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Tim Meisburger
17-Jan-2010, 21:30
I was recently reading a description of the process for determining personal exposure index for various film. It seemed complicated, and I wondered why I could not merely do this:

- meter zone five on a zone card and set the appropriate exposure using the film's standard ASA
- photograph the zone card
- process normally

Then, if zone five was the center of the spectrum, you would assume your PEI matched the film rating. If zone five was shifted one or two stops in either direction, you would re-rate the film accordingly.

I don't know much about this sort of thing, so I'm sure its not that simple, but I cannot figure out why...

pocketfulladoubles
18-Jan-2010, 14:00
Sounds reasonable, but like you, I'm a novice. I'm not sure what type of film you are using, but what I've found in my unscientific try-it-and-let's-see approach is that you don't necessarily get the same # of zones above and below 5. For that reason, I sometimes bias my exposure down so as not to overexpose the brighter parts and lose color.

ic-racer
18-Jan-2010, 14:54
If PEI means Personal Exposure Index, then it is simple.

Photograph a uniform target with an exposure that places it at zone I using a guess at exposure index.

Process the film. If the density on the film is 0.1 d ( 1/3 of a stop ) then your guess was correct. You can use a densitometer or place the film over you exposure meter and look for a 1/3 stop drop of the needle. (If you have a densitometer, look for a density of 0.1 log d).

Bruce Watson
18-Jan-2010, 15:07
I was recently reading a description of the process for determining personal exposure index for various film. It seemed complicated, and I wondered why I could not merely do this:

- meter zone five on a zone card and set the appropriate exposure using the film's standard ASA
- photograph the zone card
- process normally

Then, if zone five was the center of the spectrum, you would assume your PEI matched the film rating. If zone five was shifted one or two stops in either direction, you would re-rate the film accordingly.

I don't know much about this sort of thing, so I'm sure its not that simple, but I cannot figure out why...

Because finding your personal EI is about shadow detail, not midrange detail. Midrange will vary (a lot) more with development (time, temp, agitation, etc.), so midrange is not a good indicator of EI.

To find out more I recommend finding a copy of Fred Picker's Zone VI Workshop (http://www.alibris.com/search/books/qwork/7394269/used/Zone%20VI%20Workshop:%20The%20Fine%20Print%20in%20Black%20and%20White%20Photography). Mr. Picker explains Zone System testing in very easy to understand terms. Nice and simple, yet complete.

ki6mf
18-Jan-2010, 15:52
This was from an earlier post from Gem Singer

Re: Multi-spot metering in b&w landscape from Gem Singer 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.

A good tutorial on line that will step you through exposure and film speed is located at
Film Speed Test and Developing Test from Jerry Orabona Photography http://www.jerryo.com/teaching.htm

Lachlan 717
18-Jan-2010, 16:22
This was from an earlier post from Gem Singer

Re: Multi-spot metering in b&w landscape from Gem Singer 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.



I'm not sure this is what is being discussed here...

Tim Meisburger
18-Jan-2010, 17:17
ic-racer (what does that mean anyway?) - That looks like an interesting way to measure density, but if I guess wrong, do I still need to make more test prints to determine the EI, or is their a scale or table that will tell me how far off I am based on a meter reading (I don't have a densitometer).

Bruce - I don't really understand, To hold detail in zone 3, you need to be able to differentiate areas that are zone two and one in the shadow area. If I can differentiate these zones on a photo of a chart, wouldn't that mean I could see detail in shadow in a regular negative?

Wally - That's a pretty succinct summary of the zone system, but Lachlan is correct in that what I am really asking is about film testing. I had a look at the link you posted, and the method described is the normal one where up to ten separate exposures are made. In the third method described he seems to be looking for a neutral gray, which is the same reference I would be using looking at one shot of a zone chart.

ic-racer
19-Jan-2010, 11:39
ic-racer (what does that mean anyway?) - That looks like an interesting way to measure density, but if I guess wrong, do I still need to make more test prints to determine the EI, or is their a scale or table that will tell me how far off I am based on a meter reading (I don't have a densitometer).

