Stephen, here's the Howard Bond test, often quoted and used to generate reciprocity formulas. I've gone through the tests in detail in the past, but just re-reading it quickly now, even in the intro paragraph he mentions the intent is to keep zone III constant.
Perhaps the reason people disregard densities below zone III when testing for reciprocity corrections for current films is that reciprocity failure is much less "exposure-dependent" than it used to be - ie there is much less contrast effect in reciprocity failure than with older films because areas of low exposure respond in similar ways to areas of high exposure. This is also discussed in the article.
Michael, thanks for posting the link to the Bond article. Iíve been able to skim through it a couple of times and Iím sure the results he got are fine. And while I havenít done a thorough read, there are a number of observations Iíd like to make about the testing.
Bond never explains why Zone III is the aim exposure for the testing. He doesnít address it in anyway. Thereís no theory to support the choice. I donít know about anyone else, but my first reaction is to ask why that point and why not another exposure or density point? He doesnít even make an assumption why Zone III should be used. What would his results be if he tested a stop lower, or two stops lower? Are we to simply accept his choice of Zone III without an explanation? While Iím sure his numbers will yield acceptable results, there is no evidence that they are remotely representational of the filmís reciprocity.
There are two other things that stood out. First is the testing exposure of 5 Ĺ stops above the metered reading (Zone X Ĺ). I guess technically the exposure was keyed to Zone IX Ĺ and given another stop for close up compensation. His results are pretty much what Iíve written about (most recently in the Large Format Forum). Itís easy to calculate the film plane exposure when you are using a camera as a sensitometer. Basically five stops over the metered exposure point will produce about a stop less exposure than most of the these type of methods assume. I havenít worked out the specifics of Bondís testing, but on the surface, this appears to be the case.
The other thing was the paragraph about camera flare. I had to go back and re-read how he was using the step tablet because I couldnít believe that anyone would have a paragraph on flare (and creating a device to boot) if the test was contacted. And I discovered I hadnít misread the testing procedures. The step tablet is indeed contacted. Not only contacted, but the target was a single toned white subject. This is about as flare free a test as one can get.
How valid is the test? Itís questionable at best in my book, but Iím sure the results are good enough for photography work.
Last edited by Stephen Benskin; 01-22-2012 at 10:30 PM. Click to view previous post history.
Thanks for your thoughts on this, Stephen. It has puzzled me for some time. The simplistic assumption I make is that since the shape of the curve for most current films does not change nearly as much with reciprocity failure as it did in the "old days", Bond and others reason that by maintaining a stable zone III density, the densities below also remain pretty much where they were as well. I don't know, but that's really the only logic I can find in the approach. But even still, why zone III and not zone II or I, after establishing EI with a zone I density in the first place. Zone III is usually an important value for most zone system users. But for it to remain that key shadow point for retaining good detail when reciprocity failure takes over requires that the densities below zone III remain the same as under normal reciprocity conditions.
Anyhow, food for thought.
Thanks again for the insight.
Low level reciprocity only affects the lower luminance values. The reason why development needs to be reduced when compensating for reciprocity is because the higher values aren't affected by the latent image regression and build additional density with the additional exposure required to create adequate shadow density. The further the exposure is from the shadow, the less of an affect reciprocity has on it.
What Bond needed to do was to first prove that the use of Zone III was the best point to test for reciprocity. He would then have a strong foundation from which to present his conclusions.
I believe it's important to do a little critical analysis with any written material or claim and not just take the author at their word. There's too much argument from authority used in and around the photographic community and too many statements and claims made without any proof or supporting argument. I'm consistently tempted to simply reply "prove it" to many posts here on APUG. Ansel said it was so just isn't enough.
I'm currently doing a little critical analysis of a few charts and graphs in the thread Hiding in Plain Sight. I think it would be a good idea to make it a common practice here to do more critical analysis of articles, graphs, information from websites, or photographic theories or concepts. Such discussions would be a welcome change from the ubiquitous what developer to use with what film threads.
