Paper Theory

Discussion in 'Darkroom Developing and Printing' started by Rex the Strange, Aug 2, 2005.

  1. Hello All,

    Another question for those who know something. I have some 8x10 photo
    paper that I'm not entirely happy with the results of. I've been
    exposing it at F22 (that's the third lowest F-Stop for my enlarger) for
    15 seconds and I get nice blacks and grey tones. However, whites are
    not white. The problem seems to be that the paper doesn't have a lot of
    contrast - or - I'm not exploiting it.

    My understanding is that, for example, F22 at 10 seconds produces the
    same amount of light as F16 for 5 seconds or the next lowest F-Stop
    (which isn't marked on my enlarger) for 20 seconds.

    So here's the question: does any of this affect the contrast of the
    image? Can I get better contrast by, say, using a brighter light (read
    as: lower F-Stop) for less time or is it entirely up to the paper and I
    just have to accept the fact that my paper sucks?

    tia
    rts
     
    Rex the Strange, Aug 2, 2005
    #1
    1. Advertisements

  2. Rex the Strange

    Mike Guest

    Your chosen aperture (f-stop) on the enlarger lens makes absolutely no
    difference in contrast.

    You need more contrast if you aren't getting bright whites. Assuming you
    are using variable-contrast paper, add magenta filtration. Or develop
    your film longer
     
    Mike, Aug 2, 2005
    #2
    1. Advertisements

  3. Thanks MIke. I was afraid of that. How about adjusting the developer
    chemistry?

    rts
     
    Rex the Strange, Aug 2, 2005
    #3
  4. Hello Strange One!

    There's a good chance that your paper is being fogged. I'd suggest
    that you cut a small piece of paper from a sheet in the dark (no
    safe lights), and fix it completely in the dark. If it isn't white,
    it has been fogged (perhaps old or heat damaged) or the fixer is
    nearly dead.

    If it passes the test, repeat the procedure in the dark, but develop the
    unexposed section before fixing it. If the developer is contaminated
    with agents that fog the paper, it should be evident.

    If it's still white, take another small section, place it on the easel,
    and cover half of it with an opaque paper pack or film box. Cover the
    lens with a lens cap, and expose for your 15 sec @ f/22. If the enlarger
    doesn't leak light, you shouldn't see the paper during the exposure.
    Develop and fix in the dark to see if the enlarger fogs. You can do
    similar test with "pre-exposure" or perhaps, expose 1/2 the sheet with
    the cap for 1 min, then remove the cap and the mask covering 1/2 of the
    paper, and expose a negative. If there's enlarger fogging, 1/2 the print
    will be darker and more fogged than the other side.

    Also, test for exposure from safe lights. Do a Google groups search to
    find detailed explanations of the approach.
     
    Michael Gudzinowicz, Aug 2, 2005
    #4
  5. I tested the paper by processing a blank sheet. It passed the test and
    came out perfectly white.
     
    Rex the Strange, Aug 2, 2005
    #5
  6. Rex the Strange

    dan.c.quinn Guest

    You processed a blank sheet. How did you test the
    blank sheet; on the easel with, as suggested, the
    enlarger turned on?
    I've an enlarger lens which projects the image
    and with that a disk of light. The disk projected
    beyond the image and likely included the image area.
    That lens was soon on the shelf. Some fault in the
    mechanics of the lens? I recall thinking, What
    the Hell's going on; a light leak through
    the lens itself? Well I never. Dan
     
