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  1. #81
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    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?
    There are a whole slew of variables that come into play when testing and many of them aren't even considered by most people. Some of them that do, aren't really realistic. When it comes to flare, think about the camera image. You are taking a white card and stopping down. The characteristics of the camera image don't change. The camera image curve is just moved up or down with changes of exposure. There is no influence of flare by the time it gets to the higher tones, and that's with a scene with a normal luminance range.

    Another way to look at it is the ratio of the metered exposure to the speed point verses the ratio of the metered exposure to the average shadow exposure. With black and white, the ratio to the speed point is 10x or 1.0 logs. The ratio for the shadow exposure is 20x or 1.30 logs. The difference comes from flare. The ISO standard factors in around a stop flare. If camera testing incorporated flare then the majority of of the resulting film speeds resulting from stopping down 4 stops (1.20 logs) from the metered exposure would result in the ISO speed. But as most tend to fall 1/2 to 1 stop below, that suggests a mostly flare free testing environment.

    You can do the test that Bill suggests if you want to have an idea of how flare works, but as flare is variable not only with the luminance range but with the tonal distribution of the subject and lighting angle, it would be hard to apply the testing results to shooting. The best thing to do is to use the average value. Not only does it represent the results from the majority of situations, it is also the center of all possible outcomes which helps to minimize the degree of error.

  2. #82

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    What if the lens is wide open and I'm using shutter speeds to control exposure? Wouldn't flare from a brightly lit white card be in play even though I'm exposing for low values?

  3. #83
    Bill Burk's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    What if the lens is wide open and I'm using shutter speeds to control exposure? Wouldn't flare from a brightly lit white card be in play even though I'm exposing for low values?
    You have a really low contrast image at that point. Even if it is white, there's going to be less than a stop of subject brightness range. And assuming you are exposing at a fast shutter speed to measure low Zones, you are really underexposing the white (to make it almost black). Your flare is about four stops beneath that, barely causing an effect.

    Now if your camera had a light leak, that'll give you flare.

  4. #84
    CPorter's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    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.
    But what of the flare factor when enlarging? One stop? The image on the paper will be lower in contrast to some degree than the information on the negative, unless the negative is contact printed of course. If you assume a 1 stop flare factor, then an LER of 1.05 with consideration of one stop of enlarging flare, then a negative density range of 1.35 ( and higher CI) would help to offset losses from flare with enlargement, would it not?

  5. #85
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    What if the lens is wide open and I'm using shutter speeds to control exposure? Wouldn't flare from a brightly lit white card be in play even though I'm exposing for low values?
    In the conditions you've outlined, veiling flare would have to double the highlight exposure to reproduce the effect of one stop of flare, and I don't think it's capable of that. Take a look at the camera image curve. The white card falls at the high end. A one stop flare factor doubles the shadow exposure. An exposure of 0.0032 mcs is added each point on the curve. By the time it gets up to the highlight, it doesn't add much to it value. I would like to point out that this example uses a camera image curve representing a 71/3 stop average luminance range. A white card would be just a small line or a dot.

    In camera testing would meter the card and stop down. This just moves everything down.

    Click image for larger version. 

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    Just to help make a point, I doubled the amount of flare in the example below, and the highlight exposure almost hasn't changed.

    Click image for larger version. 

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    Here is the concept in a bigger context. The difference here is that it is based on testing using a middle gray card. It would be too messy to show the shift from a white card down to the shadow exposure.

    Click image for larger version. 

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    Last edited by Stephen Benskin; 02-14-2012 at 07:55 PM. Click to view previous post history.

  6. #86
    Bill Burk's Avatar
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    Quote Originally Posted by CPorter View Post
    But what of the flare factor when enlarging? One stop? The image on the paper will be lower in contrast to some degree than the information on the negative, unless the negative is contact printed of course. If you assume a 1 stop flare factor, then an LER of 1.05 with consideration of one stop of enlarging flare, then a negative density range of 1.35 ( and higher CI) would help to offset losses from flare with enlargement, would it not?
    You might be onto something there. But be careful, I wouldn't want you to overdevelop on account of some theory we haven't hashed out yet.

    I use a filed negative carrier that exacerbates flare at the enlarger by letting additional white light spill around the edge.

    And I have a negative that I call my "upper control limit" that has "important" densities that range 1.18 and when I print, it barely fits Grade 2. The neg has overall range 1.61 which includes spectral highlights, but I don't count that.

    So I aim to keep my negatives no higher than 1.18 - not a far cry from 1.35 but still I want to go no higher.

  7. #87
    Stephen Benskin's Avatar
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    I'm kind of in the middle of something, but I want to throw this out there. It is Annex A: Relation between the paper range (R) and the effective density range of the negative from ANSI/ISO 6846 - 1983 for photography (sensitometry) black-and-white continuous-tone papers - determination of ISO speed and range for printing. The second paragraph should sound familiar, but it's the third paragraph that has much of the answer. The first, second, and forth give the reason why talking absolutes with the NDR / LER relationship is impossible.

