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Thread: Post flashing

  1. #11
    Bill Burk's Avatar
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    I was trying to find that safelight test illustration because, yes, it clearly shows the degradation that an unsafe "safelight" can cause.

    So I went to Google... and it led me back to myself on APUG... "The Kodak test was a still-life Siamese cat sculpture with polished silver pots".

    Now WHERE did I see those cats?

  2. #12
    Bill Burk's Avatar
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    Found 'em. Kodak Filters for Scientific and Technical Uses, Kodak Publication No. B-3 - Page 51.

    Doesn't show whether exposure before or after makes a difference. But the side which had "prolonged" exposure to safelight (the proper safelight filter with the proper bulb at the proper distance... but for too long)... was clearly degraded.

  3. #13
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    Funny this topic coming up now. I use pre-flashing for my paper negatives to help control contrast a little and increase speed. I learned about it by reading Joe VanCleave's notes over at f295.org but I know he's posted his method here at APUG as well.

    Like here:
    http://www.apug.org/forums/forum62/6...eflashing.html

    I make a test strip for each paper type, and pick the exposure that is 1 second shorter than the faintest visible tone in good light after dry-down. Joe uses graded paper but I use VC paper and only preflash through a green filter, so I'm differentially pre-flashing the low contrast emulsion.

    The reason this post was timely is that recently I've made a number of paper negatives using post flashing instead. This was due to being in a hurry or wanting to reload a one-shot camera while a paper was developing and not wanting to turn on my enlarger during that time. Using exactly the same enlarger height/aperture and filters, for exactly the same amount of time that I use for pre-flashing, I am unable to see any difference. So in my context, post-flashing can be more convenient... pull the paper out of the camera, stick it under the enlarger for 17 seconds ( or whatever for the paper type ) start my pre-soak and load the camera with a fresh sheet of paper. I'm almost sure I remember Joe saying that post-flashing was almost the same as pre-flashing, but not exactly the same. But in practical terms, my experience says I can use them interchangeably. Whatever the difference is, it's too small to matter for my mostly pinhole photos. I also use paper in lensed cameras, and have post-flashed a few of those in the past few months too, with equally acceptable results.

    I have never used pre or post-flashing during printing, so I can't comment on that at all.

  4. #14

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    Quote Originally Posted by Bill Burk View Post
    Found 'em. Kodak Filters for Scientific and Technical Uses, Kodak Publication No. B-3 - Page 51.

    Doesn't show whether exposure before or after makes a difference. But the side which had "prolonged" exposure to safelight (the proper safelight filter with the proper bulb at the proper distance... but for too long)... was clearly degraded.
    Bill, when all else fails you can always go back to my "article" with the Kodak and Ilford resource links (shameless plug). Here it is under publication K-4:

    http://www.kodak.com/global/en/consu...Safelite.shtml

    The point I was making is that the test is intended to show the effects of the same amounts of non-image exposure both before and after the image exposure (analogous to pre and post flashing).

  5. #15
    Bill Burk's Avatar
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    Ah, you mean this Article?

    http://www.apug.org/forums/forum37/114562-ilford-kodak-resources.html

    You are right, it illustrates the difference between pre- and post- flashing. In the diagrams shown, Pre-flashing appears to affect the entire scale, while Post-flashing appears to affect the toe (highlights). The diagram is not an actual photograph, as it is in Publication B-3, but the kitties and kitchenware photo doesn't show pre-flashing.

  6. #16

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    Les McLean, formerly of this parish, describes both pre and post flashing with illustrations in articles on his website and in his book Creative Black and White Photography - worth purchasing if you don't have a copy.

    pentaxuser

  7. #17
    cliveh's Avatar
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    I may have got this wrong, but surely pre-flashing softens the paper contrast and raises the inertia of exposure level. However, is not post flashing a form of uniform fog of the paper already exposed to the negative? As at this point the exposure has gone beyond threshold.

    “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

  8. #18
    NedL's Avatar
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    Quote Originally Posted by cliveh View Post
    I may have got this wrong, but surely pre-flashing softens the paper contrast and raises the inertia of exposure level. However, is not post flashing a form of uniform fog of the paper already exposed to the negative? As at this point the exposure has gone beyond threshold.
    Clive, with my paper negatives, I'm exposing them as if they had been pre-flashed. So the total exposure to all light is the same either way. I don't think this is analogous to post-flashing while making an enlarged print, unless the print is intentionally underexposed before flashing...

    I'm curious about this too... I'll check out Les McLean's site.

  9. #19
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    I haven't tried post-flashing, but pre-flashing makes a HUGE difference when pushing the crap out of films.

    My example is with colour film, Superia 800 exposed at 12800.

    FTR, my pre-flash method was double exposure, I held a tissue over the lens and metered through that with camera meter, and determined the pre-flash amount. It was with a Canon AE-1, I used that 'trick' of winding tight the left hand spool and holding it, while pressing the rewind button then gently advancing the frame advance lever.

    C-41 @ 6 minutes.

    12800 no pre-flash

    Superia 800 @ 12800 no preflash by athiril, on Flickr

    12800 with 'zone 3' pre-flash (Zones 1 and 2 did nothing essentially, all of a sudden at this point density suddenly jumped up, contrast improved, shadow detail increased).


    Superia 800 @ 12800 Zone 3 preflash by athiril, on Flickr
    Last edited by Athiril; 10-15-2013 at 08:05 PM. Click to view previous post history.

  10. #20

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    Quote Originally Posted by cliveh View Post
    I may have got this wrong, but surely pre-flashing softens the paper contrast and raises the inertia of exposure level. However, is not post flashing a form of uniform fog of the paper already exposed to the negative? As at this point the exposure has gone beyond threshold.
    Yes pre-flashing (or post-flashing) lowers paper contrast. Both pre and post-flashing can put uniform fog on the paper if done incorrectly (or if that is the intent - which it occasionally is). Perhaps what you're missing here is the procedure. Assume you want to pre-flash. You first do a test strip using non-image light and find the longest exposure time that does not result in any print density/fog. That is your pre-flash exposure. Then you incorporate the pre-flash into all further test/work prints. Since you're determining your image exposure with paper that has been pre-flashed, the pre-flash exposure is taken into account when you find your print exposure. So there is no unwanted fog.

    Post-flashing is harder because you have to work backwards, first determining the maximum amount of image exposure that yields no highlight density, then finding the amount of post-flash required to just bring in the highlight detail from the image exposure. If done correctly the end result would be the same as the pre-flash (although the flash exposure time might not be the same). 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, unless it is part of a broader sequence of masked exposures.

    Bottom line is that wherever you flash, you lower paper contrast. So in general it is a much less useful technique with VC papers than with graded papers.
    Last edited by Michael R 1974; 10-15-2013 at 08:50 PM. Click to view previous post history. Reason: tried to be clearer

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