test of the film and the film alone.

For measuring camera flare the best method is a Sinar with a metering back -- but that only gives the flare in a Sinar, not most people's idea of a field camera.

Stephen Benskin
24-Jan-2010, 00:26
Since flare is so variable and thus hard to measure and since flare is a result of light passing through glass, which most are mitigated by a coating(s) where desired-----to what degree of flare, I wander, must the glass of a spot meter lens also be experiencing flare?

Wouldn't the flare occurring as a result of spot metering through glass during the type of testing that us ZS testers do somewhat mitigate or somehat neutralize the effect of flare on the resulting negative densities?

Seems the needle in my Pentax V spot meter must also be influenced by flare to some degree and therefore, this influence would then be accounted for in my characteristic curves.

Just curious?

Chuck

The idea of flare affecting the spot meter helps support the argument for sensitometric testing IMO. It's one more variable that you can't control or predict.

Flare is involved with spot meters. It's always best to shade them, but in terms of how much flare affects the meter, it shouldn't be too much considering flare has little influence at the midpoint. Spot meters also have internal baffles and they only see a very limited area. In high flare situations, there is probably a certain amount of flare influencing the spot meter, but for the average camera lens, it's 1 1/3 stops in the shadows. By the midpoint, it's 3%. Look at quadrant one of the four quadrant reproduction curve example. That camera image curve has one stop of flare which is what the standard exposure model and film speed is based. The straight no flare curve has the shadow exposure at 0.0034 and the flare curve shadow at 0.0068 which is twice as much or one stop. The camera image/flare curve is calculated for 125 speed. For anyone who knows about the ISO speed equation - 0.8/0.0068 = 117. This indicates that a one stop flare factor will bring the exposure slightly about the speed point for 125 speed film.

Yes, film speed would be a stop slower if not for flare. That's why the speed point in the ISO standard has the speed point only 1.0 log-H (3 1/3 stop) below the metered exposure while the average shadow falls 1.2 log-H (4 1/3 stops). One stop of flare brings it back up. As average flare is more around 1 1/3 stops, there is an additional 1/3 stop safety factor. Again look at the four quadrant reproduction curve. The straight line in quadrant 1 represents the camera image without flare. See how far down the shadow falls. The other curve is the camera image of the subject affected by flare. Notice how the flare brings the point of exposure up to the film's speed point. I've attached a two quadrant reproduction curve showing the relationship between ZS testing.

The ZS rounds the 7 1/3 stop range down to 7 stops, making the shadow placement 4 stops down from the metered exposure point. Zone System testing is done with a subject that produces minimum flare. As the ZS testing doesn't factor in flare, the preponderance of EIs from film speed testing are 2/3 of a stop below the ISO speed. Ever wonder why so many people who do personalized speed tests to factor in their own specific equipment almost universally produce film speeds 1/2 to 1 stop slower than the ISO speed? That is one of the reasons, and the earlier pre and post 1960 film standard explanation is another (both actually work together and are interchangeable).

Steve

Bill Burk
24-Jan-2010, 00:27
Eric, did you ever get the answer you were looking for?

The high-tech BTZS method means only a little work for you and gets you a lot of information. If you want, they can send you film that already has a step wedge exposed on it.

Then there is the low-tech Zone System that is a lot of work and you have to interpret the results.

Steve, BTZS' founder, Phil Davis, omitted a key fact in his criticizm of the Zone System. In the article "In defense of testing," he argues the Zone System is not scientific because the visual match method of print evaluation is subjective. He is suspiciously silent that Minor White describes a densitometer method.

So I am not going with BTZS now.

I will contact through a step wedge, though. Eliminating variables is good.

Then I'm still planning to use a fixed speed point and I will still graph my development time curves on paper and select N times according to Minor White's pamphlet, densitometer method. And I will still base my exposure by spot-shadow placed at Zone II.

Eric, The BTZS method of metering is different.

Stephen Benskin
24-Jan-2010, 00:39
Exposing a step tablet under an enlarger gives you the HD curve for the film. It says little useful about the EI. Likewise the difference between tungsten and daylight has no relevance as all the steps in the wedge exposure are exposed with the same color of light.


Your right that testing with an enlarger can only give you relative film speeds, the light source has little influence. That's why I like to use a sensitometer with a calibrated exposure value. That way I can produce effective film speeds.

