New web page about the Zone System

[Drew Wiley]

Stephen - I'm unaware of any film meter I've ever used that even sees in neutral gray. I do own a very expensive lab instrument that does. Many of our popular
meters, like the Pentax spotmeter, were designed with color cinema sets in mind. In this case the peak sensitivity is close to that of the human eye, atop the green
part of the spectrum. But different receptors, esp in the past, had their own spectral sensitivities. After awhile, people just get used to the idiosyncrasies of their
meters, I guess. And for those who use gray cards, well... I've found those to be all over the place in terms of alleged quality control, everywhere from 11% to
25%. Might as well be reading the back of your hand, like old timers did!

[Stephen Benskin]

12% Reflectance, not 18% Reflectance. Please refer to the defining K compliation.

[Drew Wiley]

Reflectance per WHAT, Stephen? With a spectrophotometer, there's typically an unfading calibration tile (or generally two). In nature, one only approximates gray as best one can. I'm accustomed to reading conifers and various shades of grass. Up in the mountains you've got various shades of diorite and granite etc. One bends meter technique to what one has, just like one bends the Zone System in any manner it works for him personally. I learned it, so now I can ignore it. Real sensitometery needs to be done under controlled circumstances. I shoot in uncontrolled circumstances, with the light often changing every few seconds. Don't have time for calculators or any kind of nonsense. The film curve and its development are all in the back of my head somewhere. It either fits or it doesn't. The most I ever want to worry about, besides the basic exposure itself, is segregating odd sheets of film for a slightly different development regimen.
After all, that's all the Zone System boils down to, once you master it. No sense making a religion out of it. It's about practical photography, not R&D.

[Stephen Benskin]

Reflectance per WHAT, Stephen? With a spectrophotometer, there's typically an unfading calibration tile (or generally two). In nature, one only approximates gray as best one can. I'm accustomed to reading conifers and various shades of grass. Up in the mountains you've got various shades of diorite and granite etc. One bends meter technique to what one has, just like one bends the Zone System in any manner it works for him personally. I learned it, so now I can ignore it. Real sensitometry needs to be done under controlled circumstances. I shoot in uncontrolled circumstances, with the light often changing every few seconds. Don't have time for calculators or any kind of nonsense. The film curve and its development are all in the back of my head somewhere. It either fits or it doesn't. The most I ever want to worry about, besides the basic exposure itself, is segregating odd sheets of film for a slightly different development regimen.
After all, that's all the Zone System boils down to, once you master it. No sense making a religion out of it. It's about practical photography, not R&D.

What I am talking about is theory (Exposure and Tone Reproduction). The math is there to explain it. Just like the Zone System (simplified Tone Reproduction Theory), understanding how the process works makes it easier to use. If you take the time to read my Defining K, you might begin to understand. Exposure meters want to place 8 lx on the film plane. Incorporate the film speed and you get 1/ISO * 8. The constant 8 can be referred to as P. So for a 125 speed film, 8/125 = 0.064 lxs is the midtone exposure. B&W speed point is Δ1.0 log-H units below the mid-tone exposure point. The speed equation is 0.8/H_m. H_m for a 125 speed film would be 0.8/125 = .0064. The following table shows the exposure breakdown for a 7 2/3 stop luminance range (the average is 7 1/3, but I add 1/3 of a stop to help illustrate flare). The RD that produces the 0.064 lxs film plane exposure is 0.92. Anti-log of that is 0.12 or 12%.



And the 297 cd/ft² is derived from the exposure meter standard when K = 1.16 cd/ft² or as your exposure meter might list it as 12.5 cd/m².

BTW, one of the papers in the link, An Interpretation of Current Exposure Meter Technology has a large section on photo cell spectral sensitivity and color temperature. Here's a graph from the paper you might find interesting.



All I'm doing is correcting some mistakes by the OP. He says meters see 18% reflectance. They don't. He claims a Gamma of 1.0 is normal. It isn't. I simply supplied the information supporting my position.

[Stephen Benskin]

Panoral, below is an example of a four quadrant reproduction curve. Notice how the original luminance range of 2.20 is reduce within the camera, by flare, The film is processed so that the resulting film density range matches the paper log exposure range. To print the average scene on a grade two paper, the gradient for this example is 0.56. The resulting tone reproduction gradient averages around 1.0. This curve is derived from comparing the original subject to the print.

[ALVANDI Camera]

Thanks to all. It was very useful information.