Radio controlled internal combustion racing. But also just way to maintain anonymity.

Yes, repeat the test with multiple exposure index guesses and find the one that gives you 0.1 density. That is basically the "Zone I" test. You can search for other variations on doing the test.

percepts
19-Jan-2010, 14:22
Tim there are many anomalies in the zone system. Forget about zone 5 and throw your 18% grey card away. It causes more confusion than just about anything else.
What you want is enough exposure to give you some shadow detail which is adjusted through setting personal EI and enough development to retain highlights detail.

So just follow the advice given above.

read the following thread which explains why your grey card is useless amongst other things.

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

percepts
19-Jan-2010, 14:52
I was recently reading a description of the process for determining personal exposure index for various film. It seemed complicated, and I wondered why I could not merely do this:

- meter zone five on a zone card and set the appropriate exposure using the film's standard ASA
- photograph the zone card
- process normally

Then, if zone five was the center of the spectrum, you would assume your PEI matched the film rating. If zone five was shifted one or two stops in either direction, you would re-rate the film accordingly.

I don't know much about this sort of thing, so I'm sure its not that simple, but I cannot figure out why...

doesn't matter what kind of card you point your light meter at. The result will be the same which is an exposure which will make the result middle grey.
Problem is you think a "Zone Card" is a true middle grey but they never are. I assume you are thinking of a kodak 18% grey card. Well 18% is not the middle of a 10 zone system and your light meter is not calibrated to 18% even if 18% was the middle of a 10 zone system where each zone is 1 stop.

Tim Meisburger
19-Jan-2010, 17:13
I think I may have described this poorly, and confused the issue by mentioning the zone system. I am not really interested in exposure, I am suggesting that a chart with 11 tones or shades ranging from black to white, each a stop apart, would be a better test target for testing film than would the "average" scene generally recommended. It happens that such charts are used to illustrate the zone system (here is an example: http://www.cabbagetownphoto.com/zone.html). Using a step chart would, in one exposure, tell you whether your rated film speed is correct (the middle tone on the chart would be the middle tone in the negative), or provide a quantitative indication of how many stops you need to shift your exposure from the rated film speed.

For example, if on your negative the middle tone was zone VII of the test target, you would know you needed to reduce film speed two stops to ensure zone V in the negative matched the Zone V in the test target (actually, if comparing the negative to the positive chart this would indicate a two stop increase, but you get what I mean). No need to shoot a lot of film at different stops.

Also, this test would tell you how many zones your film could cover, and would simplify determining normal, +1 and -1 development times.

I believe that printers (humans not machines) use step charts or wedges for test and wonder why photographers do not.

percepts
19-Jan-2010, 17:36
Because if you put any chart in bright sunlight and measure the difference between the black patch and the white patch, it won't be 10 stops. You'll probably only get 5 to 7 stops at most. So you have to manufacture a lighting source to do it and some people have. But why bother when you can just expose a zone 1 neg and a zone 9 neg and print them with same time to find if everything is OK.

If you meter a shadow subject and then meter a bright cloud the two parts of the scene are in different lighting so you can get a brighter range than 10 stops. But with your zone chart you would have to manufacture lighting exactly for the dark and the light areas to be sure you had a exactly a 10 stop range. So you'd need flash and a lot of messing about to do it. Why make things difficult.

Lachlan 717
19-Jan-2010, 18:01
I think I may have described this poorly, and confused the issue by mentioning the zone system. I am not really interested in exposure, I am suggesting that a chart with 11 tones or shades ranging from black to white, each a stop apart, would be a better test target for testing film than would the "average" scene generally recommended. It happens that such charts are used to illustrate the zone system (here is an example: http://www.cabbagetownphoto.com/zone.html). Using a step chart would, in one exposure, tell you whether your rated film speed is correct (the middle tone on the chart would be the middle tone in the negative), or provide a quantitative indication of how many stops you need to shift your exposure from the rated film speed.

For example, if on your negative the middle tone was zone VII of the test target, you would know you needed to reduce film speed two stops to ensure zone V in the negative matched the Zone V in the test target (actually, if comparing the negative to the positive chart this would indicate a two stop increase, but you get what I mean). No need to shoot a lot of film at different stops.