The Bond article is a good start. Too many of these types of articles tend to be heavily into the how to and light on the reason why. Shouldn't we be also talking about the why?
Why should you force feed a "why" analysis on someone else's results........if for yourself, that's fine.
Originally Posted by Stephen Benskin
I have a camera and a step wedge-----and I have a text that I use that has taught me "how to" effectively carryout tests for EI. My tests have been hugely rewarding and have helped me improve my photographic abilities exponentially. "Why" should I let you try to convince me that I just don't really understand what it is that I am looking at? There is absolutely nothing wrong with "how to" as a point of departure for going forward and utilizing what you have learned for yourself. The results are put into practice that have yielded such good negatives, speaking for myself that is.
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Stephen, regarding low level reciprocity, one of the things Bond argues is that with current films reciprocity failure is much more linear than it once was, or may have been. He finds it is not as biased toward low luminance values as we think it is and so, surprisingly, he finds much less development compensation is typically required for long exposures - at least with the films he tested. He found the contrast increase during long exposures is actually minimal with these films. People often report that this is how enlarging papers behave when reciprocity failure kicks in - ie you need longer exposure times, but there is no significant increase in contrast. I'm not sure about any of this, but it's interesting.
Regarding asking why, I think as long as we don't get too bogged down in levels of precision unattainable outside the lab, the discussion can definitely be interesting. Knowledge is a good thing. Personally I'd agree we tend to follow the technical writings of well known photographers too blindly. Mostly, things seem to work ok. But some writings really need to be challenged (in my opinion). Barnbaum's book is a good example, one I have criticized before on here. He might be a good photographer, but I don't think he "knows what he's getting" in his negatives. He's adjusted for all that with experience (perhaps without realizing it), but he shouldn't be writing about densitometry and the zone system. He's dead wrong about quite a few things.
Last edited by Michael R 1974; 01-23-2012 at 10:46 AM. Click to view previous post history.
It's called a discussion or an analysis. Why do it? Because we are not sheep or robots. Following something blindly may be fine for some, but not everyone. Why should you feel the need to repress learning?
Originally Posted by CPorter
Come on Chuck, don't get defensive over this. I'm sure you started with the standard Ansel Zone System test until you discovered the Schiffer test when you asked yourself why one may be better than the other. It's all just a matter of degrees. If you're happy with your the results of your test, great. Many people are happy with their results without doing any testing at all. It's up to them. Being satisfied with something doesn't make it correct or perfect. What's wrong with discussing the strengths and weaknesses of a technique or methodolgy. Then we can use our own minds and maybe create something even better.
And if you disagree with the analysis - prove it wrong. Let's have a lively discussion!
If this is something he's found, great. He should show the data. He needs to prove it.
Originally Posted by Michael R 1974
Discussing Barnbaum's book is what I'm talking about. I believe that's the kind of thing that leads to healthy and profitable discussions.
[/QUOTE]Regarding asking why, I think as long as we don't get too bogged down in levels of precision unattainable outside the lab, the discussion can definitely be interesting. Knowledge is a good thing.[/QUOTE]
I agree, but asking why leads to informed discissions. Also, without questioning, how can you determine where the that level of unobtainable precision is? As my understanding of the exposure has grown, it has given me more freedom not less. It helps me understand the limitations and variances of a system or what is capable in practice and what is not. What is really a factor to watch out for and what is not.
Last edited by Stephen Benskin; 01-23-2012 at 11:18 AM. Click to view previous post history.
Bond does show some curves/data in the article to support what he's saying regarding contrast with long exposures. Are they accurate? I don't know.
Here's a point of criticism on the diagrams.
OK it's just a typo but it's obvious the caption doesn't match the diagram.
What it should say is...
II B Reversal, Pictorial.
H-bar is found from the average of two log H values, one
at 0.2 above base + fog, the other at 2.0 above base +
fog or at the point of tangency...