Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,462   Posts: 1,570,643   Online: 822
      
Results 1 to 9 of 9
  1. #1
    Marco B's Avatar
    Join Date
    Jan 2005
    Location
    The Netherlands
    Shooter
    Multi Format
    Posts
    2,983
    Images
    169

    Reciprocity and contrast changes

    Hi all,

    Through some other thread here on APUG, I got to discover Ralph W. Lambrecht's DarkroomMagic website and some handy technical tools he has available under "Library":

    http://www.darkroomagic.com/

    Now this raised a question. I have been shooting quite a lot of nighttime photo's, often at extended exposure times where reciprocity kicks in. In the "Reciprocity compensation table" on Lambrecht's website, he not only shows some recommended compensation, but also a column with "theoretical contrast change". With values upwards of N+3 (that probably means a heightened / bigger contrast, does it?)

    I had never realized these were related... Dumb me probably probably, but anyway, does reciprocity failure indeed significantly change contrast, and are their people out there that do change their development practices accordingly? Any recommendations and info appreciated...

    Marco
    My website

  2. #2
    Jim Noel's Avatar
    Join Date
    Mar 2005
    Shooter
    Large Format
    Posts
    1,892
    Blog Entries
    1
    Yes, extended exposure definitely increases contrast. A sketchy explanation is the fact that bright areas record light immediately and continue to do so until the darker areas begin to record.

    If reciprocity charts indicate a need for up to N-1 the additional contrast is easily taken care of with variable contrast printing paper. If more than N-1 is indicated it is a good idea to follow those guidelines stated in the charts.
    [FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]

  3. #3
    Marco B's Avatar
    Join Date
    Jan 2005
    Location
    The Netherlands
    Shooter
    Multi Format
    Posts
    2,983
    Images
    169
    Thanks Jim,

    This helps a lot.

    Marco

  4. #4
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    In an article on testing reciprocity failure in Photo Techniques magazine in July/Aug 2003, Howard Bond found that modern films have less increase in contrast, and thus less need than older style films for reduced development with the long exposures required to correct for reciprocity failure. TMY and 100 Delta showed no increase in contrast at 4 minutes exposure, and Tri-X only a small increase. The Kodak recommended development reduction for Tri-X of 10%, 20%, or 30% at different extended exposure times didn't fit Bond's findings at all.

    I've also seen this reported elsewhere in a more anecdotal fashion, without such rigorous testing as Bond applied.

    So I think the best advice with modern emulsions is to test and/or critically examine your results as you work, and not necessarily take conventional wisdom based on older style emulsions as always valid with current films.

    Of course many night scenes (especially in cities with artificial lighting) tend to have a much greater dynamic range than typical daylight shooting, which might call for reduced development. But this isn't a case of reciprocity failure increasing effective contrast.

    Lee

  5. #5
    Marco B's Avatar
    Join Date
    Jan 2005
    Location
    The Netherlands
    Shooter
    Multi Format
    Posts
    2,983
    Images
    169
    In a way I agree with you Lee, as I haven't seen any real issues with most of my negatives. Actually, in a sense strive for some extra contrast and deep blacks in most of my night shots, so a small bit of extra contrast might not be a real problem.

  6. #6

    Join Date
    Sep 2002
    Location
    Willamette Valley, Oregon
    Shooter
    Medium Format
    Posts
    3,684
    Lately I've been shooting Acros for it's total lack
    failure out to 120 seconds. Some use the film rather
    than a faster due to it being effectively
    faster beyond 4 seconds. Dan

  7. #7

    Join Date
    Mar 2005
    Location
    Central NC
    Shooter
    4x5 Format
    Posts
    444
    Think of it like this. Reciprocity failure normally doesn't happen across the whole film at once. It happens in the shadow areas first.

    For example, say you are making a photograph of a stream flowing around rocks. Say it's a stream in the woods -- lots of shadows. So you end up with an exposure of 2 seconds or so. What happens here is the white water flowing around the rocks is properly exposed while the dark shadows caused by the rocks are in reciprocity failure and so are underexposed.

    You end up with some choices. You can expose for the shadows and develop normally only to find that your highlights are blown. You can expose for the shadows and use an N- contraction to pull the highlight density back down. Or you can expose for the highlights, develop normally, and let the shadows go black. Etc...

    But yes, reciprocity failure can be related to whole negative contrast increases because only part of the negative is seeing reciprocity failure while the rest is forming the latent image normally.

  8. #8
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    See "LIRF is Lurking at Tour F-Stop" at www.unblinkingeye.com by some kook named Gainer.
    Gadget Gainer

  9. #9
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    "Tour" should have been "Your" of course. Reminds me of the old story. A notice of a typo appeared in a newspaper:"In the last issue we referred to John Smith as a Defective in the police force. We should have said he is a Detective in the police farce." In our local newspaper, a story covering an overturning of a truck said it took a 1000 pound wench to right it. Quite a gal, that.
    Gadget Gainer



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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