Pre-exposing film for decreased contrast ?

Discussion in 'Large Format' started by doug_mcfarland, Jan 28, 2001.

  1. For the most part I shoot primarily in heavily wooded areas, often in bright sunlight with deep shadows. I prefer to create images with bright open shadows, so I am constantly fighting against high contrast. Up until now I have been primarily concentrating on film compensation development and latent image bleaching to help create the images I seek.

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    However, over the years I’ve read about, but not tried, the technique of pre-exposing sheet film prior to field exposure, presumably to decrease overall contrast of the film (AA “The Negative” p119-123). I’m not excited at the thought of discovering yet another way of destroying film, I already have quite a few successful methods already :)

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    So I am interested in hearing from anyone that uses this technique, your successes or failures, or any tips you might have that would help me.

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    TIA - doug
     
  2. It works fine. The basic idea is that if Zone II has 2 units of light
    and Zone VII has 64 units of light, a uniform 'fogging' exposure of 2
    units will add 2 units right across the scale. The difference is that
    Zone II gets elevated to Zone III (2 units from scene plus 2 units
    from fogging exposure) but Zone VII hardly shifts at all (64 + 2 =66
    units).

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    The fogging exposure can be made before or after the main exposure
    (so, if you can keep your film seeparate in the field, you can always
    add the extra exposure in your darkroom). You can use either your
    enlarger or a pre-exposure device which is essentially like a
    diffusor or you can fill the frame with a grey card and expose it to
    the grey card. Essentially, what you end up with is a deformation of
    the characteristic curve by lengthening the toe. You get similar
    deformations of the curve from flare.

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    The downside is that you lose local contrast in the shadows. That is,
    you hold a longer scaled subject but the local contrast in the
    shadows decreases (since lengthening the toe basically reduces the
    slope of the toe part of the curve). I guess its an individual
    aesthetic decision as to when you would use it. I would suggest this
    as a tool to use when you need to hold a longer scale but local
    contrast in the highlights is crucial.

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    Your goal of open, luminous shadows suggeests this is an area of
    crucial local contrast. However, a lot depends on how you visualize
    it. Shadows can be open and luminous but soft, which suggests a
    reasonable placement (fairly high on the toe) and something like a
    fogging exposure. Or they can be open and luminous but quite hard, in
    which case it could be a fairly high placement (to move the shadows
    off the toe) and compensating development.

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    Hope this helps. DJ
     
  3. How about giving a compensating development process like
    split D-23 a try. I too shoot in high contrast situations and this
    developer allows me to read my shadows, place them around
    zone 4 and still not block up the highlights.
     
  4. Why not try the same thing but with your print. Flashing the paper to
    bring it up to the exposure threshold is easy to do. Just experiment
    with the exposrue times to get the level of detail in the highlights
    and then print for the standard time. Paper is alot less expensive to
    work with than film. Alot faster, too. Thats my two cents.
     
  5. Polaroid used to send a diffuser with a close-up attacment kit no.583.
    You could probably find one for almost nothing on ebay if you're the
    adventurous type. It is a white plastic diffuser with 3 little ears
    that, as luck would have it, will cling to a 67mm filter. In those
    situations you're referring to, if I remember which is the hardest
    part, I put the diffuser over the front of the lens and adjust the
    aperture to expose for zone II. Then take it off and resume the pic
    with my normal exposure. For starters try doing it both ways on the
    some pic in the same film holder to see if you like the difference. 1
    as normal, and 1 with the diffusion fog added.
     
  6. As I noted in my lengthy question, I’m using a lot of techniques
    after the film has been developed. I use graded paper and use general
    overall flashing quite often, more recently latent image bleaching,
    and also compensating film development. I used to use D23 but didn’t
    like the overall results. Now I process in PMKpyro which is not
    recommended for compensating development, but I’m experimenting with
    a new technique for development (err should I say destroying film :)

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    I hadn’t considered post-exposure film flashing. Since I usually
    shoot two plates, I could develop one and then consider the alternate
    plate for pre-development exposure.