    dan.c.quinn, Aug 2, 2005
    #6
  7. message
    You are right in general about time vs: f/stop for
    exposure. Paper does have reciprocity failure the same as
    film but this does not have a significant effect on exposure
    over a rather wide range, say 1 second to one minute. Most
    papers have published reciprocity curves.
    Reciprocity failure, if its happening, results in the
    exposure being lower than expected but should not affect
    contrast, I think you have another problem.
    If the highlights are grayed down I would check your
    safelights using the method in the Kodak publication K-4
    (available from the Kodak web site). Also, check your
    darkroom for leak light. Turn off all light and give your
    eyes ten or fifteen minutes to become completely dark
    adapted.
    Paper contrast can affect highlights if the negatives are
    too low in contrast and you print for normal shadow density.
    Check the negatives. In the absense of a densitometer the
    rule of thumb is to lay the negative on a sheet of printed
    paper and see if you can read the print through the
    highlights. Kodak recommends that for diffusion printing the
    density of the brightest highlights _that are to have some
    detail_, like the forehead highlight in a portrait, should
    just obscure the print. For a condenser enlarger the print
    should be just readable through the highlight.
    Choose print contrast visually. You may have to make
    several tests. Whatever contrast you are using now try going
    up one grade. If that doesn't look right go up another
    grade.
    Too long development can also cause some highlight
    veiling. Depending on the paper and developer most RC papers
    are fully developed at between one and two minutes. Fiber
    papers generally need more time, probably about two minutes
    average. For most papers and developers development beyond
    about four minutes will begin to cause fog problems. While
    paper development time _can_ compensate for small exposure
    errors the range is not much.
    Note that you may get slight highlight veiling during
    normal enlaging that does not show up if the paper is simply
    fixed out in the safelight. The effect of the exposure makes
    a difference, this is accounted for in the Kodak method.
    Ilford has a somewhat different but equally effective test
    on their web site.
     
    Richard Knoppow, Aug 2, 2005
    #7
  8. The reason I processed a blank sheet was to determine whether the paper
    had latent fogging and was, therefore, trashed. It wasn't. Seems the
    paper is okay. The suggestion that the fogging is caused by some sort
    of light leak seems unlikely as none of my other papers are affected.
    I'm now beginning to suspect that it's just a highly reactive paper and
    that I just need to lessen the exposure.

    Thanks all for the suggestions. I'll keep you posted on what goes on.
     
    Rex the Strange, Aug 3, 2005
    #8
  9. Rex the Strange

    gr Guest

    The f-22 is probably a contributing factor. It will produce considerably
    lower resolution than f-11 or f-16. A good enlarger lens is probably
    optimum at 2 stops down from wide open, a lesser lens 3 stops down. If
    you have misalignments and curvature of the negative to contend with,
    maybe f-16 will still work for you. (btw: diffraction is what is causing
    the lens to limit resolution).
    gr
     
    gr, Aug 15, 2005
    #9
  10. A good enlarger lens should perform well regardless of the f/stop.
    With a good enlarger lens and proper alignment you or lets say the
    average print maker probably won't see a difference between a print made
    at f/ 5.6 and f/45. F/stops on enlargers should be thought of as a means
    to control light, not as a method of sharpening prints from semi sharp
    negatives or negatives that are not flat.
     
    Gregory Blank, Aug 15, 2005
    #10
  11. Rex the Strange

    gr Guest

    I was referring to the fact that lenses suffer from diffraction limited
    resolution which varies with the physical size of the aperture. For a
    given effective f-no (this would be the same as the marked f-no at
    infinity and higher as you increase mag toward 1:1 then higher yet into
    actual magnifications) the resolution is limited for a perfect lens.
    Real lenses have lower resolution yet, but very good lenses are close,
    especially in the central zone. For example, with green light the
    maximum resolution a lens can produce at f/2.8 is 536 c/mm. At f/5.6 it
    is 268 c/mm. At f/11 it is 136 c/mm. At f/22 it is 68c/mm and at f/45 it
    is 33c/mm. In an enlarger the limiting c/mm is actually much worse
    because the lens is used at a magnification and the effective f/# is
    much higher than marked. For a good 6 element (and some 4 element)
    lenses, 2 stops down from wide open is probably the best setting. If the
    lens has a bit of flare and aberrations, 3 stops down is probably best.
     
    gr, Aug 21, 2005
    #11
  12. Then again like I said, next to no one will ever notice unless the lens
    is really bad at whatever f/stop is chosen.
     
    Gregory Blank, Aug 24, 2005
    #12
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.