Also, this test would tell you how many zones your film could cover, and would simplify determining normal, +1 and -1 development times.

I believe that printers (humans not machines) use step charts or wedges for test and wonder why photographers do not.

Tim,

Have a look at http://www.stouffer.net/TransPage.htm.

These are "see thru" step wedges that allow you to compare your film test results to a defined one.

They might help.

The issue that you have (as I see it) is that the toe of the exposure curve varies from film to film, as it does from process times/strengths etc within the same film. What you are trying to find out is where that particular "event/curve" occurs. Going for mid grey/18% grey/zone V only tells you what is happening on a straight part of the curve.

You need to know the lowest usable zone so that you can work up (understanding that a true mid grey can be manipulated to most other zones in printing, but you can never get detail into black shadows). Similarly, you also need to know the top end of the zone so that you can process to expand/contact the highlights.

If you want to get a reasonable/simple/quick EI test, here is my suggestion:

Do you have access to a roll film camera (pref. 120 film), light table and a spot meter? I would suggest doing some tests using a roll of film, starting from your base+fog "blank" shot, running at 1/3 or even 1/2 stop increases, from indicated Zone 0 (or even Zone -1/2 if film permits) until the roll is done (recording each frame's exposure details). Once you have processed this roll in a controlled fashion, use your spot meter to find the frame that is 1 stop brighter than the unexposed frame (make sure that you mask each frame so that only light passing through the frame is visible).

Then work out how many stops (or parts thereof) worth of frames there are between these 2 frames, compare this to your starting exposure value (eg. Zone 0) and you should have your compensation factor for the specific film/process you used.

This might not be as accurate as the techniques in some books (and no doubt some Forum Members' techniques), but it is close enough to get you started!

Tim Meisburger
19-Jan-2010, 18:32
Yes Lachlan. I have been looking at the Stouffer site, and have ordered one of their zone system charts. The way they use step charts to set exposure for printing in the graphic arts is the model I am suggesting, but I have not seen anywhere on their site or elsewhere a description of using this technique in normal (as opposed to copy) photography.

percepts
19-Jan-2010, 18:40
film curves are not usually straight from 0 to X so your theory goes right out the window.
Some films have a low zone V and some higher. How are you going to handle that one?

Tim Meisburger
19-Jan-2010, 18:57
Okay. I think I have it figured out now. I searched "step wedge" instead of zone chart and got some information on using these to test film and paper. Typically, they use a transparent 4x5 step wedge calibrated in half stops instead of full stops (like a zone chart) and either contact print it on paper or insert it over the negative in a 4x5 holder and photograph a blank wall. This is essentially the same process as photographing the chart itself. This is apparently explained in the book BTZS with analysis done based on densitometer readings, but it seems to me that if you can test film by visually evaluating a standard scene, then you could do the same visually evaluating a step wedge.

Anyway, I printed out a zone system chart and will give this a try.

Chuck P.
19-Jan-2010, 19:03
doesn't matter what kind of card you point your light meter at. The result will be the same which is an exposure which will make the result middle grey.
Problem is you think a "Zone Card" is a true middle grey but they never are. I assume you are thinking of a kodak 18% grey card. Well 18% is not the middle of a 10 zone system and your light meter is not calibrated to 18% even if 18% was the middle of a 10 zone system where each zone is 1 stop.

It would be the middle of an 11 step zone scale from zone 0 to zone X. Zone 0 is full black and Zone X is paper white, Zone V then becomes the geometric midpoint between full black and paper white. With the geometric midpoint at V, there are four distinct steps of gray on each side of it. So, an 18% gray card in ZS terms is the geometric midpoint of the zone scale.

Lachlan 717
19-Jan-2010, 19:04
film curves are not usually straight from 0 to X so your theory goes right out the window.
Some films have a low zone V and some higher. How are you going to handle that one?

Percepts,

Can you please explain what you're writing about? Whose theory? Perhaps quote the part that you're referring to...

