Adams/Archer Zone V Range

After more research and discussion here and elsewhere I have concluded that:

film: the characteristic curve maps logH (illuminance on the film to the resulting log10(Density) i.e. log10(1/(reflectance or transmittance))

digital: DPR's test curves map the 21 Stouffer steps to 8-bit sRGB.

Therefore both X-axes are logarithmic: the one base 10; the other base 2.

BUT the Kodak/Stouffer wedges have a much greater range 0.05-3.05 (10 EV) of density than film say 0.2-2.3 (7 EV) and none of them have 18% gray at the logarithmic mean. Furthermore, most Zone step diagrams don't have 18% gray in the middle, instead showing 127 or 128 out of 255! (everyone and his dog including CIPA/ISO knows that 18% gray maps to 118/255).

So the Kodak/Stouffer wedges just serve as a reference range for determining the characteristic curve for films - which do vary quite a lot.

And so-called "middle gray" is picked out of the air by various entities i.e. it is not always 18%.

Case in point: most Zone tutorials have Zone V at 127/255 i.e. close enough to 0.5 which, working backward to the sensor via 2.2 gamma, gives about 22% exposure, not 18%.

Recently found this Kodak illustration which maps density to both reflectance and 8-bit RGB (2.2 gamma, also 1.8 gamma)

Unlike other step-wedges this one has intervals of 0.1 density i.e. neither full nor half steps, but about 1/3 step.

Belated but I now agree with that.

There was always the belief that Kodak manipulated the standards so they could inflate the ISO ( and prior to that the ASA or DIN) rating of their B&W films. A big part of the ISO rating of B&W film was the developer and development protocol. Kodaks data was based on a specific developer, at a specific time and temperature and a specific agitation protocol. However, you sell more TriX when it is rated at 400 when the real working sensitivity was closer to 200. You sell more PanX when you sell it at 64 instead of the 32 which was closer to reality. One would like to say Ilford was more accurate, but alas they weren't - HP5 was in reality 200 not 400. Agfa was actually more realistic in their ratings based on my data Agfa B&W films were only about 1/2 stop inflated. In reality - film was a chemical based medium. The size of the grains and the shape of the grains went to determine the chemical properties associated with now many photons were required to case the reaction with the silver halide. Also ISO in B&W film is not absolute in that it is based on a set of assumptions on how the film is processed, chemicals, development procedure, etc. The data coming out of Kodak, Ilford and to a less extent Agfa were not really usable in the real world to get the best exposure. That was the reason Adams and Archer and to a lesser extent White developed and refined the Zone system calibration. To realize their vision in their prints - they had to know precisely how the film would react. Until one knows the development of a film, it is difficult to say much about ISO. On the other hand one needed a way to estimate the sensitivity of a film to light. Kodak at least told us exactly how they developed the film in estimating the sensitivity. They didn't really lie. However, many of the best photographers found their process to be biased to inflate the actually sensitivity of the film.

As far as I see with digital - it amounts to mostly smoke a mirrors. 🤪

Fully agreed, especially with the advent of REI which makes ISO anything Chuck Norris er, the manufacture says it is.

By coincidence, I am reading Conrad's informative paper on that and related stuff:

www.largeformatphotography.info/articles/conrad-meter-cal.pdf

In one sense, this whole discussion is largely not relevant to what Adams and the zone system was doing. @tprvevatt is getting close. Mathematical precision in defining a tone was not what was going on.
What mattered was the premise that the eye could distinguish just 10 shades of grey from pure black to pure white and the zone approach wanted total control to be able to get those shades where the photographer wanted them in the final print. The maths weren't relevant.
What is being missed here is the role of the Weston lightmeter. The rotating scale dial of the Weston enabled the calibrated grey scales to be assigned directly to the Weston. The photographer could use the calibrated Weston to read the exposure setting that would give the required tone on the print when the film/developing/printing process was carried out exactly to the calibrated process. The precision needed meant that a specific camera and lens, not the camera and lens models, had to be calibrated for a process where a particular film, developed with precisely the same developer temperature, dilution and agitation was then printed with a particular enlarger/condensor, paper and paper contrast and paper developer. We tend to forget that mechanical shutters were not very accurate or consistent between examples of the same model so calibration had to be done with the specific camera.
It didn't matter what the reading was that the grey assigned to a zone on the weston was. Two different photographers using identical gear might have different readings on their westons. What mattered was the ability to deliver required tone of grey, where wanted on the final print.
ie., the maths wasn't of much consequence. I think it used to be possible to buy grey scales that could be applied to a calibrated Weston's outer disk so the grey could be read directly as a tone rather than a number.
If we apply this to digital image making, the principal remains the same but of course consistent processing is no longer an issue, electronic shutter controls are far better and individual tones can be adjusted PP. Nik Silver Efex has a 10 tone scale available for those who want to use it in B&W processing. You would still need to do some testing and calibrating if complete accuracy is wanted when making prints.

Pentax spot meter I think, rather than the Weston. I know you could get them for both the analogue and the later digital. I made my own.

Since Adams did a lot of the work you could then just crib his notes as a starting point. Then you can have a streamlined system where you note the Zone 1, V and VIII and adjust your ASA nd development until they are where they should be. But it's single still values you work with rather than a range.

I used the Pentax one degree digital meter. Zone VI Systems modified these meters by adding additional baffling to mitigate reflections from outside the circle did not impact the light reading. They also added a strip on the barrel of the meter that was marked in zones so once your film and development was properly calibrated for the individual camera - then you could accurately predict the tonality of an image from the metered data to calculate the proper exposure for the film/development/camera. The individual camera played a role since the Zone System was developed long before shutter speed was electronically controlled. Shutter speeds would vary from camera to camera and since they were mechanical - they could change over time. I routinely would have my shutter calibrated to keep it close to specifications in my RB, M4 and 4x5 lenses. Yes the Zone systems was designed so one could accurately see in shades of gray by scanning a spot meter over the scene and adjust accordingly the exposure and development to get as close to the pre visualized image as possible with the remainder accomplished in the printing process.

The years must be catching up. Yes, you are correct, the Pentax spotmeter was the way to go and was the device used by Adams. I couldn't afford one of those so I used the Weston where grey tones could be assigned to the outer dial.