But people doing in camera speed tests can have the results influence by color temperature, and not just by the spectral sensitivity of the emulsion, but the spectral sensitivity of the light meter's photo cell can have a rather large influence. Most of the disagreement between different meters can be attributed to different materials used for the photo cell which have different spectral sensitivities. A good test to check your meter is to take a red filter, meter a value from a scene without the read filter and then with the red filter. Check the difference against what the filter factor should predict. Changes are there can be around a stop difference. A strong red sensitivity could mean a weak blue sensitivity. That just might have an influence when testing under skylight.

Steve

Stephen Benskin
24-Jan-2010, 01:04
Then I'm still planning to use a fixed speed point and I will still graph my development time curves on paper and select N times according to Minor White's pamphlet, densitometer method. And I will still base my exposure by spot-shadow placed at Zone II.


Bill,

That sounds like good solid sensitometry to me.

Now, here's something you might find interesting. Speed determined from the fixed density method is only accurate for normal processing. According to C.N. Nelson, Safety Factors in Camera Exposures, Photographic Science and Engineering, vol 4, n 1, Jan-Feb 1960, "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." It's kind of a fun monkey wrench type of concept. Nelson suggests, "the fractional-gradient speed criterion (and its approximate equivalent, the simpler Delta X speed criterion) will continue to be useful as a supplement to the fixed density speed method criterion when an evaluation is desired of the effective picture taking speeds of films that have been developed to average radients higher or lower than the proposed standard average gradient." Unfortunately, this concept and underlying element of the ISO standard has been overlooked by popular photographic sources.

Steve

sanking
24-Jan-2010, 06:59
How do you account for the difference between enlarger light source and Daylight?
whe
I don't think I am wrong about the validity of speed testing. You can't take the manufacturer's ISO into the Zone system.



In film testing with an enlarger with tungsten light source most people use a light blue 80A filter to approximate daylight shooting conditions. This tends to give a more realistic rendition of film curve as they would appear in daylight conditions. I now test film with an EG&G sensitometer which uses a daylight balanced flash unit as the exposure unit.

In most cases the manufacturer's ISO rating of a given film is correct. However, the Winplotter program that is used with BTZS can be adjusted for personal speed point (PSP) in one of several ways. One way is to compare the results of a given film/developer combination with those of a combination known to give box speed, Delta 100 in D76 1:1 for example, or we can simply modify our PSP based on shadow density of actual field work.

In testing hundreds of films over the years I have found very few cases where the ISO rating of the film was incorrect. The EFS at which you expose film in practice is a different matter as it is determined by method of metering, accuracy of aperture and shutter, and developer, dilution and type of agitation.

Sandy King

Chuck P.
24-Jan-2010, 10:02
[QUOTE]............for the average camera lens, it's 1 1/3 stops in the shadows.

If you are trying to tell me that my lens is, on average, putting 1 1/3 stop more density in my shadow placements due to flare, then, well, I can only tell you that my subsequent densitometer readings of those shadow placements I'm making, don't agree. I believe, in my case anyway, that any flare density you are suggesting that is really in my shadows, thus reducing my negative density range, is theoretically insignificant, both by visual account on the surface of the print as well as from densitometer readings. Meaning it does not seem to be apparent enough to cause me any concern in printing my shadows, it apparently is insignificant enough to be easily printed "through" without any special effort.----I'm confident it is not adversely affecting (in actual exposure of the scene) the negative density range that I test for i.e., exposing the step tablet in the camera using daylight, determining the EI, then determining the "normal" development time, and other times.

I guess it makes for some enlightening bits of information when it comes to discussing exposure and development theory, but IMO, even the less intellectual brand of testing that you apparently believe is found in the ZS holds its own very well. Not that I'm accusing you of ZS bashing, just that there is a general sense from me reading your posts that you feel that ZS testing leads to not as good photographic results. It is just not the case, IMO.

Like SanKing said earlier, I would not discount or criticize other methods (I have no reason to do that)---------but at the same time, I also do not believe it is more well equiped to lead the photographer to his ultimate goal, just different.