Chuck P.
19-Jan-2010, 19:16
But why bother when you can just expose a zone 1 neg and a zone 9 neg and print them with same time to find if everything is OK.

This is fine, but the enlarging exposure time is critical if your're to evaluate the efficiency of your Zone I and IX exposures, it must be based on a time used to print a middle gray value. To do that, a Zone V exposure is made, then printed so that its print value is matches the gray card. Use that enlarging time to print Zone I and the Zone IX negatives. This method is best if the target is a textured target, such as screen tightly secured to a uniform toned card.

percepts
19-Jan-2010, 19:22
This is fine, but the enlarging exposure time is critical if your're to evaluate the efficiency of your Zone I and IX exposures, it must be based on a time used to print a middle gray value. To do that, a Zone V exposure is made, then printed so that its print value is matches the gray card. Use that enlarging time to print Zone I and the Zone IX negatives. This method is best if the target is a textured target, such as screen tightly secured to a uniform toned card.

No it does NOT have to be based on a zone V exposure. You print zone 1 test strip to a give a tone just perceptibly lighter than max black and then use that time to print your zone IX neg to give a tone just perceptibly darker than paper base.
If the zone IX print tone isn't correct, then adjust adjust development. This of course assumes you want 10 zone system and not 8 or 9 or 7 or something else.

Doing it the way you suggest is saying a zone V must be 0.7 print density which takes a very lteral view of AA writings. But it doesn't take any account of the fact that film curves are not straight and that for most films you can never achieve what you are suggesting and get a full range of tones from 0 thru X. i.e. Zone V print density is not fixed in law.

Chuck P.
19-Jan-2010, 23:35
Zone V print density is not fixed in law.

Sorry for the long post, but....

No one is suggesting that it is as I can see it anyway. The graph showing two curves clearly indicates different "toe" densities to no detriment to the ability to achieve a full tonal range in the longer toe versus the very short toe film-----they were produced using standard ZS testing principles. And I've enjoyed good results from them. But they have obvious different "toe" responses to exposure and development as you can see. A long toe versus a short toe is only a different rendering of the low values in terms of contrast (shadows in a longer toed film will exhibit somewhat less contrast , but achieving a full scale is not affected as long as one has determined the personal EI by testing.

Both curves originate from the speed point (0.1 neg density at zone I) and cross the 1.3 "normal" development calibration line at Zone VIII, for my desired density range of 1.3 - 0.1 = 1.2. I was fortunate to get full box speed with D-76 1:1, no adjustment was needed. But I had to adjust the HC-110 curve and so provided the uncorrected curve to show how I did it. It's the same curve shape but it's a bit more stretched out on the page (due to the vertical axis going up to 2.5) than what is seen in the comparison curves (vertical axis goes to 2.0) .

The second graph showing the uncorrected curve shows that if I use the ISO of 100 with TMX and HC-110 (1:63), then I'm cheating the log exposure scale in the shadows by almost a full zone of print tonality. By correcting the curve for the desired speed point through a reduction of 2/3 off the box speed to EI64, I regain useful exposure between Zone I an II (easily seen in the comparison curve graph), thus maintaining complete scale in the shadows.

At the highlight end of the uncorrected curve, notice that the curve crosses the 1.3 density line at about Zone VIII 2/3 with an 11 minute development time. It was luck that after correcting for the speed point, the curve crossed the 1.3 line exactly at Zone VIII----easily giving me my "normal" development time of 11 minutes with TMX at an EI of 64. So, with one sheet of film I got the personal EI and "normal" development time, sometimes it works out that way. Usually, I would have to expose anther sheet to the step wedge at my new EI, then adjust the development time from the speed test to get the curve to cross the 1.3 line at Zone VIII, the lightest print tone that still shows some texture detail.

