I interpret the same Zone VIII density. But I used the Contrast Index meter overlay to read CI from my hand-drawn chart where I transcribed the numbers. I see Ansel Adams didn't subtract Base plus Fog from the graphs, and when I came up with the lower CI, I had set the Contrast Index meter overlay on baseline zero. When I lift the CI meter to about 0.05 density (which is where I believe his Normal curve would zero out), I get close to 0.57 CI like you do.
I agree, Delta-X criterion justifies holding the same speed rating (so I will not include this specific 1/6 stop adjustment in my own personal EI), but most Zone System EI are taken from the 0.1 density mark, and that would definitely move for people reading Zone System tests.
The reason for working out factors of 1/6 stop is not to achieve a false sense of precision... I would round to the nearest 1/3 stop. For now, for me, that is 2/3 stop.
I just wanted to remind you that because of Delta-X, the CI comparison wasn't apples to apples. The consistency of speeds using under Delta-X brings into question the need for testing.
Now can someone tell me how you are going to print your 10 stop range of subject, as Adams does on page 50 of "The negative" and on page 54, onto grade 2 or grade 3 paper when a density of 1.3 above fb+fog (Adams zone VIII) will print as pure white on Grade 2 paper.
Are we to assume that the whole concept of getting zones 0 thru 10 onto paper without burning in is a myth put about by Adams himself?
Or maybe you're just not interested in looking at the "Whole system" which includes printing which I thought was the whole point of the zone system.
Thanks, yes I keep that in mind, it's one of the reasons why I won't use that estimated 1/6 stop adjustment in my own EI calculations.
But to compare to other people's Zone System test results, it helps to know the approximate CI for Zone System Normal - because the interpretation of those results always takes 0.10 density as the speed point. And that is displaced from the ASA/ISO speed point given the same film and same developer.
printing down (over printing) takes out a lot of micro contrast detail throughout the image becasue you are essentially fogging the micro highlights in the print
Or maybe you're just not interested in looking at the "Whole system" which includes printing which I thought was the whole point of the zone system.
Now can someone tell me how you are going to print your 10 stop range of subject, as Adams does on page 50 of "The negative" and on page 54, onto grade 2 or grade 3 paper when a density of 1.3 above fb+fog (Adams zone VIII) will print as pure white on Grade 2 paper.
Are we to assume that the whole concept of getting zones 0 thru 10 onto paper without burning in is a myth put about by Adams himself?
Nope, I'm now very bored of the zone system explained in mathematical terms. I don't think we'll ever have any common ground. Going to the depths you goto simply isn't necessary. It's of academic interest to a few but not me. Like gaussian optics, I studied it until I understood it, realised it was of no practical use to me in my everyday photography, promptly forgot it and got on with my photography. Sensitometry is exactly the same, boring for me now, I've learnt what I need of it and moved on.
18% grey card is munsel middle grey (number 5) which is a perceptual colour model. But he didn't think in terms of stops and I couldn't find anything which stated what the difference between each of his greyscale steps were.
But as we know, 18% is only 2 1/2 stops less than 100% so it can only be the middle of a 5 stop range at most.
My experience is that, with post 1980s cameras and lenses there is a very real tendency for the tests to deliver an EI of 1/2 box speed. However, this has much to do with more accurate shutter speeds, better control of internal reflection and CRUCIALLY multi-coating of lenses that dramatically reduce flare.
18% grey card is munsel middle grey (number 5) which is a perceptual colour model. But he didn't think in terms of stops and I couldn't find anything which stated what the difference between each of his greyscale steps were.
They are spaced perceptually uniform distance apart and are psychophysically based. As I've written before, I find Adams to be rather muddled on the relationship between the print Zones and scene Zones especially on how they relate with density.
There are a surprising number of patches that "might as well be black".
But as we know, 18% is only 2 1/2 stops less than 100% so it can only be the middle of a 5 stop range at most.
Adams knew that overexposure of negatives increased the average number of acceptable prints!
Mees published it in his book with a graph showing this. So did Haist. It is in his book. And, before he became ill, he was tracing Adams route through the Grand Tetons reproducing many of the Adams shots on modern film, both B&W and color.
Adams could not afford to miss a shot.
So, he biased the zone system to call for about 1/2 to 1/3 stop overexposure in order to increase the number of usable negatives when he was out in the middle of nowhere and could not go back easily to re-create a scene. This was to help you all out, not create trillions of disturbed electrons discussing why and wherefore!
Simple as that!
PE
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