Put a very "fine" fine art b&w print by AA (or anyone else for that matter that does ZS testing!) next to a very "fine" fine art b&w print from a photographer using BTZS, who really cares about the efficacy of the photographer's testing? Not me and I'll go out on a limb here, probably not most. I would only care that they were both analog :D

Chuck

sanking
24-Jan-2010, 10:45
Steve, BTZS' founder, Phil Davis, omitted a key fact in his criticizm of the Zone System. In the article "In defense of testing," he argues the Zone System is not scientific because the visual match method of print evaluation is subjective. He is suspiciously silent that Minor White describes a densitometer method.
Then I'm still planning to use a fixed speed point and I will still graph my development time curves on paper and select N times according to Minor White's pamphlet, densitometer method. And I will still base my exposure by spot-shadow placed at Zone II.

Eric, The BTZS method of metering is different.

A few points.

First, BTZS is not a rejection of the zone system. In fact, the words means beyond the zone system, and the "beyond" is primarily about the greater use of sensitometry that reflects the fact that measuring instruments such as densitometers are much more widely available today than at the time the zone system was introduced. I personally believe that if these instruments had been more widely available in the day of Ansel Adams he would have used, and promoted, sensitometry in the application of the zone system.

Second, EFS can be plotted with the Winplotter program using either a fixed density method of 0.1 over B+F or an approximate CI. If you load a set of curves you can switch between the two methods and quickly see how the two methods return different EFS values depending on time of development.

Third, most photographers who use BTZS tend to meter with the incident system that is based on subject brightness range. However, traditional zone type exposure determination with spot reflection metering is part and parcel of of BTZS. Both methods of metering, with pros and cons, are described thoroughly in Davis' Beyond the Zone System, and the Winplotter program, which Davis wrote early on for MAC computers, is capable of returning either SBR of N values depending on user choice.


Sandy King

Chuck P.
24-Jan-2010, 11:41
Second, EFS can be plotted with the Winplotter program using either a fixed density method of 0.1 oer B+F or an approximate CI. If you load a set of curves you can switch between the two methods and quickly see how the two methods return different EFS values depending on time of development.

This is cool, I would like to check into the Winplotter program. Is it expensive?

sanking
24-Jan-2010, 11:55
This is cool, I would like to check into the Winplotter program. Is it expensive?

The View Camera appears to have it for sale for about $60.

http://www.viewcamerastore.com/product_info.php?cPath=27_75&products_id=55

BTW, the current version of Plotter is for PCs, even though it was originally written for a MAC. You can of course run it on a MAC with Windows emulation but I just devote an IBM Think Pad to it.


Sandy King

Stephen Benskin
24-Jan-2010, 12:56
[QUOTE=Stephen Benskin;551994]

If you are trying to tell me that my lens is, on average, putting 1 1/3 stop more density in my shadow placements due to flare, then, well, I can only tell you that my subsequent densitometer readings of those shadow placements I'm making, don't agree. I believe, in my case anyway, that any flare density you are suggesting that is really in my shadows, thus reducing my negative density range, is theoretically insignificant, both by visual account on the surface of the print as well as from densitometer readings. Meaning it does not seem to be apparent enough to cause me any concern in printing my shadows, it apparently is insignificant enough to be easily printed "through" without any special effort.----I'm confident it is not adversely affecting (in actual exposure of the scene) the negative density range that I test for i.e., exposing the step tablet in the camera using daylight, determining the EI, then determining the "normal" development time, and other times.
Chuck

Average flare doesn't adversely affect the film. It can be beneficial. It increases film speed and reduces processing time. Lens coating didn't eliminated flare. It just reduced it. The average flare was around two stops before lens coating. Lenses with more elements will have more flare too. The 1 1/3 value for flare is considered standard for 35 mm users. As this is a large format forum and as large format lenses have fewer elements, their flare is lower - around 1 1/4 stops.

Flare is hard to measure because it has to be measured at the film plane and most people don't have the tools. I'm sure many have seen the example of Kodak's graphic representation of typical tone reproduction that I have attached. While they are using a smaller flare factor .25 you can see the difference between the Subject on top and the Optical Image below it.

As I pointed out on another thread, determining an average gradient for normal is based on three variables - the desired negative density range as determined by the paper's log exposure range which you plan on printing with, the scene luminance range, and a flare factor. It basically Rise over Run. By playing with the numbers, you can get the proper average gradient value to fit the paper's LER without seemingly factoring in flare.

