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Thread: Post flashing

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    cliveh's Avatar
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    Post flashing

    On a different forum, I read about pre and post flashing. I have never heard of post flashing. Can someone tell me when this technique should be used and the advantages it gives?

    “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

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    Would not not think there would be much difference either way. With prints post flashing works better for me for the simple reason that the neg has to be removed from the enlarger. I use the enlarger for the flashing light source . Do not think it would make a difference with negs ether.

    Mike

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    I don't really know if there's a difference in the result, but the idea is to raise the print's exposure threshold so that selected areas register immediately when there is an overall exposure. It just seems logical to me to do that first.
    John Voss

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    ROL
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    I thought post flashing was face saving vernacular for the unplanned result of accidentally turning on the lights before the print has been fixed, almost always in the presence of students.

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    Are you referring to film exposure or when printing?

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    Quote Originally Posted by Michael R 1974 View Post
    Are you referring to film exposure or when printing?
    Printing.

    “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

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    Usually when you flash paper, you give it just enough pre-exposure to non-image light so that the paper has been brought just to the threshold at which any further exposure will produce tone. The effect is to lower the contrast of the paper. It is therefore a technique of much more limited use with VC papers than with graded papers. With graded papers it could be used to get intermediate grades. And some people also used it so that they could use higher grades - which sometimes gave higher density blacks than lower grades (Richard Henry showed this effect with his meticulous tests of flashing with Ilfobrom).

    With VC papers, there isn't much point in flashing an entire sheet. However it can still be a useful technique for bringing in stubborn highlights if applied locally (and there are various methods of doing that). When done in this way the effect is essentially the same as burning in with a very low contrast filter.

    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.

    There are some threads here on flashing in the enlarging forum.

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    Good explanation of advantage of post flashing and technical advise how to do it given in the Ghislain Lootens book " Lootens on Photographic Enlarging and Print Quality"

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    Quote Originally Posted by Rudolf Karachun View Post
    Good explanation of advantage of post flashing and technical advise how to do it given in the Ghislain Lootens book " Lootens on Photographic Enlarging and Print Quality"
    Where Lootens used the term Flashing, he meant something quite different. He isn't talking about raising the exposure to a threshold to hold a delicate highlight. He wrote about a pictorial effect which he used to darken corners dramatically. He does mention all four times when you can flash paper; before, during or after enlarger exposure and also after print is in the developer - he cautions you about the risk of Solarizing (Sabbatier effect). He recommends flashing after enlarger exposure but doesn't explain.

    If I had to guess his reason to recommend flashing after exposing in the enlarger... I imagine you can have a clear short-term memory mental image of "where" the exposure has already happened, so a better chance of flashing the correct corners.

    I don't use flashing as a general rule. So, without experience, I can't add knowledge of whether "before, during or after" makes any difference. I am certain there is a sensitometrically-measurable difference. But I am guessing there is little difference visible on the print, and that the distinction exists to explain the way of working.

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    Bill, one relatively simple illustration of pre vs post non image exposure (note not necessarilly limited to below-threshold exposure but also fogging) is in Kodak's safelight test procedure. The procedure is designed to test the effect of safelight (ie non-image) exposure both before and after the enlarger exposure.

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