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Effective film speed (as in Lambrecht's method)
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A
- Thread starter Doc W
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Thanks Bill for that info.
Hey Bill, I believe you accidentally reversed the equation. LER / (LSLR - Flare) = aim CI
For Doremus. Personal choices and preferences are an important part of the process. It's an artform after all. The subject is called tone reproduction theory and it is based on sensitometric determination of the type of results obtained in practice. Let's not forget Jones' first excellent print test. It doesn't necessarily account for each photographer's personal taste but it gets you close enough so all the photographer needs to do is tweak. I don't know of any Zone System photographer that doesn't use the ISO rating as a jumping off point in their testing.
"many of us (especially those that use ZS metering techniques) end up finding that an E.I. different than box speed works better." I've written extensively on this point. The different results are mostly attributable to Zone System testing being a different methodology than ISO testing with the results being approximately the same as the ASA speeds obtained before the 1960 changes. Technically the results from Zone System testing produce a false sense of precision, but fortunately exposure doesn't have to be precise and giving 1/2 to 1 stop more exposure is just allowing for a higher safety factor, or personal taste. I believe I wrote in my last post that testing for speed for the individual was rather pointless because of the level of precision necessary to produce real meaningful results. ISO testing has already created a starting point in which to begin shooting and evaluation of the results based on the individual's personal approach.
The attached paper is how I determine processing.
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Here are copies of the spreadsheet and accompanying PDF of the relevant pages from WBM, as downloaded by me in 2013:
There is a minor bug in the spreadsheet:
On the "Input Data" sheet, you can (optionally) change the "Relative Dmin/Dmax" values in cells K49 and L49. If you do, you won't get the expected effect. This is because the difference between these two values (the wanted range) should be used in a few places, but isn't; instead, the constant 1.2 is.
On the "Curve <N>" pages, there are formulas in cells K49 and L49 to calculate "N", and they are, respectively, "=(2.1-(1.2/K48))/0.3" and "=(2.1-(1.2/L48))/0.3". Those "1.2" constants shouldn't be; they should be the calculated difference between the absolute Dmin/Dmax in K43 and K44, so, "=(2.1-(($K44-$K43)/K48))/0.3" and "=(2.1-(($K44-$K43)/L48))/0.3".
On the "Summary" page, the constant 1.2 is again used in cells P33 to P37. Here, the range end points aren't readily available on the page, so replace "1.2" with "($'Input Data'.$L$49-$'Input Data'.$K$49)"
I've changed this in my working copy, but not in the one linked to above; that one is as distributed by Ralph Lambrecht.
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RalphLambrecht
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he is but You were asking for an explanation in somebody else's words and that is legit. I aleady said all I can about the subject,
RalphLambrecht
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Stephen and Bill,
Thanks for the replies. As you know, I don't have the equipment or the desire to do the type of testing that you both do. My testing approach is based on that expounded in The New Zone System Manual by White, Zakia and Lorenz. It is a visual approach and highly empirical as well as individual, relying on "proper proofs" and visual inspection. I get well-exposed and developed negatives that work well for my purposes.
I used to do all the ZS film-speed testing, but found, as you point out, that the ISO rating minus 2/3-stop for my ZS metering practices, works well as a starting point. Many of the film I use I end up rating at 1/3-stop slower than ISO, not really much of a difference and possibly simply developer-related.
I also agree that the ZS can lead to a false sense of precision. IM-HO, the main advantage of the ZS is its use as a tool for visualization. At least I can try to hit the window as far as exposure and development are concerned, that lets me make the print I envisioned when releasing the shutter.
Flare, however, seems to me to be such a variable factor in the equation that pinning it down to a particular value can only be a rough approximation. Using a well-coated lens in ideal lighting conditions with a hood and top-quality enlarging lenses introduces much less flare into the system than slapdash use of an uncoated lens without a hood and in situations with the sun or other brighter areas (even bright overcast) just out of the image area, etc. How do you deal with the variability of flare in your calculations? Simply find an average value and then let the chips fall where they may, or?
Best,
Doremus
Thanks for the replies. As you know, I don't have the equipment or the desire to do the type of testing that you both do. My testing approach is based on that expounded in The New Zone System Manual by White, Zakia and Lorenz. It is a visual approach and highly empirical as well as individual, relying on "proper proofs" and visual inspection. I get well-exposed and developed negatives that work well for my purposes.
I used to do all the ZS film-speed testing, but found, as you point out, that the ISO rating minus 2/3-stop for my ZS metering practices, works well as a starting point. Many of the film I use I end up rating at 1/3-stop slower than ISO, not really much of a difference and possibly simply developer-related.
I also agree that the ZS can lead to a false sense of precision. IM-HO, the main advantage of the ZS is its use as a tool for visualization. At least I can try to hit the window as far as exposure and development are concerned, that lets me make the print I envisioned when releasing the shutter.
