Of course manufacturer's speeds are correct, I rely on that. But my negatives have been too thin, to me it becomes a question of placement.
Originally Posted by 2F/2F
Here is my placement plan for now (subject to change)...
-sensitometry to plot curve family and (thanks to this thread), time/CI.
-target paper LER (still need to do paperwork).
-enter half the proven speed at 0.1 as meter EI (subject to change).
-use Zone System roman numerals metering the scene, placing values and checking falls. For example placing shadows on Zone II and caucasian faces on Zone VI.
Dale, you've made a good logical argument but there are a few details that need to be included and they will lead to a different conclusion. If you go back to the beginning of this thread, one of the concepts was the correct interpretation of the data requires a proper understanding of the principles involved. With aim NDR, it was interpreting flare from the data in a non-flare test.
You're correct that the information that comes with the grey card recommends opening up 1/2 stop when metering the card outdoors. You are also correct that, given all the conditions of the standard model of exposure, 18% reflectance is 1/2 stop brighter than the metered exposure point of 12%.
What you left out was there is a distinction with using a grey card as a test target and using it to base the exposure upon. The exposure meter wants to make an exposure at the film plane of 8/ISO no matter what it is pointed at. It doesn't matter. Whether it's a 18% grey card, white card, or whatever, the metered exposure will fall at the same point on the curve. Meter an 18% grey card or a white card and stop down a stop and the exposure will fall 0.30 log-H units to the left of the metered exposure point. Therefore, the reflectance of the target card has no affect on the placement of exposure.
What is important is all the tones surrounding the reflectance of the object metered and where they will fall on the film curve in relation to the metered exposure.
The concept of exposure is to place the exposure values of the scene on the film curve where there is sufficient separation (gradient) to produce a quality print. This is why determining the minimum point of exposure (fractional gradient) where this can happen is a vital component in the determination of film speeds.
For an average scene, the shadows fall 4 1/3 stops below the meter exposure point. As we know, no matter the luminance of an object in a scene, the exposure meter will want to make it the same exposure value. The difference between shooting a card for a test and metering it to photograph a scene? The test card is by itself. The card used for photographing a scene has the scene attached with its range.
If you meter a white object and use the metered exposure, the white card will fall at 8/ISO. As most of the rest of the scene is darker, it will fall to the left of that point on the curve. We know that the fractional gradient point falls approximately 4 1/3 stops below the metered exposure point, so anything below that will have degraded quality.
The shadows in an average scene fall between 4 3/4 and 5 stops below 18% reflectance. In order to have the shadows fall at a point for good reproduction, the metered exposure must be adjusted by 1/2 stop. That's why you open up when metering an 18% grey card to photograph an outside scene.
The instructions that come with Kodak's Neutral Grey Card also say not to adjust the exposure when using the card to determine the exposure for a copy or 2 dimensional set-up. Why? It has nothing to do with mid-tone reproduction. It's because the blacks from art work don't fall as far down on the curve as the exterior scene's shadows.
Other than making sure there's sufficient separation of the shadows, there is no placing of tones on the negative. The negative is the intermediary step in the process. You just need to have a negative that separates all the luminance values from the scene and has a density range that closely matches the paper. The rest is misinterpretation on how it works.
I've attached two fun examples. The film curve shows a long toed film (TXP 120) and a medium toed film (TX 135). They are processed to the same CI. The metered exposure point falls 1.0 log-H units to the right of 0.10 Fb+f. The two films have different densities at this point. It would take an additional 2/3 stop with the long toed film for the densities to match.
The four quadrant curve has the reflectance of Zone V equaling 12%. Because of the various factors of the film and paper curve shape, and the luminance range interact, it is possible to meter a 12% Zone V reflectance and have it print as a 18% reflectance. And this is with strict computer curve fitting. Sight differences in print exposure will easily shift the mid-tone around enough to concluded anything you want about Zonal relationships.
Last edited by Stephen Benskin; 09-16-2011 at 02:04 AM. Click to view previous post history.
I just found this little passage on page 95 of the fourth edition of Beyond the Zone System. Let me know if it sounds familiar.
"Now, because you will want to produce negatives that print comfortably on your chosen paper, use the SI value (read LER) you calculated in your paper test to locate IDmax, but do so only after making one further adjustment.