Chuck has posted an example curve on another post. It has as the desired negative density range of 1.20. This value has been supported in many books. According to the older standards, the mean for the grade two LER is 1.05. The statistically average scene is 7 1/3 stops (2.2 logs). Many have rounded it to 7 stops (2.1 logs). Average flare is 1 1/3 stops (.40). Plugging them into the equation, we get:

NDR / LSLR - Flare = CI or average gradient

For NDR 1.20: 1.20 / 2.1 - 0 = .57
For NDR 1.05: 1.05 / 2.2 - .4 = .58

Both approaches produce the same result; therefore, both negatives produced will have the same negative density range for the same scene. So, one of the NDRs has to be misleading. A way to check this is to do a paper LER test by printing a step tablet and measuring the LER range from 0.04 above Pb+f and 90% of the D-Max. Chances are the paper's LER will be closer to 1.05 than 1.20. As Chuck's curve clearly shows, at a relative 2.1 log-H range, the negative density range is 1.20. One stop down at VII or a relative 1.8 log-H range, the negative density range is 1.05 which would account for a one stop flare factor. In effect, the addition of flare means you are processing the film for a one stop less luminance range. Characteristic curves are great but they need to be interpreted. Please refer to my attachment in post #34 or the four quadrant reproduction curve in post #28.

If you actually process the negative for a 1.20 NDR and include flare into the equation, you get:

1.20 / 2.2 - .40 = .67 or
1.20 / 2.1 - .40 = .70

and from the Kodak example: 1.05 / 2.1 - .25 = .57

For speed determination, flare is built into the 0.10 over Fb+f when plotting the curve.

Steve

Chuck P.
24-Jan-2010, 14:18
The View Camera appears to have it for sale for about $60.


Thanks
Hmmm, that's about the price of box of 4X5 TMX, hmmm.....

Anyway, I did download the demo version and it looked pretty interesting and I like the idea of being able to use the fixed density point of 0.1 over b+f.

ic-racer
24-Jan-2010, 15:05
In testing hundreds of films over the years I have found very few cases where the ISO rating of the film was incorrect.

I'm in big agreement there. In fact I'll go so far as to say the best way to calibrate a sensitometer is with an appropriately processed fresh piece of name brand film. :)

Stephen Benskin
24-Jan-2010, 15:09
I have also downloaded a trail version of BTZS Plotter. I'm still not thrilled with it. I like my own program better. Still, the BZS plotter is better than doing it by hand, and it's just fine for anyone wanting better control.

Sandy, I thought there was a way to have a screen with both the film and paper quadrants.

sanking
24-Jan-2010, 16:22
Sandy, I thought there was a way to have a screen with both the film and paper quadrants.

Try New Matcher under the File menu.

Sandy

Stephen Benskin
24-Jan-2010, 16:40
Try New Matcher under the File menu.

Sandy

The Demo won't do New Matcher, but has a sample match file. The tabs available are "info", "Film", "Paper", and "Compare". The "Compare" tab only has Zone "boxes" showing the distribution of the tones. "Film" only has the film curve, and "Paper" only has the paper curve.

Bill Burk
24-Jan-2010, 19:43
Enlarger & Step Tablet testing sub-thread
Testing T-Max 400 in D-76 1:1

Took lens out of enlarger and put 80B filter (didn't have an 80A) over the opening in the 3-inch lens cone of Omega DII standard 4x5 condenser head with PH-212 bulb on a voltage regulator. I set an incident meter to ISO 64 time 4 seconds and raised the head until (now it is 25-inches above easel) incident meter indicated f/1.0

For cross-reference, Pentax spotmeter aimed at white paper on the easel barely clears 1 EV.

I set a mechanical repeating timer to 5 second exposure by watching the sweep hand of the Gralab. (I figured with a long time like 5 seconds a fractional second error would be tolerable). I made contact exposures of a 21-step Stouffer scale. Using CompnTemp timer target 68-degrees and 11x14 trays.

I got some densities but there are enough problems that I have to throw out the test. Problems of my own. On two sheets I saw images and Grafmatic frame numbers. I think that was "Doc" the horse. So my fresh film box really isn't fresh film. And I lost count of the chimes so I can't be sure whether I developed for 6 or 7 minutes. I know it was whole minutes but development time isn't supposed to be an uncontrolled variable in these tests.

