Mr. Bill, we're at an impasse. I believe we are arguing over an issue of personal preference and from two different areas of use. I'm going to go back to the Michael's question on Fractional Gradient speed.
Stephen, if you don't mind the diversion back to speed determination, I'd like to list some questions and observations based on the papers you sent me. At the outset I must admit at first the graphs on page 325 of the Nelson/Simonds really surprised me and kind of turned my hypothesis upside down regarding the best speed method for my work. As I went through your paper the issue became a little clearer to me, although I still have questions. And I might now have shifted my preference back to fixed density vs fractional gradient when it comes to developing for reduced contrast. Still not entirely sure. First a few questions:
1. In Nelson/Simonds, they state the interval 1.3 Log E (H) interval was chosen “in order that D2 would be approximately equal to the highlight density in the first excellent negative of an average scene”. Can you explain this?
2. In your paper you state the ISO speed point falls 3 1/3 stops below the meter calibration point and shadow exposure falls 4 1/3 stops below. I’m confused by both these intervals.
Now to the “issue” I alluded to, which your paper addresses in the example illustrating how with lower or higher than average delta Ds the Delta-X speeds rounded to the same number (the “compensation effect”).
It occurs to me, the print evaluation studies originally used in deriving 0.3G involved exposures of average scenes. So, to me, it would mean in the context of the tests, developing the films to lower gradients (for example) would have constituted “errors” to be corrected with an increase in paper grade – rather than deliberate attempts to accommodate a higher than normal subject luminance range. This could explain why I was initially startled by the six graphs on p.325. Before going into this, I had actually expected at least some of the print judgment speeds and 0.3G speeds to be lower than the fixed density speeds (eg: the long toe, low gradient curves). But this is the opposite of what was concluded in the print evaluation studies. While the math made sense to me, intuitively the graphs just didn’t look right – unless one simply increased the paper grade to effectively normalize say the bottom two curves in Fig.2. This is my take on why the fractional gradient method is not more concerned about a precise contrast. A constant relationship of 0.3G seems to work in print judgment tests, apparently regardless of how low the absolute toe contrast is, because a correction via increase in paper grade would bring both the toe G and average G up. I think this is sort of a different way of saying the same thing as the possible explanation you outline in your paper for why fractional gradient is not more concerned with a target contrast, and why the Delta-X film speed stays relatively constant with deviations in delta D.
Another possible explanation for why ZS testing typically results in lower EIs than ISO speeds – even when targeting a normal gradient – concerns the shape of a typical modern film curve in relation to the Delta-X criterion of .8 delta D over a 1.3 log H interval. But before I get into that, I really need a better understanding of the intervals in question 2 above. I think those are key to my understanding.
Hopefully I’m not too off the rails here…
Thanks again for bearing with me. I'm not the quickest at "getting" this stuff.
Last edited by Michael R 1974; 03-09-2013 at 08:41 PM. Click to view previous post history.
Reason: typos and clarity
I think using higher grade of paper on lower gradient negatives amplifies the toe, giving you the "ability" to reach more into the toe. Thus making film "speed" faster than intuitive. You would think underdeveloping would cost speed. But the ability to amplify keeps that from happening.
Originally Posted by Michael R 1974
I also think the Delta-X is meant as a means to estimate 0.3G, if you can find 0.3G by computation, then by all means find 0.3G
Why does ZS come up one EI lower than ASA/ISO? I think deserves a thread of its own.
p.s. I started a thread.
Last edited by Bill Burk; 03-09-2013 at 03:10 PM. Click to view previous post history.
Reason: linked thread
That's why I started this thread. Understanding the speed methods and ISO is key to bridging the disconnect with ZS methods. I think I'm getting closer!!
I may need to double-post ideas as they come together...
I like to keep in mind Ansel Adams developed the Zone System before the print studies were done. He had no knowledge of the 0.3 Gradient.
He also aimed to correlate prints to the Weston Meter. Thus he arbitrarily labeled 10 Zones (8 if you only count the "Textured" Zones) instead of using scientifically more accurate 7 2/3 Stops.
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Adams was in communicaton with Mees.
Originally Posted by Bill Burk
Last edited by Stephen Benskin; 03-09-2013 at 05:09 PM. Click to view previous post history.
Ah, good, now I have to reconstruct a timeline! But it seems 0.3 G isn't factored into ZS.
Originally Posted by Stephen Benskin
Fair enough! Michael, sorry for the extended diversion, I lost track of your original question.
Originally Posted by Stephen Benskin
I was thinking of a (perhaps) clearer way to explain what I meant in my post above, which is probably too wordy. I think the fractional gradient constant 0.3 produces the first excellent print under all/most development circumstances when the original scene has a normal luminance range. If on the other hand, one deliberately reduces development to manage a scene of higher than normal subject contrast, the first excellent print might only come from a fractional gradient relationship of 0.4G or 0.6G etc. In other words, the fraction, rather than being a constant, could be related somehow to the subject luminance range. Or said even another way, the fraction could be inversely related to G. This would be a possible bridge between print judgement speeds (or fractional gradient speeds) and the variable EIs people arrive at in their ZS testing using a fixed density criterion with +/- development. The speed methods deal with a standard, while applied densitometry systems like ZS deal with the management of scene luminance ranges.
Note this concerns film speeds for different Gs, not the difference between a normal ZS EI and ISO speed.
Again these are just some preliminary thoughts after reviewing the papers.
Mr. Bill, didn't mean to imply the tone reproduction discussion isn't relevant. Sorry about that.
Last edited by Michael R 1974; 03-09-2013 at 08:38 PM. Click to view previous post history.
Michael, lots of questions. I'll get into them presently, but one thing I see is that you are wanting to think through the reasons why one methodology is superior to another. Unfortunately, you don't have all the information. Here are the papers involved in Jones' testing of the late 1930s and early 1940s. (And they purposely tested negatives derived from a variety of luminance ranges.)
Originally Posted by Michael R 1974
Jones, L.A., Russell, M.E., Minimum Useful Gradient as a Criterion of Photographic Speed, JOSA, vol 25, Dec 1935.
Jones, L.A., The Evaluation of Negative Film Speeds in Terms of Print Quality, Journal of the Franklin Institute, vol 227, n 3, March 1939.
Jones, L.A., The Evaluation of Negative Film Speeds in Terms of Print Quality, conclusion, Journal of the Franklin Institute, April 1939.
Jones, L.A., Nelson, C.N., A Study of Various Sensitometric Criteria of Negative Film Speeds, JOSA, vol 30, n 3, March 1940.
Jones, L.A., Condit, H.R., The Brightness Scale of Exterior Scenes and the Computation of Correct Photographic Exposure, JOSA, vol 31, n 11, November 1941
And in addition to Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials is what established the 1960 ASA film speed standard - Nelson's Safety Factors in Camera Exposure.
safety factors in Camera Exposure.pdf