Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,302   Posts: 1,536,186   Online: 652
      
Results 1 to 9 of 9
  1. #1
    cdowell's Avatar
    Join Date
    Dec 2009
    Location
    Durham, N.C.
    Shooter
    Medium Format
    Posts
    112
    Images
    28

    Does preflash dissipate over time?

    Potentially a dumb question, but I feel like I've read that somewhere. I'm wondering if I can pre-flash lots of paper for use as paper negatives and then use it weeks or months later. Or does the energy dissipate over time, if not pushed over the threshold into actual chemical change/gray tones? Thanks.

  2. #2
    Bob Carnie's Avatar
    Join Date
    Apr 2004
    Location
    Toronto-Ontario
    Shooter
    Med. Format RF
    Posts
    4,651
    Images
    14
    Wow thats a good question, I think the big brains need to jump on this one,

    I would think that flash/fog would be permanent lots of paper like Fuji Metallic have a heavier Dmin that give it character and I think this is exactly how it would be done.

    I will be interested to see the answers on this one.
    Quote Originally Posted by cdowell View Post
    Potentially a dumb question, but I feel like I've read that somewhere. I'm wondering if I can pre-flash lots of paper for use as paper negatives and then use it weeks or months later. Or does the energy dissipate over time, if not pushed over the threshold into actual chemical change/gray tones? Thanks.

  3. #3

    Join Date
    May 2005
    Location
    Daventry, Northamptonshire, England
    Shooter
    35mm
    Posts
    6,936
    From what I have read here and elsewhere it does dissipate over a relatively short time like a few days only and wouldn't last weeks or months. There are probably several threads on this. Do a search. Someone is almost bound to have mentioned how long pre-flashing remains.

    pentaxuser

  4. #4

    Join Date
    Dec 2010
    Shooter
    Medium Format
    Posts
    188
    The short answer is that it can. The latent image is not always stable and can fade. However, you need to run test to find out the stability of the latent image. For film it is a larger problem as people keep their film in the camera a long time and so much research has gone into improving the stability of the latent image. Paper is more likely to be developed after exposure so it is not a very big concern for paper emulsion designers.

  5. #5
    Bob Carnie's Avatar
    Join Date
    Apr 2004
    Location
    Toronto-Ontario
    Shooter
    Med. Format RF
    Posts
    4,651
    Images
    14
    Thinking of this a bit more.. Metallic colour paper is grey where it should be white, therefore I assume they have pre flashed, from time of manufacture to time of usage it could be months if not years. therefore I believe the OP will be ok pre flashing, for film I cannot say.
    Ron M would be the go to guy to answer this one IMO

  6. #6

    Join Date
    Sep 2006
    Shooter
    35mm
    Posts
    38
    How about post-flashing? I do that with paper negatives in my pinhole camera to good effect. Sometimes during development the shadows aren't registering, so I give it another pop.

  7. #7
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Preflashing and reciprocity failure both fall under the heading of latent image keeping and both deal with low energy exposure and time. Immediately after exposure silver atoms that will develop may give off electrons and convert back to silver halide. This happens proportionally more in the shadows where there are lower exposure levels. Most of the loss happens in the first few seconds after exposure and tends to plateau off after a few hours. This is the reason there is a hold time between exposure and processing in the ISO standard for testing for film speed.

    It's probably best to test if you are planning on doing preflashing. Then be consistent with you hold time if you are using a short preflash to exposure ratio.
    Last edited by Stephen Benskin; 01-29-2011 at 03:45 PM. Click to view previous post history.

  8. #8

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    3,773
    In books that mention preflashing and describe the technique it is always done just before the actual print exposure.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  9. #9

    Join Date
    Feb 2007
    Location
    VT
    Shooter
    Multi Format
    Posts
    574
    Images
    1
    I've been wondering about paper negatives from a pinhole camera- can they be processed a week after exposure without trouble?



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin