Sexton doesn't use such hard rules for shadow placements. Generally he rates his TMX at EI 64 (for normal development) and uses zone III for shadows, although he will sometimes put them higher, even up to zone V depending on the scene lumincance range and the desired negative densities.
Barnbaum is the guy who says zone IV is good and zone III is wrong. He substantiates this with an imaginary, very inaccurate H&D curve (not entirely surprising since he is proud to say he has never owned a densitometer). In my opinion, he's a good example of a guy who "doesn't really know what he's getting" in the negative but has simply dialed in his exposure, development, and subsequent printing procedures with time and practice. Nothing wrong with that at all - except when you write a method text.
Each zone separated by 0.3 log exposure units i.e., one stop differences. Just curious here........what is wrong with that?
Originally Posted by Stephen Benskin
The diagram is slightly simplified because it leaves out the effects of flare, which can make shadows land higher in density on the film than you previsualized.
Originally Posted by CPorter
Flare is exposure applied over the whole sheet of film. It messes up the neat 0.3 exposure units.
You can visualize flare exposure more easily using an arithmetic scale instead of logarithmic scale. Arbitrarily call Zone I = 1, and arbitrarily call it one stop of flare. Then you wind up with this series and you can see that the shadows are tweaked more than the middle tones, and above that you can just as well ignore it.
Zone I = 1 + Flare 1 = 2
Zone II = 2 + Flare 1 = 3
Zone III = 4 + Flare 1 = 5
Zone IV = 8 + Flare 1 = 9
Zone V = 16 + Flare 1 = 17
Zone VI = 32 + Flare 1 = 33
Originally Posted by Bill Burk
I liken flare to the effect of pre-exposure, except that pre-exposure, when given, is intentional and controlled where as flare is always present, random in intensity, and very hard to quantify and that it is applied over the entire sheet of film. Like pre-exposure, adding one unit of flare, in your example, Flare I, amounts to proportionally less and less increases in negative density moving up the scale of zones. Flare's potential affect in the lower zones is given, its actual significance quite negligible in many instances IMO. I always shield the lens best I can, I may sometimes, if ever I feel it can pose a more significant problem, make just a small exposure adjustment.
In terms of evaluating a curve for determinatin of EI, however, I don't see much point in including some factor for flare, but that is just me, not at all saying it's pointless for anybody to do so. I can only report that not including it, seems not to have had any dramatic influence on any negative I have ever produced since becoming proficient in my use of the ZS and the associated testing. All of Ross's curves presented on that link have been adjust for EI (although the example doesn't indicate what they are, only that they've been adjusted), hence the reason that they all originate from the same location at Zone I. I ask myself how a flare factor could influence my evaluation of those curves for applied photography (or my own for that matter), I always arrive at the same answer, it doesn't, but I understand its potential affect for any given exposure, which is what I think is ultimately more important. I find the overall discussion interesting and I appreciate the knowledge base.
Flare not only changes where the shadow exposure falls, but also reduces the scenes luminance range at the film plane. In Bill's example flare changes a 1:32 scene into a 2:33 scene at the film plane. 2:33 can almost be reduced to 1:16.
Take another look at the Kodak diagram from post #1.
At the top is the subject. It has a range of 7 stops or log 2.10. Flare reduces this range within the camera. Here they call it the Optical Image. It now has a range of 1.85 logs or a touch over 6 stops. The film is then processed for the six stop range, and not the original 7 stop range. Mathematically it's very simple. To find the illuminance range of the subject at the film plane, you subtract the amount of flare from the subject luminance range. In the case of the Kodak diagram: 2.10 - 0.25 = 1.85.
The next example is from Photographic Materials and Processes.
I was told it was the text book for first year students at RIT. Quadrant I, the lower right quadrant, represents the camera image. At the top are the Subject Values or original subject. Here the stops are equally spaced. Flare from the optical system changes the relationship of the original subject values. The values that strike the film, the dividing line between Quadrant I and Quadrant II, are no longer equally spaced as flare has compressed the lower values.
