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  1. #11
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    BTZS teaches how to shoot a "black hole". It's a large-ish cardboard box spraypainted black inside with a shade like a lens shade over an opening cut in the front. You put this in your pictures, like a prop, and shoot away. The theory is it is pure black. No light that goes in comes out. So any density over base+fog on the
    I did a test like that some years ago while working on an article about flare and the film speed. The set-up consisted of the black box and four cards, white, grey, black, and mixed, with holes cut out of the middle to go over the black box opening.

    I based the exposure on a grey card. I then made exposures of the four different set-ups. Being me, I then exposed a sensitometric strip to run with the black box test. I read the density from the area of the box opening and placed the density on the film curve.
    Attached Thumbnails Attached Thumbnails Flare target comparisons.jpg  

  2. #12
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    Quote Originally Posted by Stephen Benskin View Post
    I did a test like that some years ago while working on an article about flare and the film speed. The set-up consisted of the black box and four cards, white, grey, black, and mixed, with holes cut out of the middle to go over the black box opening.

    I based the exposure on a grey card. I then made exposures of the four different set-ups. Being me, I then exposed a sensitometric strip to run with the black box test. I read the density from the area of the box opening and placed the density on the film curve.
    So the light reflected off the target bounced around the lens and contaminated the black box area kinda like my doorway to Chimayo messed with my metering.

    This is one of the creative uses I was hoping to see in this thread.

    Like pre-exposure, I assume this particular type of flare would actually help get the shadow areas up off the toe a bit more.

    Is that a fair thought?
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  3. #13
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    So the light reflected off the target bounced around the lens and contaminated the black box area kinda like my doorway to Chimayo messed with my metering.

    Like pre-exposure, I assume this particular type of flare would actually help get the shadow areas up off the toe a bit more.

    Is that a fair thought?
    In general 80% of flare comes from the subject which leaves only 20% coming from stray light. In the black box example, flare added 0.38 more log-H exposure with the white card compared to the black.

    Flare works exactly like pre-exposure. That would be a good way to look at it.

    If you look at the two quad example, you'll notice the camera image has two curves. One is a non flare curve and the other is a one stop flare curve. Look where the non flare curve intersects the film curve. Without flare, film would be one stop slower. The ISO film standard factors in one stop of flare into the speed calculation. So, you should assume that you will always have around a stop of flare in most average shooting situations. Higher flare will add more exposure to the shadows effectively making your film faster. A good rule of thumb is 1/3 stop more or less flare per stop increase or decrease in subject luminance range.

    Down side of flare is the compression of the shadows.
    Attached Thumbnails Attached Thumbnails 2 Quad flare example.jpg  

  4. #14
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Mark,

    You seem to be jumping around a bit on what type of flare you're interested in. I have a feeling this isn't it, but I put together graphs of 3 examples of camera image flare to compare: no flare. one stop flare, two stops flare.
    Well yeah.

    So what, this is a creative/artistic/practical use question.

    If can I look at a scene and put together a good idea of whether or not to use my lens hood, based on the subjects and lighting, and if I want those subjects closer or farther from each other on the curve that's huge.

    I'm actually thinking that not having a hood on when I shot at Chimayo may actually have been a blessing. If the flare caused the the shadows, the people inside and the alter, to get off the toe and land on the film a zone closer to the highlight exposure, the people near the door and the building facade; that's actually better for me when I get to the enlarger.

    Actually you bring up a great thought with regard to types of flare, I don't know what they all are/might be and I don't know what can be done to mimic flare either. That's shy in the op I suggested that the second pyro bath might mimic pre-exposure/flare, in essence reducing overall contrast.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  5. #15
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Down side of flare is the compression of the shadows.
    Yeah and part of what I'm looking for is knowing how to place exposure to account for that.

    If I'm going to use flare to reduce contrast, then I need to know what my limits are to be able to meter well.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  6. #16
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    Yeah and part of what I'm looking for is knowing how to place exposure to account for that.
    Flare makes it impossible to determine where the shadow exposure will fall. If you look at the very bottom of film curve in the two quad example, you'll see a Delta X notation. That point indicates the fractional gradient speed point (found using the Delta-X Criterion). The fractional gradient point is the minimum point of exposure that will produce an excellent print (determined from the Loyd Jones First Excellent Print testing).

    Even if it was possible to shoot a scene and experience zero flare, the exposure will still fall at a point where an excellent print is still possible. This also means that there is about a stop safety factor built into the film speed standard.

    As flare varies considerably depending on the tonal distribution of the scene, the idea of film speed and proper exposure is about finding a placement that allows for the variance without sacrificing quality. There's a misconception with some that there are specific densities for specific "Zones." According to Jones, negative density isn't an important factor in the determination of print quality. The critical factor is gradient.

    You've probably seen this graph before, but this is an good time to review it. It shows the relationship between the negative exposure and the perception of quality in the finished print. Point A is the First Excellent Print which has it's exposure at the fractional gradient point.
    Attached Thumbnails Attached Thumbnails first excellent print.jpg  

  7. #17
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Flare makes it impossible to determine where the shadow exposure will fall.
    I think Mark and I are going to be satisfied with "rule of thumb" and "at least the right direction" kind of estimates.

  8. #18
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    I think Mark and I are going to be satisfied with "rule of thumb" and "at least the right direction" kind of estimates.
    That's what I'm saying. Rule of thumb is all there is. You can't be certain where the shadow exposure will fall because of flare.

  9. #19
    markbarendt's Avatar
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    You guys must work the night shift.

    Stephan, Bill's right in that I'm not looking for an absolute measurement, your card/black box experiment actually gives me the tool I need to figure this out in general.

    I can see that in the situation I had at Chimayo I should have expected; 1-flare to trick my N90s's meter into thinking the scene was brighter, and 2- flare to lower the overall contrast of the film as a pre-flash would do.

    With those two expectations I could looked at the scene and known to add "some" exposure knowing that flare was probably tricking the meter and knowing that it was a mixed scene, compared to your card test, I would have known to add "some" exposure to "refill" the paper's curve because of the reduction in contrast flare was going to provide.

    As a side note, this also reinforces my preference for incident metering.

  10. #20
    Stephen Benskin's Avatar
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    Mark, I'm glad the information was useful.

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