This final adjustment is necessary because your curve data are based on a no-flare test condition, but you'll be applying the data to camera exposures that invariably involve significant amounts of flare. We'll discuss flare in greater detail later, but at this point, you should realize that it general effect is to increase the negative's IDmin value and decrease it DR. In other words, it boosts the negative density and reduces contrast, especially shadow contrast. For example, if we assume an SI value of 0.90, your test data may indicate that a negative of some subject will have an IDmin value of 0.06 and an IDmax value of 0.96 (found by adding an SI of 0.90 to the IDmin), but camera flare will typically alter those values to something more like IDmin = 0.15, IDmax = 0.97, for an effective DR of perhaps 0.82."
"At this point, we can only guess at the amount of adjustment necessary, so we'll assume a typical value and make the compensation by increasing the SI (LER) value by 10%.
For example, if your SI (LER) value is 0.90, multiply it by 1.10 (110%) to get 0.99, and add that to 0.06(the IDmin value) to get 1.05. Then mark each curve at that level: 1.05 over B +F."
Davis has, in effect, done the same work around as the Zone System (NDR 1.25 example), except he made a conscious decision to do so by understanding the theory and the Zone System just lucked out. I, however, have the same problem with Davis approach as I do with the Zone System in that it doesn't explain what is really going on in reality. The paper's SI (I hate that he never update his terminology as well as just made some of it up) or LER, is what it is.
Attributing the influence of flare to the LER instead of the log-H range is conceptually wrong and misleading. It can create a problem with proper interpretation of the conditions and results, and it can be misleading when communicating the conditions and results with others. If I looked at someone's LER value and it read as 1.05, that tells me that between 0.04 above Pb+f and 90% paper D-max, the log exposure range of the paper was 1.05 and a negative with a density range of 1.05 will fit that paper nicely. Did doesn't tell me that the value was adjusted for flare. So, either I'm going to misinterpret the data or someone is going to have to include caveats along with the data. This is a problem I have with all systems. That's why I like to keep it as close to pure tone reproduction theory as possible.
Show of hands, how many people knew this was supposed to be part of the data when looking at BTZS testing results? How many people incorporate this factor into their BTZS testing?
Well there is that chapter on making a black hole for flare testing, so I knew BTZS tested for flare.
Whether he put it on the negative instead of in the camera quadrant where it belongs, that is a tricky question. Does flare belong on the camera, where it occurs - or on the film, where its effect becomes measurable?
So, presuming they are measuring the light intensity and range of the slide and the copy camera has no flare, it is essentially a no-flare setup. There is no link to any 'real scene' meter measurement, right? In that case their results (0.3 G) and the following standards based on those results (ASA and ISO) would primarily be valid only for film-plane exposure metering, right? Or is flare factored in somewhere in ISO or ASA?
Originally Posted by Stephen Benskin
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Absolutely! This is what I've been talking about. It's in the difference between the metered exposure, the speed point, and the shadow exposure. 0.10 Fb+b speed point is 1.0 log-H units below the metered exposure (Hg/Hm). The average shadow falls 1.3 log-H units below. Flare is what brings the shadows up around the speed point.
Originally Posted by ic-racer
Film speed would be a stop slower without flare, or a ~ stop slower EI if the technique doesn't account for it (Zone System).
The fractional gradient point for the ISO contrast parameters falls just about a stop below the 0.10 Fb+f speed point. This means that there is a one stop safety factor to account for variations in camera exposure, but also variations in flare.
Bill, it's not about whether BTZS recognizes the influence of flare. Davis' statement supports what I've been saying about the importance of incorporating the influence of flare into the interpretation of the data from a no flare test, and how it works with the negative density range and contrast determination (like with the Zone System).
Originally Posted by Bill Burk
My feeling is that from the almost off hand and generalized way he presents the concept in the book, it probably doesn't register with very many of his readers. I know this is the first time I can remember really noticing it.
I measured a few shots that I took last week where I checked Zone II and Zone VI.
Negatives measure 0.20-0.24 where I metered and placed on Zone II.
This is where I imagine Zone II belongs. So I consider the negative properly exposed.
Zone VI is 0.70-0.77 which across the exposure scale puts it where Zone V is supposed to be. Zone VI should be measuring 0.90.
I used EI 200 on the meter for TMY-2 (film developed to 320 at CI 0.58).
I am curious why my Zones landed where they did.
If flare allegedly gives a stop in the shadows. Why did I have to rate the film in half to place Zone II where it belongs? This is an open-ended question because I can always take more shots and note the meter readings and check where they land on film...
Could you attach the curve?
Here's the graph, Zone II and Zone VI are marked where they fell.