A common mistake when interpreting a film curve is to apply the equally spaced values of the original subject along the log-H axis instead of the values from the camera image.
When does flare not exist? It is with the contacting of the step tablet in testing conditions. In order to have a realistic representation of how the subject is reproduced on the film curve when shot with a camera, flare must be incorporated when making interpretations. So, no flare when creating the characteristic film curve. Flare when interpreting the film curve. It's the difference between testing and interpreting.
Post #13 has the CI / Negative density range chart that Kodak uses. The only way for the values to work out as they are in the chart is to apply a fix flare value of 0.40. Flare is factored in. Film manufacture's development recommendations have a value of flare already calculated into it. Film speed has it factored in. It's just that it's extremely hard to notice something that is normally there. Flare only becomes noticeable to most people when it is excessive.
With a front lit scene, 80% of the flare comes from the subject itself. Shading the lens will only help control the other 20%.
The answers are out there hiding in plane sight for anyone willing to look for them.
Last edited by Stephen Benskin; 02-13-2012 at 10:27 PM. Click to view previous post history.
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It's isolating the variables and incorporating them one-by-one wherever possible. I agree it is hard to estimate flare.
Originally Posted by Stephen Benskin
I am starting to think that keying development on higher zones (Alan Ross' self-titled heretical approach) may have its advantages. You probably have a higher probability of "calling your shots" when you try to control somewhere far away from the out-of-control low Zones.
Though I see the merit in Ross' heresy, I still spot my shadows for Zone II, and alter my EI to make Zone II fall on the film curve where I want Zone II (so I include flare). I haven't made my mind up where I want that to be, and this thread is guiding me towards that decision. Today my TMY-2 EI is 250 and it seems to be working out.
Originally Posted by Stephen Benskin
It has just always been my belief, that the image brightness range is more often than not, pretty close to the subject brightness range (obviously not perfectly in any instance) with a great deal of that owed to high quality multi-coated lenses. Now, although there is nothing at all from me to scientifically substantiate that in anybodies mind, it is quite emperically accepted in mine. I simply believe in the end, that a greater percentage of flare is mitigated than what is being discussed.
Your're right, I guess there is a lot that can be hiding in plain sight, but with that being so, the need must arise to seek before there's a desire to go searching.
Like I said, flare and many other factors are incorporated into photography. Photographic scientists and engineers have worked hard in order to make photography work without having to understand it. As I've shown, flare is also incorporated into the Zone System, albeit unintentionally. For those wanting to discuss and understand the photographic process with all the factors that come into play within the process, they should be part of defining, analyzing, and explaining the process else there will be a gap in understanding how it works.
There's an easy way to extrapolate what is considered normal flare. Kodak considers a CI 0.58 for normal processing. The LER for the middle of a grade 2 paper range is 1.05. The average scene luminance range is 2.20 logs.
1.05 / 2.20 = 0.477
Take off a stop from the luminance range
1.05 / 1.90 = 0.553
Close but not exact. Take off another 1/3 stop.
1.05 / 1.80 = 0.583
So, Kodak considers the average flare to be 1 1/3 stops. Flare is part of their normal.
Flare helps make sense of the photographic process.
Last edited by Stephen Benskin; 02-14-2012 at 09:59 AM. Click to view previous post history.
Stephen, I've brought this up before but not sure if we really discussed testing methodology. When I do film tests for EI, development times etc I do it in-camera, and photograph a very brightly (and uniformly) lit white card. Picture a makeshift copy stand sort of setup. I always thought this would effectively factor in some flare, and be a better way of testing for my applications than step wedges. Although admittedly it is not a perfect test, do you think I'm getting at least some flare factor?
You are effectively factoring in shutter speed and f/stop when you do a camera test.
Originally Posted by Michael R 1974
The uniform lighting and low exposure placement reduces flare when you do a test like that.
Flare is going to hit you when you take a normal picture and the bright sky lights up the surfaces of the lens and interior of the camera. Then you end up giving the shadows an additional stop or more of exposure than you thought you were getting.
You can test for your camera's flare with a "black box" included in a variety of scenes.