The sheets that came out need more "headroom". Step 3 on the wedge only corresponds to Zone IX. I'd like to see X and XI maybe XII. My speed point hovered around step 17, so I have room to hit the film with more light.

I can bring the enlarger head down until it reads another stop brighter. (2 EV on Pentax aimed at white paper). And I can increase time to 10 seconds. But 1 second is the point where reciprocity failure starts to be a problem and I'm crossing that line.

So if I could have gotten the easel to EV 5 on the Pentax aimed at white paper, I think the exposure for TMax400 would have been 1 second to fit 10 stops on the 21-step strip. I don't think I can do that with the current setup. I'll pull out another enlarger next week and see if it can hit that illumination level.

Then I'll watch an auction site for a sensitometer.

Stephen Benskin
24-Jan-2010, 20:06
Bill,

Just a reminder not to forget about reciprocity failure in the tests.

The EG&G Mark VI or VII are popular sensitometers. I believe they were used by the military. When the military shifted to digital, they became readily available. Aerial photography uses them too. I have two. The first cost me around $1000 back in the early 90s. The second came from Ebay and cost a lot less.

Now, while they produce very consistent and repeatable exposures, you can't be certain what the illuminance is without it being calibrated. EG&G used to check the exposures, make sure the electronics were working properly, and include a new step tablet and these variable area filters which act like ND filters all for around $300. Later, they began to charge $1200 and I'm not sure if they still even offer the service. Uncalibrated only means you can't have actual log-H values.

Bill, I might be willing to part with my spare if you're interested. I also can make a copy of the copy of the instruction manual.

Steve

Stephen Benskin
25-Jan-2010, 00:48
I've attached a two quadrant film and paper curve demonstrating how the film curve fits the paper. The development indications for N-1, N, N+2, and N+2 are based on a fixed flare model which tends to overprocess as the development increases. The amount of information obtainable with sensitometry is well worth the learning curve.

Stephen Benskin
27-Jan-2010, 00:17
I've attached an example of how flare affects the shadow exposure and consequently film speed. It only covers the metered exposure point to the shadows. The values are in meter candle seconds and are generated using the camera exposure equation. Each step represents 1/3 of a stop. The exposure is for 125 speed film. For a 125 film speed, the exposure should be 0.0064mcs. Notice how that point is 1.0 or 3 1/3 stops below the metered exposure point for the non flare model. This can be thought of as the type of values you will get from exposing a contacted step tablet. The flare values shows that the 0.0064 is reached one stop further down or 1.3 log-H or 4 1/3 stops. The ISO point is 1.0 log-H units down from the metered exposure point because it is tested using a no flare approach.

Stephen Benskin
27-Jan-2010, 22:54
Here are two excepts from Phil Davis' book Beyond the Zone System which are pertinent to this discussion.

Page 94 Beyond the Zone System, fourth edition

“Because the fractional-gradient method of speed point location is difficult to implement in practice, it was important to find some simple calibration procedure. Finally, researchers concluded that when a realistic safety factor of about one stop is included in the fractional-gradient measurement procedure and when the film is developed to an average gradient value of about 0.7, the fixed-density and fractional-gradient are in close agreement. The current ANSI and ISO standards approximate this condition by specifying an exposure range of 1.3 and a density range of 0.8, with the sped point, or IDmin, located at the 0.1-over-B+F level. The average gradient of this standard curve is approximately 0.62.

It’s important to understand that the ISO speed point is only a point of reference from which the official film speed number is calculated.”

Page 95

“This final adjustment is necessary because your curve data are based on a no-flare test condition, but you’ll be applying the data to camera exposures that invariable involve significant amounts of flare.”

Rafal Lukawiecki
18-Sep-2012, 06:13
I have also downloaded a trail version of BTZS Plotter. I'm still not thrilled with it. I like my own program better. Still, the BZS plotter is better than doing it by hand, and it's just fine for anyone wanting better control.

Stephen, is your program/software for plotting characteristic curves available anywhere?

Stephen Benskin
19-Sep-2012, 20:03
Stephen, is your program/software for plotting characteristic curves available anywhere?

Sorry no. I'm a terrible programmer. I can barely manage get them to the point where they will work just well enough for my needs but they are light years away from being ready for consumers.