I don't think it works that way with subject flare, where the high lumincances affect the lower ones. I think the characteristic curve under those conditions is basically a "given" (ie we cannot control the flare), and increasing or reducing exposure simply moves the subject range up and down that curve. So reducing the exposure would result in more compression because more of the subject values fall on the flattened portion of the curve.
Originally Posted by Michael R 1974
One of the reasons why using the prefixes CI and ISO means the testing adhered to a methodology.
Last edited by Stephen Benskin; 01-28-2013 at 03:17 PM. Click to view previous post history.
Keep in mind that flare doesn't change the film's toe... it only affects the light falling on the film plane.
Originally Posted by Michael R 1974
This is an example situation where you can see "more clearly" what's happening because you separated your flare tests from your film tests.
So the flare light provides enough light to lift you off the toe. There is compression, but it's compression of the light bringing you shadow tones to the film. Nothing you can do about that (except maybe a compendium hood) but try to keep the lowest of the shadow tones on the straight line portion of the film.
But since flare lifted you up off the toe, you can still reduce your exposure and remain above the toe.
You guys are running away leaving me behind.
What I gather rather expose more to reduce flair instead of decreasing exposure. Which I think is better anyway if the light permits.
Otherwise if one decreases exposure one should extend development by an "X" amount to have a general compensation for the resulting flatness.
You do some disagree?
Bill, I've been wanting to touch on this and even thought about doing it in a new thread. I need to put together a couple of illustrations.
Originally Posted by Bill Burk
In the mean time, here is a chart showing the values off of my four quadrant curves. The top set of numbers are from a no flare situation. The bottom from a one stop flare. Both exposures place the Zone I exposure on 0.10 over Fb+f. Flare has doubled the shadow exposure from 0.0041 to 0.0082. The value of 0.0041 is added to each step. At Zone VIII, it doesn't even make a dent. Flare has also reduced the 8 Zone range down to 7. The 1.14 non flare NDR becomes 0.98 with flare. The paper grades are adjusted to match the NDRs and LERs. The Q4 reproduction curve gradients show how the local contrast is affected.
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It's already been established that flare is "high luminances affecting low luminances" and that there are two types "veiling" and "ghost" (or polygonal flare)-----and, that it does not exist unless there is a lens to deliver it to the film. The flare that I may try to counteract is certainly not "ghost" flare, but the veiling kind that is going to raise density in the low zones where I don't want it. This is not unlike pre-exposure to the film that does the same thing, add density to the low zones, but with pre-exposure, it is purposeful and desired. So, reducing exposure, will reduce exposure to all subject luminances equally, I could not use the term "compression" to describe the result of reducing exposure. Too much reduction, obviously, can push important negative detail clean off the curve, but I fail to see, at the moment, where any compression of values occurs at all.
Originally Posted by Michael R 1974
Last edited by CPorter; 01-28-2013 at 09:53 PM. Click to view previous post history.
Reason: I left "veiling" out in the 2nd sentence.
So, am I wrong in thinking that flare is a generalized, like pre-flashing.
Mark Barendt, Beaverton, OR
"We do not see things the way they are. We see things the way we are." Anaïs Nin
Well, I don't think so. I like to equate it to pre-exposure to film, however---but I generalize it completely, perhaps even marginalize it, but I don't totally dismiss it. IMO, aparently, there's volumes that can be discussed in the theory, but it's relegated to much less discussion when it comes to actually photographing. That's not a jab at the discussion, it's just how I feel about it.
Originally Posted by markbarendt
Henry's book shows the effects of flare on the film's characteristic curve. This has long been the standard approach (up until computers became common); however, it doesn't represent how flare really works. It's a construct for the sake of simplification and easier than drawing a separate flare / camera image curve.
The one thing this type of graph does very effectively show is the reduced gradient caused by flare. Still, my belief is that the film's characteristic curve is a graphic depiction of how the film responds to exposure under specified processing conditions. An exposure of a given log-H will always fall at the same point on the curve. What the Henry curve does is to take what the density would be at Zone II 1/2 and places it on Zone I. But what really happens is flare moves the Zone I exposure to the right along the X-axis and it becomes the exposure where Zone II 1/2 would be in a non-flare situation.
The above graph is how one stop of flare works. The shape of the film curve doesn't change, the optical image is what has changed in relation to the original image. This is why it's important to have no flare testing (if curve plotting is involved). As flare has little effect on the higher exposure values, the placement of the highlight exposure doesn't move. With the shift in the placement of the shadow exposure, the effective scene luminance range has shortened by one stop from a range of 2.20 to 1.90 (statistically normal flare is generally calculated at 0.34 to 0.40 reducing the illuminance range to 1.86 to 1.80). Normal processing would then be for a 6 1/3 stop range and not the original scene's 7 1/3 stop range.
The reason why most people don't have to worry about film with exposure is because it is built in (and as explained in the last paragraph). Without the effects of flare, the shadow exposure would fall approximately one stop further to the left. Flare moves the shadow exposure back up. The ISO film speed standard tests under no flare conditions, but factors in flare. For a 125 speed film, log-H at speed point should equal 0.0064 lxs.
Published processing times also have flare factored in. Kodak's normal CI is 0.58. A statistically average scene has a luminance range of 2.20. The average grade 2 LER aim for a diffusion enlarger is 1.05. Based on the rise over run equation, these two stats would produce a CI of 0.48. If flare reduces the apparent luminance range by 0.40 making it 1.80, the resulting CI would be 0.58. So if you follow the instructions, you don't need to worry about normal flare.
Now the amount of flare tends to change with changes in luminance range. How this is handled can require some attention, but other factors can contribute to make any extra effort unnecessary. I like to keep the following graph in mind.
This shows the density ranges of negatives, that were judged to produce prints with excellent print quality, superimposed over the paper curve which they were printed on. Notice the diversity of NDRs. They all produced great prints. How precise does anyone actually have to be? Could this be the reason why good images are made regardless of the approach? The way I see it. Aim for the center. Even with all the potential variables and variances, you'll still hit the target.
Last edited by Stephen Benskin; 01-29-2013 at 12:25 AM. Click to view previous post history.
Originally Posted by AndreasT
It's OK... High flare situations are not going to be flat so you don't extend development. There will be bright lights and dark shadows.
Old rule of thumb for amateurs is to expose more in high flare situations like backlighting and silhouette. That's only because of bad metering.
ChuckP is talking about metering carefully and then, because the shadows aren't as black as he wants, making them a little blacker.