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    thanks - doug
     
  7. It makes no difference whether you preflash or post flash your film.
    The poster who suggested flashing your paper makes a point, BUT, the
    downside is you have to test the paper with a series of flashes (while
    taking notes) in the darkroom to determine correct exposure. With
    film, you know the speed, and if you've made a light reading, you know
    exactly how many stops to close the lens down to reach a zone II
    exposure. Moreover (this is the important bit), flashing PAPER is
    helful to tame PAPER contrast, not FILM contrast. In other words,
    flashing the paper will not give you shadow detail that is not
    ALREADY recorded on the film. If you want to record additional shadow
    density on film, then flash the film, or it's pointless. The advantage
    to this is two-fold: you "get it in the negative," which means you
    don't have to flash every damned piece of paper from here to eternity,
    and you've got a negative with a long tonal range, which can be
    suitably printed on various grades of paper for different contrast
    renditions. The best, best, best, friend to the photographer, with
    regard to this issue, is Ansel Adams' book "The Negative." If you
    consider yourself a photographer, you should have it on your shelf. .
    it will obviate several trips to photo.net for what is sometimes
    conflicting advice:))) Also, Adams is ALWAYS right on technical
    issues, so you can be assured that if you follow his advice, you will
    have mastered your technique.
     
  8. IMPORTANT!!!!!!
    I forgot the most obvious thing!!!!! Flashing the paper increases
    HIGHLIGHT DENSITY in the print, not shadow!!!!! Flashing paper in the
    darkroom will have no effect on your shadows at all (remember we are
    dealing with a negative tone process here), so my original point on
    film flashing stands.
    For notable examples of what flashing can do, watch "Evita" (only one
    example). The DP flashed the film with several warm shades of yellow,
    which gave the effect of filling in the shadows with warmth and body
    to match the South American evening light he was shooting in.
     
  9. Thanks for the notes Josh - I didn't think about the long term
    advantage of having a better shadowed negative as opposed to always
    fighting with contrasty negative printing-after-printing.

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    Also you mentioned AA's book "The Negative" - I referenced that in my
    original question - I'm never without it, and a 1/2 dozen other high
    quality books as well :)

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    I also like the suggestion of a field diffuser that would clip to the
    lens.

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    I knew this forum was a good place to post this sort of question.

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    Thanks Doug
     
  10. Regardless of whether you can see much difference in the negatives,
    there is a big difference between pre and post exposure. Pre-exposure
    brings the film up onto the curve already, basically getting ready
    for exposure in dim areas without them being off the bottom of the
    scale. It might be thought of as "presensitizing" instead. What would
    have been too low to record is now exposed at a level on the curve
    where it can be captured. Post exposure will do nothing to move the
    original subjects higher on the scale when they are exposed. They may
    fall too low and will not register, then you add blank density over
    that. Why? The idea is not just to fog the film, it is to make it
    more receptive to what light there is available. However, when you
    have to print through the fog, there may not be much of difference,
    so it may appear similar. They idea is different, though.
     
  11. With regard to pre versus post exposure, there is no difference, in
    senitometric terms, between flashing before or after the main
    exposure. Presensitizing or hypersensitizing is another technique
    altogether wherein you bake the film in a gas (usually a combination
    of hydrogen and nitrogen) to increase its sensitivity. A related
    technique, often referred to as latensification i.e., latent image
    intensification, involves making the least developable grains hit by
    light developable. This is done after exposure but before development
    by exposure to peroxide (if I remember correctly).

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    As far as flashing goes, there is no difference whether the flash
    comes before or after the main exposure. What matters is the total
    quantum of light that hits individual areas of the negative and the
    'fogging' flash basically will increase the responsiveness of the
    grains to the main image light by overcoming some of their inertia
    i.e., by moving them up to the toe point in the curve. This happens
    even if the flash occurs after the main exposure ie.., the main
    exposure records parts of the image on the curve and parts below in
    proportion to light refelcted from the scene. Additional light serves
    to move all of them up the curve. This can be tested by
    exposing two photographic papers or films to a step wedge, one with a
    flash before and one with a flash after. There should be no
    difference in fog densitiy and density of each step. Cheers, DJ.
     
  12. Here's a place that sells a nice diffuser to use for this purpose:

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    http://www.expodisc.com/
     
  13. WAn

    WAn

    An illustration how a pre-exposure modifies the film curve, assuming the initial film curve (in black) was a straight line with contrast=0.5:
    [​IMG]
    The values in brackets show the amount of pre-exposure.
    Regards, Andrey
     

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