Yes, but that isn't the solution to the problem. If you had two negatives from the same scene, one processed to produce a NDR of 1.05 and the other a NDR of 1.25, it would eliminate any psychophysical differences, but you are still left with the problem that the negative with the NDR of 1.35 is too large for the paper parameters.
Originally Posted by Bill Burk
Hint: Work on the CI questions.
Last edited by Stephen Benskin; 09-09-2011 at 11:01 PM. Click to view previous post history.
Wait, your negative A is 0.61 CI which is really close to the prescribed 0.58 CI for a 7 1/3 stop subject brightness range onto Grade 2 paper. Yet paper B shows the resulting negative range of 1.35 would stink for Grade 2.
Is the bottom line then?... The reason 0.58 CI is Normal on the CI charts for Grade 2 and 7 1/3 stops is because you will NOT get a 1.35 negative range (because of flare and optics). And that still it is OK to exceed the LER 1.05, (guess maybe you really get 1.15)?
I hate to say this, but over the last 60 years or so, I have known literally hundreds of "famous" photographers and truth to tell, not one of them used the zone system to my knowledge. And, when it gets down to it, the zone system is a reduced form of Densitometry and Sensitometry. Nothing more than an H&D curve with a glorified name.
I've said this before in other posts. Sorry. I probably should not say it here and I will take a lot of heat over this.
So close. (As a matter of fact, I used CI 0.61 because I was working with the Zone Systems 7 stop luminance range.) Let's not forget both film curves are same. They have the same CI.
Originally Posted by Bill Burk
Could you walk us through the different variables for the CI 0.58 determination?
Not from me, although I am a zone system user, and I enjoy Stephen's insightful discussions. For me the zone system as described by Adams is a nice way of relating subject brightness ranges to H&D curves, as a framework for better understanding exposure and development control. That's all it is, really. That said, I still find Stephen's insights interesting because they highlight the potential pitfalls in generating and interpreting densitometric/sensitometric data. Luckily our tools allow for quite a bit of noise - in the end it comes down to our printing skills.
Originally Posted by Photo Engineer
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Densitometry and sensitometry are part of very technical approach to the zone system. The zone system can also be approached very effectively in a craft way by experimenting with bracketed exposures and bracketed development.
However, both approaches are only a small part of the zone system. The key is pre-visualization of the desired result. Once the visualization is made, then steps can be taken and choices can be made. Lighting can be changed (though often it can't), exposures chosen, development prescribed, dodging and burning contemplated, merging and masking images considered.
Ron, thank you. I'll have your back all the way on this. They are really the same but just use different terms; they both use the same physics; therefore they both should equate.
Originally Posted by Photo Engineer
As the level of frustration seems to be rising, I would like to remind everyone of a few comments I made in an earlier post. The question was about the "correct representation." I could also have said correct presentation of the facts. Remember, both curves are identical and represent a 7 stop luminance range.
I also said "the key is in the interpretation of the data, and a large part of that is having a good grasp of certain principles and asking the right questions." This thread is about the importance of interpreting the testing data. It's not about one system being better than the another (as they are basically the same). I'm using an apparent discrepancy as an example of how problematic misinterpretation of the data can be. And the misinterpretation of data is usually the result of not being aware of and not factoring in all the variables involved.
Last edited by Stephen Benskin; 09-10-2011 at 12:02 AM. Click to view previous post history.
All this Zone System talk got me fired up so I was in the darkroom tonight running a set of tests on a fresh box of film that came in today. My tests will have no flare (sensitometer). I will be drawing Zone System roman numerals on the curves. I will be using a Zone scale on my lightmeter. (Mostly to spot the shadows and place them on a certain Zone).
Okay, time to bring this to a conclusion.
CI or any average gradient simply tells you want the film is doing. It’s about input and output. A CI 0.50 says that if one unit goes in, ½ unit comes out.
It’s importance in this thread is that it is a different way of approaching the problem. Just having a NDR doesn’t tell you anything about the shooting or processing conditions. If you have two of variables, the third can be determined.