    "The log exposure range of a photographic paper provides a useful, but not a perfect, criterion for grading papers. It is useful because a satisfactory print is normally obtained when the log exposure range of a paper is matched to the effective density range of the negative image, provided that the scene and the scene lighting are normal. It is not a perfect criterion because papers with similar log exposure ranges will give prints that differ considerably in appearance if the shapes of the paper sensitometric curves are different. Moreover, a negative which prints well on a glossy paper (high Dmax) will print equally well on a matte paper coated with the same emulsion (low Dmax) even though their log exposure ranges will not be the same.

    ISO range (R) which is determined directly from the log exposure range is, therefore, a useful guide for selecting a paper for a negative of known density scale. What is involved is the matching of the ISO range (R) with 100 times the effective density range of the negative image. For medium contrast papers, an exact match generally works best. For low contrast papers, the LER should be slightly less than the negative density range in most cases and conversely for high contrast papers. This means that to obtain the best prints from a single negative using two papers which differ in Dmax it is necessary in most cases for the lower Dmax, (lower contrast) paper to have a smaller LER.

    When a negative is contact-printed, its effective density range image equals its diffuse density range as measured by a properly calibrated transmission densitometer (see ISO 5). When an enlarger is employed, the effective negative density range will be greater because of the scattering characteristic (Q-factor) of the negative film, (Stray light [flare] typically reduces the density scale by 5 to 10 %). A direct determination of the effective density range of the negative can be made with a photometer by measuring the maximum and minimum illuminance of the projected sharp image on the enlarger easel.

    It must also be remembered that optimum print quality depends on aesthetic factors which may indicate the use of a paper whose log exposure range differs considerably from the density range of the negative. Thus, the use of the ISO range/negative density range relationship is only approximate, as a starting point for critical work. The paper range required should be determined for each printed/enlarger, developer, and paper surface combination."

  8. #88
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    [QUOTE=Bill Burk;1302658]
    You might be onto something there. But be careful, I wouldn't want you to overdevelop on account of some theory we haven't hashed out yet.
    I already develop to a NDR of 1.2 and I'm certainly not overdeveloping. Using ZS vernacular, that's a range between a Zone VIII target density for "normal" development of 1.3 down to the EI threshhold of 0.1 at Zone I. IMO, I don't think it's useful to discuss a range on the negative that exceeds the upper limit of the textural range i.e., Zone VIII, perhaps to Zone IX, which I do not consider specular in nature...............or, a range that falls below the threshhold. Referencing Stephen's post #87, I consider the "minimum" illuminance to be the threshhold point at Zone I and the "maximum" illuminance to be, probably a Zone IX illuminance, but I currently have completed tests using Zone VIII as the important upper limit of the density range.

  9. #89
    Bill Burk's Avatar
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    [QUOTE=CPorter;1302701]
    Quote Originally Posted by Bill Burk View Post

    I already develop to a NDR of 1.2 and I'm certainly not overdeveloping. Using ZS vernacular, that's a range between a Zone VIII target density for "normal" development of 1.3 down to the EI threshhold of 0.1 at Zone I.
    Does this print on Grade 2 (or the equivalent filtration) for you or do you have to go to Grade 1? Anyway I just don't want you to change to 1.35 based on this discussion if you already found 1.2 works.

    I was going to carry my tests through to the end and draw a chart of my 4-quadrant tone reproduction before deciding my desired target range. Then I found that real negative that "proved" what my target range should be, and short-circuited my plan to carry my tests to the conclusion.

    After all, I had my answer.

  10. #90
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    [QUOTE=Bill Burk;1302853]
    Quote Originally Posted by CPorter View Post

    Does this print on Grade 2 (or the equivalent filtration) for you or do you have to go to Grade 1? Anyway I just don't want you to change to 1.35 based on this discussion if you already found 1.2 works.
    The short answer is, yes. I base that on just how easily I can produce a very satisfactory "straight print", no dodging or burning or other measures. In the way of an explanation, that is, a decided upon enlarging exposure time that fulfills my expectations (visualization if you will), both in the high value tonal area(s) of the print in the regions of Zone VII and VIII and the low value area where I made the particular shadow "placement". If I can achieve that, then I know I have something I can work toward within the confines of the information in the negative for the print I saw when the exposure was made. For me, I don't find any glory in making a satisfactory final print from a difficult and fussy negative, I find it annoying and who wants to be annoyed while in the darkroom .

    I realize that some of the wordage here is somewhat cliche', especially for anyone who is fluent with the ZS, but being cliche' in no way diminishes the method.
    Last edited by CPorter; 02-15-2012 at 06:12 PM. Click to view previous post history.

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