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Thread: Post flashing

  1. #21

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    Since the end result is the same as a pre-flash, and the pre-flash procedure is easier/more intuitive, I can't really envision a situation wherein one would post-flash...
    Hi, I'm just the opposite - I think post-flash is more intuitive. The way I do it is to first make a print (actually, test strips). When I get to where I'm happy, except for lacking a bit of highlight detail, I'll often try flashing. Typically I'll make another test strip, doing several flash exposure on it. I use a piece of cardboard over the print, same as I would for a print-exposure test, moving it in steps. So one test print might also get flashing tests of 1, 2, and 4 seconds. If the highlights are doing what I want, I can select a flash exposure or test further.

  2. #22

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    Quote Originally Posted by Mr Bill View Post
    Hi, I'm just the opposite - I think post-flash is more intuitive. The way I do it is to first make a print (actually, test strips). When I get to where I'm happy, except for lacking a bit of highlight detail, I'll often try flashing. Typically I'll make another test strip, doing several flash exposure on it. I use a piece of cardboard over the print, same as I would for a print-exposure test, moving it in steps. So one test print might also get flashing tests of 1, 2, and 4 seconds. If the highlights are doing what I want, I can select a flash exposure or test further.
    No argument from me if it works for you. I probably should have said pre-flashing is more intuitive to me. The results in the end should be the same.

  3. #23

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    Quote Originally Posted by Michael R 1974 View Post
    Actually I'm working on an article to show completely (including data) what flashing does (using MGIV), the differences between pre/post, and the effects of flashing at different grades. If there is interest on APUG I will post the article.
    It'd be great to see this article here.

  4. #24
    Bill Burk's Avatar
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    It'd be great to see the article.

    I hope you answer my burning questions: Is pre- vs post- just a way to distinguish the sub-threshold exposure from deliberate graying exposure? Does it matter if the total flash exposure occurs at any combination of before, during or after enlarger exposure? My gut tells me it doesn't matter and conventionally we do this because it is easier to figure out what amount of flash is desired by keeping the purposes separated in our heads.

  5. #25

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    I have similar questions, Bill. Still working on these tests and it will be a few weeks yet. Lots of data to go through. I've used localized and/or masked pre-flashing fairly often with extremely high contrast subjects, and always did it the way I was taught and the way it made most sense to me, but I've always wanted to do a rigorous "study" on it to hopefully answer some of the nagging questions I've had. Pre vs post is one of them, but the one I've had the most trouble getting my head around abstractly is what effect there might be (if any) if the flash exposure on VC paper is done with different filters. The conventional approach is to simply flash with white light, but I wanted to investigate this further. Another one of those rat holes I guess. The procedure works fine for me as-is, but who knows, maybe there are additional controls, or maybe a myth or two can be busted. There is little written about it, and no real evidence for any assertions. The exception is Henry's book - but that was with graded papers. So I kind of see this experiment as a continuation of his work but with VC papers.

  6. #26
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    Quote Originally Posted by Michael R 1974 View Post
    I have similar questions, Bill. Still working on these tests and it will be a few weeks yet. Lots of data to go through. I've used localized and/or masked pre-flashing fairly often with extremely high contrast subjects, and always did it the way I was taught and the way it made most sense to me, but I've always wanted to do a rigorous "study" on it to hopefully answer some of the nagging questions I've had. Pre vs post is one of them, but the one I've had the most trouble getting my head around abstractly is what effect there might be (if any) if the flash exposure on VC paper is done with different filters. The conventional approach is to simply flash with white light, but I wanted to investigate this further. Another one of those rat holes I guess. The procedure works fine for me as-is, but who knows, maybe there are additional controls, or maybe a myth or two can be busted. There is little written about it, and no real evidence for any assertions. The exception is Henry's book - but that was with graded papers. So I kind of see this experiment as a continuation of his work but with VC papers.
    Michael, with all due respect the tests you are trying to do including filter values, exploit so many variables that they become almost meaningless. From a physics point of view I find it difficult to believe that a pre-flash has the same effect as post flash. After exposure the latent image is at a variation of energy states across the entire shadow to highlight range. How can a post flash possibly give the same values as a pre-flash where the exposure value is zero and even before exposure to the variance of the image in question?

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  7. #27
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    The way I see it, Clive, is that if the amount of exposure thru the negative is x and the amount of flash is y, then x+y and y+x should yield the same amount of exposure. I do not think the silver cares when it is actually exposed first -- thru the neg or flashed without the neg.

    The idea of flashing is that the paper has a threshhold of z: the amount of exposure needed to get any tonal change beyond pure white. Flashing is used when x<z in the highlights where one wants some tone. In those areas you want x+y, or y+x, to be greater or equal to z.

    In the shadows, the exposure is on the order of 200x or greater (compared to x in the highlights). So 200x+y is not significantly different than 200x.

    Fun with x,y, and z!
    Last edited by Vaughn; 10-17-2013 at 05:34 PM. Click to view previous post history.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  8. #28
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    If I have one house brick next to another house brick and next to another house brick and I add 10 house bricks to each, they are all the same height (pre-flashing). However, if I put three house bricks one on top of one and 10 house bricks on top of the next and 30 house bricks one on top of the next and I then add 10 house bricks to each I have a variance of height (post flashing). Do you get my drift?

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  9. #29

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    Well the point of controlled tests by contacting calibrated wedges is to eliminate the variables, which enables one to answer questions like this.

    Clive, in your analogy see the bricks as units of light. In your "pre-flash" example you are adding 10 units of light to all the tones in your final print before the image exposure. In your "post flash" example you are adding 10 units of light to all tones in your final print after the image exposure. The variance of height is due to the image exposure.
    Last edited by Michael R 1974; 10-17-2013 at 07:31 PM. Click to view previous post history.

  10. #30
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    Quote Originally Posted by cliveh View Post
    If I have one house brick next to another house brick and next to another house brick and I add 10 house bricks to each, they are all the same height (pre-flashing). However, if I put three house bricks one on top of one and 10 house bricks on top of the next and 30 house bricks one on top of the next and I then add 10 house bricks to each I have a variance of height (post flashing). Do you get my drift?
    Isn't pre-flashing sort of like pre-visualisation?

    In a flood zone, I'd rather put them on the bottom. If I wanted a rooftop viewing deck I'd put them on top.

    Your second example sounds more like first burning, then flashing.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

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