Anyway, your're suggesting that the curve shape (the liniarity or curvature of the toe) has something to do with being able to achieve a full scale of zones. I guess I would have to just disagree, and I doubt that I have proven anything to you. If one does not adjust the EI to get optimum log exposure, then he certainly would cheat himself of achieving a full scale in the shadows and if he does not calibrate "normal" development for optimum contrast in the highlights, he'll cheat himself there too. So, developing to a contrast range appropriate to the exposure scale of the paper will get a full scale print, that's my experience anyway, regardless of a longer toe or not. What matters, IMO, is taking full advantage of the available log expoure down to a useful lower density limit (0.1 above fb+f at Zone I), and then knowing at what upper density limit will print with contrast (Zone IX for very light tone, which should easily print Zone VIII for decent highlight texture) on the paper your're using.

Chuck

percepts
20-Jan-2010, 00:02
Your graphs illustrate perfectly what I said.

TMX in D76 giving neg density of 0.77 for zone V
TMX in HC110 giving neg density of 0.6 for zone V

They both have neg density of 0.1 for zone 1. But they would require different times to print the zone V at 0.7 print density because they have different zone V neg densities. But since they both have the same zone 1 density, printing them at different times would give you different zone 1 print densities which as you know, won't be right.

i.e printing zone 1 neg for print density and zone 9 for print density works. Printing zone V won't. Both ways will get you the range within your parameters but that wasn't the point. The point was that trying to use zone V as a print density check will lead you up the garden path to nowhere. Or as I said before, zone V is not fixed on print density 0.7 because if you try that you will not get zone 1 where it should be and correcting it by increasing print contrast will lose your shadow separation.

Lachlan 717
20-Jan-2010, 00:25
Tim,

Will you be printing or scanning?

Was your initial post only about setting your PEI?

Tim Meisburger
20-Jan-2010, 01:49
Hi Lachlan. It was only about determining EI and normal development, and I now think I have found a useful methodology here: www.paulwainwrightphotography.com/biblio_files/use_your_eyes.pdf. He uses a transmission step wedge sandwiched over a negative, but it is essentially the same as shooting a reflective step or zone chart.

I am only interested in printing, not scanners, as I spend too much time at the computer already. Thanks to all for the help.

Best, Tim

Chuck P.
20-Jan-2010, 06:23
They both have neg density of 0.1 for zone 1. But they would require different times to print the zone V at 0.7 print density because they have different zone V neg densities.

Your're confusing "tone" with "contrast", IMO. The D-76 curve will have a higher local contrast than the HC-110 curve at Zone V but it's tone value if printing a gray scale would be the same.

percepts
20-Jan-2010, 09:16
Your're confusing "tone" with "contrast", IMO. The D-76 curve will have a higher local contrast than the HC-110 curve at Zone V but it's tone value if printing a gray scale would be the same.

Let me assure you I am not confused. You stated:


This is fine, but the enlarging exposure time is critical if your're to evaluate the efficiency of your Zone I and IX exposures, it must be based on a time used to print a middle gray value. To do that, a Zone V exposure is made, then printed so that its print value is matches the gray card. Use that enlarging time to print Zone I and the Zone IX negatives. This method is best if the target is a textured target, such as screen tightly secured to a uniform toned card.

from your charts if you take the d76 curve and print the zone V to give an 18% middle grey (0.7 print density) and use the zone 1 and 9 negs to print using the same time and they print as they should. i.e. just perceptibly lighter than max black and just perceptibly darker than zone X.
Then if you do the same with the hc110 zone V neg you will require a shorter print time and if you apply that shorter time to your zone 1 and zone 9 negs then you will get a zone 1 print value which is too light and a zone 9 print value which is too light. You have completely avoided explaining that.
I think you need to print some zone negs to verify that your zone negs actually print how you think they're supposed to because I can see from your charts that they won't both work as you seem to think they do. This is because you mistakenly beleive that zone V will always print as 18% middle grey. This is only true for a curve of one specific shape. It is not true for other curves of which there are many. i.e. Zone V print value is not a constant. So your assertion that zone V must be prinetd as print value 0.7 density (18% middle grey) is wrong or you accept that zone zone 1 and zone 9 don't print where they are supposed to.
Once again AA has misled one of his disciples. This is one of the anomalies of the zone system which confuse his disciples when they are confronted with it because they refuse to beleive that he published something which is not right.