Flare, however, seems to me to be such a variable factor in the equation that pinning it down to a particular value can only be a rough approximation. Using a well-coated lens in ideal lighting conditions with a hood and top-quality enlarging lenses introduces much less flare into the system than slapdash use of an uncoated lens without a hood and in situations with the sun or other brighter areas (even bright overcast) just out of the image area, etc. How do you deal with the variability of flare in your calculations? Simply find an average value and then let the chips fall where they may, or?
Best,
Doremus
Maybe they should only use flareless cameras and flareless lenses.
Doremus, it's an average. Just like normal processing is based on the statistically average luminance range of 2.20. There's an average level of flare for a scene having a general distribution of tones. Flare is variable and most of it is caused by the subject. Two scenes with the same luminance range can have very different levels of flare is one is predominantly black with some white and the other is mostly white with a little black. Paper and printing techniques can be utilized and there is also the idea that flare is acceptable and even expected that in certain cases. You don't expect back lit scenes to look the same as front lit. The lower local contrast is expected and part of the look and mood.
Average flare with modern lenses is about 1 stop for a luminance range of 2.20. 35mm lenses with more lens elements generally have slightly higher levels of flare. Based on their aim CIs, Kodak has apparently been having a little debate over the average degree of flare. What is considered normal development begins with a scene with a 2.20 log luminance range. A CI 0.56 has about a stop of flare to just over a stop depending on rounding. CI 0.58 is about 1 1/3 stops of flare. Under Dick Dickerson, Kodak used CI 0.58 for normal. Before they used CI 0.56. In the last few years, it looks like it's back to CI 0.56. The difference doesn't really mean much in practice, and the saving grace to photography is that it doesn't really matter because you can do almost anything and still have a printable negative under average conditions the majority of the time; however, most of us here probably want something slightly better. So the idea is to aim for the bullseye in order to have the best chance of hitting the target. As with any model, how good it's considered to be is how well it works in the greatest number of circumstances. With an emphasis on greatest number of circumstances. For example, Jones found the fixed density method for determining speed isn't as precise across the board as the fractional gradient method; however, most people get by just fine using the fixed density method. The difference under average conditions, depending on film type, is negligible, but it becomes more obvious when the conditions become more extreme.
I put together something that is kind of interesting. I took the normal distribution curve of luminance ranges, and asked if a negative was processed to Normal (CI 0.58) under the different luminance ranges, where would it fall on the various paper grades. In other words, if I just went out and shot and processed everything normal, what grade would theoretically produce an acceptable print. One standard deviation includes 68% of all data points or more than half of all encounters. Below they would fall in the middle of Grade 1 to Grade 3, excluding personal taste. This suggests most personal testing methods don't have to be too accurate while still producing a usable negative in most cases.
Average flare with modern lenses is about 1 stop for a luminance range of 2.20. 35mm lenses with more lens elements generally have slightly higher levels of flare. Based on their aim CIs, Kodak has apparently been having a little debate over the average degree of flare. What is considered normal development begins with a scene with a 2.20 log luminance range. A CI 0.56 has about a stop of flare to just over a stop depending on rounding. CI 0.58 is about 1 1/3 stops of flare. Under Dick Dickerson, Kodak used CI 0.58 for normal. Before they used CI 0.56. In the last few years, it looks like it's back to CI 0.56. The difference doesn't really mean much in practice, and the saving grace to photography is that it doesn't really matter because you can do almost anything and still have a printable negative under average conditions the majority of the time; however, most of us here probably want something slightly better. So the idea is to aim for the bullseye in order to have the best chance of hitting the target. As with any model, how good it's considered to be is how well it works in the greatest number of circumstances. With an emphasis on greatest number of circumstances. For example, Jones found the fixed density method for determining speed isn't as precise across the board as the fractional gradient method; however, most people get by just fine using the fixed density method. The difference under average conditions, depending on film type, is negligible, but it becomes more obvious when the conditions become more extreme.
I put together something that is kind of interesting. I took the normal distribution curve of luminance ranges, and asked if a negative was processed to Normal (CI 0.58) under the different luminance ranges, where would it fall on the various paper grades. In other words, if I just went out and shot and processed everything normal, what grade would theoretically produce an acceptable print. One standard deviation includes 68% of all data points or more than half of all encounters. Below they would fall in the middle of Grade 1 to Grade 3, excluding personal taste. This suggests most personal testing methods don't have to be too accurate while still producing a usable negative in most cases.
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Bill Burk
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Maybe it feels that way but you know, as a teacher, students always need to hear it again.
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- Chuck_P
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Yes it would. Good catch.
Thanks so much for your detailed response, Stephen. I'll keep aiming for that bull's eye and hoping I hit the target most of the time 
I'm doin' pretty well most of the time.
Doremus
I'm doin' pretty well most of the time. Doremus
Stephen, does this apply equally to an aim gamma? Thanks.
As Normal for gamma is in the low 0.70s and normal for CI is in the high 0.50s, it probably wouldn't be a good fit. Gamma wouldn't be my first choice as it only applies to the straight-line portion. Almost any average gradient method would be more applicable.
Thank you
RalphLambrecht
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