It’s easy to extrapolate the average gradient for the Zone System variables. The Zone System provides the NDR 1.25 and the SBR of 7 stops (2.10 logs).
1.25 (NDR) / 2.10 (7 stop SBR) = 0.595
The importance of Kodak’s CI chart was that it provides all three components involved in the CI equation to practice with, input, output, and gradient. The reason why I added the Xtol pamphlet was to provide an example of what Kodak considers to be the CI for normal. They had it as 0.58. On the Kodak CI chart, that fell under a 7 1/3 stop SBR and a 1.05 LER.
1.05 / 2.20 = 0.48
As that doesn’t equal 0.58 there must be another variable involved, and that variable is FLARE. Now much flare:
1.05 / 2.20 – 0.40 = 0.58
People forget that there are four different elements of "contrast" to consider in the photographic processes. There's the Log subject luminance range of the original subject, the negative density range, the print LER, and the exposure range of the camera image. What the film sees it the camera image, not the tones of the original subject. The input is the combination of the affects of flare on the SBR and not the SBR alone.
Flare is the answer to this thread.
Curve A is the correct representation of reality in that it incorporates how flare changes the log-H range. Otherwise the two examples are the same. They will produce the same negative density range for the same subject. The way we know that is because of understanding how gradient works and not relying only on the negative density range as an expression of the conditions. NDR is only half of the gradient equation. Alone it tells you nothing about the film process conditions or the shooting conditions.
So, the answer is
1.25 / 2.10 = 0.59
1.05 / 2.20 - 0.40 = 0.58
The two examples are the same. The only difference is one is misinterpreting the data.
The Kodak CI chart show one of the advantages of using average gradient. You can easily determine the all the processing aims simply by input a few variables. Together with a Time/CI Curve, it’s a great tool (Development chart attachment).
Keeping with the topic of understanding all the variables and the advantages of correct interpretation, is the idea of the type of flare model to use. There are fundamentally two different models. The fixed flare model which the Kodak chart uses, and the variable flare model where the value of flare changes as the luminance range changes.
The fixed flare model is easier to generate, but the variable flare model is more representative of shooting conditions. In general, as the luminance range increases, so the level of flare. As the luminance range decrease, so does the flare factor.
With a fixed flare model, the CI indication tends to be excessive with + 2 and +3 development, and quickly flattens out with -2 and below. This isn’t the case with variable flare, but according to psychophysical aspects of tone reproduction theory, the perception of quality in the extreme processing ranges could still be a problem.
According to Jones, “Our analysis of the statistical print judgment data revealed that for maximum yield of high quality prints a surprising rule should be followed: For the soft papers, the density ranges of the negatives should in most cases exceed the sensitometric exposure range of the paper (read LER); whereas, for the hard papers, the density ranges of the negatives should in most cases be less than the sensitometric exposure range (read LER) of the paper.”
Because of this I came up with a third model which I call the practical flare model. It basically splits the difference between fixed and variable flare models.
I’ve attached a chart comparing CIs for various models. Sounds to me like all this technical stuff can give a person some serious creative control over their materials.
Man this zone system can be complicated to hell n back with equasions n mathamatical terms. We're artists not scientists, we don't add 2+2, we count fingers or F stops!
50 years of using the zone system, I've ledarned that the oversimplified version makes more sense. I was always told, as many of us were, by an old photoggrapher friend...
"Expose for the for the shadows, develope for the highlights."
I think we've all heard that one before and it's right on the mark, it's called the Zone System.
Set the camera for the shadow reading, take the meter reading difference of the hightlights, and since you've done the tests you know what the Normal N, N1 N2 N3 and N-1 N-2 N-3 times are so you don't block up the hightlights. jot down the N reading and it all falls into place as expected.
BUT.. you have to do all the hands on tests to know exactly how all this relates to the final print or you are just wasting too much time with a calculator when you have 10 perfecly good fingers to use for making pictures.
Anyone can make a Digital print, but only a photographer can make a photograph.