Ken Lee
20-Jan-2010, 11:44
As Bruce pointed out, Fred Picker's Zone VI Workshop (http://www.amazon.com/exec/obidos/tg/detail/-/0817405747/qid=1075561755/sr=1-2/ref=sr_1_2/002-7002570-7186453?v=glance&s=books) is very good.

Another fine book is The Negative (http://www.amazon.com/Negative-Ansel-Adams-Photography-Book/dp/0821221868/ref=pd_sim_b_3) by Ansel Adams.

Once you grasp the basics of development and exposure you might want to try the method recommended here (http://www.kenleegallery.com/html/tech/testing.html).

Chuck P.
20-Jan-2010, 18:19
I think you need to print some zone negs to verify that your zone negs actually print how you think they're supposed to because I can see from your charts that they won't both work as you seem to think they do.

My previous post said that the tones would be the same, but they will actually vary slightly because of the curve shapes in the toe region that we are discussing and will even affect the upper zones. What will be consistent, at least after I performed this, is the tone of the Zone V negative. I'll try to explain.

After restating my thought from this morning, understand that I would not have said what I said if I had not already done this, years back, but you believe what you want. I know for a fact that a representative gray scale can be produced off of both those curves in the manner that I have suggested, I've done it. Others can try it but the adjustment for personal EI and calibrating "normal" development should be accurately done, if not you probably won't be pleased with the results, IMO. What will be consistent is the tone of the Zone V negative as it is based off matching it to the gray card in the ZS way of performing the gray scale------ even though the density is 0.75 for my d-76 curve or 0.6 for my hc-110 curve (yes, the exposure time on the paper will slightly vary, as it should). This will vary slightly the actual tone of the remaining respective zones while maintaining an accurate zone description.

Why? Because the tonal value associated with each zone is actually the mid-point shade of gray for that zone; there are slightly lighter and darker shades of gray on each side of the zones, other than the 0 and X of course. There is wiggle room for the actual tone that represents any single zone of the gray scale that can be printed with contrast, this can be clearly seen in a short toed film versus a longer toed film in zones I-III or IV. The exception being there is really no wiggle room for Zone V. In the ZS way of doing things (yes, I know it is not the only way, yes, I'm sure it has flaws, but not that I can see in the way that you are putting forth), printing Zone V to match the gray card fixes the entire tonal scale and any variation in curve shape does not adversely affect the validity of the gray scale produced.

I've tried not to take the tone that you have chosen, it's not worth it, I'll just end the discussion and you can believe what you wish about it without further input from me. Not meaning to sound preachy here, I'm just describing my results after having performed these things myself. I'm glad we have one thing in common though, we both love B&W photography, we can at least agree on that. It certainly is a passion isn't it? :)

Stephen Benskin
22-Jan-2010, 04:43
This is one of the anomalies of the zone system which confuse his disciples when they are confronted with it because they refuse to beleive that he published something which is not right.

If you want to nit-pick, you can almost find a mistake on every page of the negative. My suggestion is for people to read a book on photographic sensitometry. Adams is mistaken about film speed, what the meter reads, and the aim density range of the negative, among others. The Zone System is best when used for visualization. Adams says that it is a simple form of sensitometry. Why not go to a more authoritative sources for that part?

Percepts is absolutely right. The negative needs to fit the paper; therefore, you need to know what the log exposure range of the paper is before determining the negative density range. Otherwise, the NDR is arbitrary. Condenser enlargers will require a shorter NDR for the same paper than a diffusion enlarger. Printing on platinum paper requires a very different NDR. Even Adams had different ZIII densities for diffusion and condenser enlargers.

Interesting enough, the 1.20 negative density range probably isn't what you are actually getting in the field. Yes, it works, but not for the reasons Adams claims. The curves Chuck P plotted look like they are from contacting which has no flare (ZS in camera testing has minimum flare). The average scene (7 1/3 stops BTW) has approximately 1 1/3 stops flare. That will reduce the negative density range of the film. If anyone is familiar with the ISO LERs for paper, they should remember that a grade 2 paper has as it's midpoint a LER of 1.05. Why the discrepancy? One takes into account flare. The other doesn't. Instead of reading the negative density at VIII, we should be looking at the negative density at VII because we lose around a stop of apparent subject luminance range - 2.1 - .3 = 1.8. The negative density at VII in Chuck's graph is 1.05.

