Michael, now that you've achieved your goal. I'm going to show you why it's wrong. Not that you can't make quality prints with what you have, or that I'm suggesting changing anything you're doing. It's just that what you think is happening, isn't. What your test shows is not about film speed, but about testing procedures.
Originally Posted by Michael Hoth
The first two quadrant curve represents pretty much what you are observing. The film is processed to a CI 0.58. Zone I is placed at 0.10 over Fb+f. Zone III has a density of 0.39 and Zone VIII has a density of 1.24.
Zone System Placement copy.jpg
But you might have noticed that in order for Zone I to fall at 0.10, the exposure had to be increased by 2/3 stop. This is why Zone System EIs usually are tested at 1/2 the ISO. What would happen if the exposure wasn't adjusted?
Zone Placement 2 copy.jpg
This looks a little like your first field test. Take off another 1/3 stop of exposure and the results are almost identical. In effect, these two examples graphically illustrate your two tests. So, why doesn't the shadow exposure fall at the speed point when testing at the ISO speed?
In order for film speed to related to the metered exposure, the relationship between the speed point and where the metered exposure falls needs to be known. As most are aware, black and white film speed is measured in the shadows while the exposure meter measures the mid-tone. Because meters measure the mid-tone, certain assumptions about the shadows have to be made. The Zone System has Zone I falling 4 stops below the metered exposure. Tone reproduction standard model has it falling 4 1/3 stops below. The speed point of 0.10 over Fb+f; however, only falls 3 1/3 stops below the metered exposure point. Basically, the two methodologies use two different ranges when measuring the difference between the metered exposure and the speed point. Why is there a difference between the two when the shadows have practically the same relationship with the metered exposure?
Something else to consider, there isn't a direct correlation between a specific negative density and print reflection density. There isn't a target density for a Zone and not just because a zone is a range.
Last edited by Stephen Benskin; 04-02-2013 at 07:23 PM. Click to view previous post history.