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.
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?
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.
I'll get to Dunn here in a second.
Originally Posted by Stephen Benskin
What I'm getting at is that; for a given film, given a certain amount of exposure, and processed in a given process, we get a given result.
The only real controls we have over the curve are " which film" and "how to process it". Once we decide on these the shape of the curve becomes a given.
It seems to me CPorter is describing not just the print range he expects to put on paper, but also, given the tight limits he suggests, where it will land on the paper. In fact the specific negative density range he picked, roughly .1 to 1.3, is only truly relevant if the target paper and enlarger exposure are givens. I'd even hazard a guess that CPorter may have normal/starting enlarger settings where he can straight proof his negatives on his normal paper. He may even consider negatives that don't fall normally onto the paper to be over or under-exposed.
Tight exposure and processing control of our films makes darkroom work easier by placing our subject matter where it will carry through nicely to the paper under "our normal conditions" with little or no adjustment.
This is where I come to Dunn's thoughts.
It appears to me that CPorter, like many others, uses the the general precepts described in section B "still monochrome photography" of chapter 1 in the 3rd edition; the darkest part of the subject matter defines the exposure settings and the difference between the darkest and lightest defines the processing.
My sensibilities and preferences are more as Dunn describes in section C "motion picture and colour work".
While the exact placement of subject matter from zone I and VIII in the scene appears very important to CPorter for his prints, that style of subject placement is normally a secondary consideration to me. The subject matter I want to land perfectly on my paper are mid to upper-tone subjects like faces. Chasing face exposure settings in the enlarger from frame to frame in my printing is truly frustrating for me. I do also expect a certain contrast rate for my shots but most times I don't care at which point specific subject matter ends up in zone III or zone II.
For any important shot I peg my mid-tones to the curve as carefully as CPorter does to his chosen peg.
I don't believe that CPorter and I disagree about the shape or sensitivity of a given film curve, we simply have differing expectations of what we expect to peg in our prints.
For a second there, I thought you were going to tell me to expose for the shadows and develop for the highlights. I don't have time to go into this now, but I never said that there shouldn't be consistency in exposure. Your argument is a straw man.
Two quick comments about the WBM examples. In the Film Test Evaluation chart, the actual log-H should be relative log-H. And maybe I'm missing something, but the other example has the log-H range as 1.21 (7stops /Zones) but indicates this covers Zone II to Zone VIII or 6 stops in the Δ1.20 density range, which is actually on the high end for a Δ2.20 log-H luminance range.
Well, it's the basic expose for the shadows, develop for the highlights scenario............It's primarily the "placed" luminance value in the scene that determines the camera settings (not always the darkest part)..........and, of course, it's where the most desired textured or slightly textured high value "falls" on the gray scale that dictates processing. By controlling the shadows with exposure and highlights with development, the mid-tones are sure to fall as predicted on the gray scale relative to the "placed" luminance value and be quite manageable and easily manipulated in printing. That's why I don't bother with concerning myself with specific density values between the "effective" speed point at Zone I and the calibration value that defines my "normal" development time, which is a target density of 1.3D at Zone VIII.
Originally Posted by markbarendt
It meant he was over simplifiying. Seriously Chuck?
Originally Posted by Stephen Benskin
I'll second what Stephen says. I'd be happy to print from the negative you achieved. The range would fit my paper, and the shadow detail gives plenty to work with. I've had similar results where I tested and pegged the shadows, yet they came up above the density I predicted.
I also like to understand what is going on, but I try not to let my (mis)understanding of why... get in the way of shooting. So keep doing, and let the theory discussions be the fireside chats that you mull over in spare time.
Yeah, seriously...............I take "almost" nothing for granted in these forums....it doesn't pay. I'm sure Mark is not concerned about the post, if he is, he can let me know.
Thank you Chuck. You are right I'm not concerned. In fact it is interesting understanding how others think.
Originally Posted by CPorter
I must apologize. With all the running around this morning, I didn't take enough time to thoroughly read Chuck's post and I misinterpreted who the post was directed at and it's intention.
Mark, I looked through that chapter on Dunn and it was about metering techniques. I believe we are discussing two different subjects. I'm talking about how some believe Zone V has to be at a specific negative density. Curve shape makes that impossible. Or when someone interprets their film as overexposed just because it prints a little light using a just black proof. Simply put, that's bad theory. And I think it can be conceptually restrictive.
I've added a few things to one of the two quad examples from post #201. This example has it's exposure based on the ISO. Zone V represents the metered exposure. As the example shows, the equation of metered exposure is 8 / ISO and the example uses a 125 speed film so the metered exposure is 0.064 lxs. Speed point falls Δ 1.0 log-H units below at 0.8/ISO or 0.8 / 125 = 0.0064 lxs. So in this example, the exposure was perfect for a film that has an ISO of 125. Zone I falls below the speed point at 0.0041 lxs.