Finding the average gradient of the curve is the best way to determine your aim development. To determine the aim gradient you can use a simple equation - negative density range (as determined by the paper LER) divided by the subject luminance range minus flare.

ISO 1.05 / 2.2 - .40 = .58
ZS 1.20 / 2.1 - 0 = .57

They are effectively the same which means that for a given scene they will produce the same negative density range. So, how can they have different aim negative density ranges? Adams never explains how film and paper relate. He doesn't even match the same Zonal ranges between negative and paper. He has the scene Zones from I to VIII which is seven stops, but has ten Zones for the paper. My belief is that he based the print Zones on the Munsell scale which has ten steps and 18% at step 5 (and it predates the ZS by 40 years). Another big anomalies is with ZS speed testing, but that is a story for another time.

The shape of the curve of the film and paper also determine where the Zone Values fall. Except for a single tonal placement, it is not possible to be certain where anything will fall. And that is if Zones had a predetermined value which they don't. Again, a study of sensitometry would help clarify it all.

Steve

Chuck P.
22-Jan-2010, 17:30
The negative needs to fit the paper

I couldn't agree more. My negative fits my paper very well, I know because I print with it and I have two fine looking gray scales one for each curve and my negative density range is pretty dam consistent with regard to the density of a shadow placement or where a highlight falls on the curve, perfect no, but very much controlled and workable by me, yes. You can argue with Adams all you want to as I believe your ego craves that friction, but you can't convince me against my own results that I see with my own eyes, although you always try to :D. But you and I have sort of had these discussions before :). I don't argue with what I have proven works for me, there's no need to when results speak for themselves, regardless of any real or perceived flaws in the system-----an excercise in futility if there ever was one.

Actually, the Zone VII density is 1.1 for d-76 curve and 1.02 for hc-110 curve, owing to the different curve shape of TMX with those developers and dilutions. Both produce a very nice Zone VII print tonality, albeit slightly different from each other, but more importantly, falling in line very nicely in tone progression on their respective scales relative to the curve from which they were produced. Now I just have no earthly reason to argue with that, but I appreciate your zeal anyway.

CP





Chuck

Stephen Benskin
22-Jan-2010, 18:01
You can argue with Adams all you want to as I believe your ego craves that friction, but you can't convince me against my own results that I see with my own eyes, although you always try to :D.
Chuck

Sorry that you think so. For me, it's a search for truth. I'm just saying things might work differently than the way people think. By understanding how things really work gives the photographer better control over the process. Adams spent very little ink dealing with sensitometry whereas there are whole book written on that subject. As the ZS is simplified sensitometry and tone reproduction, it's not unreasonable to address the accuracy of the system from a sensitometric standpoint.

In regards to the OP, one of the problems with ZS testing compared to the ISO film speed is that the ZS has Zone I four stops down from the metered exposure and the ISO film speed is 3 1/3 stops down. That's why ZS photographers have a disproportionately consistent results for film speeds that are around 2/3 of a stop below the ISO speed. Once again, the difference between the two points is one factors in flare and one doesn't.

In general, general developers will produce film speeds close to the ISO speed. The biggest reason to adjust the EI is to compensate for personal metering preferences or to add a little safety factor. My advice is to shoot a few rolls at the ISO speed, making sure the processing is correct, and decided if you like the way the negatives look.

Steve

Stephen Benskin
27-Jan-2010, 14:52
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.

The 1.0 log-H (3 1/3 stops) difference between the metered exposure point and the film speed point for black and white film is a fixed relationship. When doing ZS testing, stopping down 1.2 log-H units (4 stops) would be fine if there were ample flare withing the testing situation; however, a single toned card filling the frame produces minimal flare. Therefore, the ZS test will be more modeled like the no flare example. Stopping down four stops places the test point under the 0.10 aim density, which means the EI needs to be adjusted to bring the exposure back up. This is why the ZS produces almost universally lower EIs than the ISO speeds.