another question re film grain

Discussion in 'Darkroom Developing and Printing' started by Noons, Jul 15, 2007.

  1. Noons

    Noons Guest

    I've recently started using b/wfilm again.
    More specifically, delta400 and xp2.
    Last time I used b/w was >25 years ago,
    so my memory of it is nothing but foggy!
    I'm currently scannning the film with a 9000ED.

    One thing I've noticed: the grain in both of these
    films seems to be proportional to the exposure:
    in dark sections or just plain underexposed, the grain
    is quite visible. In light areas or slightly overexposed
    images, it reduces significantly.

    Is there a rule/guideline/theory for this?
    Somewhere I can read about it?

    TIA for any ideas.
    Noons, Jul 15, 2007
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  2. Graininess, that is the appearance of grain, depends on
    many things. The actual silver or dye particals which make
    up the image are microscopic. In emulsion research they are
    usually examined wtih an electron microscope although a high
    power optical microscope will resolve them. What is seen as
    grain is the "clumping" of grains at various levels in the
    emulsion. Since the distribution of grains is random the
    effect is to combine into larger groups of grains which are
    also random. On prints the grain is actually from clear
    areas in the negative where the grain clumps allow light to
    Graininess does vary with density. Usually visual
    graininess is minimum at medium density and is more
    noticable at low and high density. This may be what you are
    seeing. Also, if you are getting grain on scanned negatives
    but don't seen it visually it may be a sort of aliasing due
    to a complex interference pattern between the grain and the
    scanning pattern of the scanner.
    Note that some think that dye image films, whether color
    of monochrome, have no grain. In fact they have the grain of
    the silver image which generated the dye in development.
    However, because the dye is in very small particals and
    forms in "clouds" around the original silver, it may be less
    noticable. This applies to the XP-2 which is a "chromogenic"
    film, that is, the image is composed of dye particals rather
    than metallic silver.
    Grain and graniness (percieved grain) has been
    researched pretty thoroughly and articles can be found in
    some of the older textbooks on photography. Kodak also had a
    booklet on grain and graininess which may still be on their
    web site. While this applies to color films it may still be
    helpful. Search for E-58.
    As a rule, at least for B&W silver image films, exposure
    should be minimised to that which will result in adequate
    shadow detail. This tends to minimise grain and maximise
    sharpness. For formats larger than 35mm, where minimum grain
    and good avoiding image spread is less important somewhat
    more exposure may result in better tone rendition.
    The ISO speeds for B&W still negative film reflect the
    minimum exposure for good shadow detail. Color films and
    other types of films are measured using a different standard
    aimed for most films at best tone rendition.
    Richard Knoppow, Jul 16, 2007
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  3. There are a couple of points I left out:-( One is that
    the size of the silver grains varies with the speed of the
    grain. Although emulsion making technology over the years
    has resulted in much finer grain for a given speed its still
    true that faster emulsions are grainier than slower ones and
    that the faster halide grains in the emulsion result in
    larger silver grains. This tends to work against the idea
    that the dense areas have more grain because that is where
    the silver from the least sensitive halide grains is
    concentrated. However, again, visible grain is not from the
    silver itself but from statistical groups of grains.
    Another point I should make is that I refered to grain
    "clumping" from statistical distribution of grains in the
    emulsion, this is correct but there is another kind of
    clumping. This is actual physical clumping due to migration
    of silver particals toward each other in emulsions that have
    been softened. This is one reason highly alkaline developer
    like Rodinal tend to produce larger grain than lower pH
    developers like D-76. The effect is much less pronounced in
    modern films because they have very hard emulsions that do
    not swell much in processing. The other kind of clumping is
    due to the distribution of grains in the emulsion and is not
    affected by swelling or developer pH.
    Richard Knoppow, Jul 16, 2007
  4. Noons

    Noons Guest

    Thank a zillion, Richard. That answered all my questions
    perfectly. I'll chase up the doco as well. Yes, I'm aware
    of the scanner alias "grain" problem as well. It's
    particularly noticeable with older films such as D400 with the
    "hazy" emulsion side. FWIW: I've noticed it is much reduced
    with newer colour neg films such as the latest from
    Fuji and Kodak: these have an emulsion side that is much
    less "rough" and show almost no scanner alias grain
    with scanners like the 9000. The latest batches of Kodak
    chromogenic BW film - BW400CN - also don't show this problem
    as much as Ilford's.
    Noons, Jul 16, 2007
  5. Noons

    darkroommike Guest

    When we first went hybrid at my paper, shoot film then scan
    for prepress, we found that negatives that looked too thin
    to print scanned well and scanned faster on our Leaf scanner
    that did "normal" negatives.
    darkroommike, Jul 17, 2007
  6. Noons

    UC Guest

    Yes, in my book.

    Briefly, the thinnest areas of the negative are hit by the least
    light. Every emuslion contains a variety of grain sizes. The smaller
    ones are the least sensitive. The largest ones are the most sensitive.
    Larger ones have a statistically higher probability of being struck by
    light. The lower the light intensity, the greater the proportion of
    large grains that are exposed. Thus, shadows contain a higher
    proportion of exposed and developed large grains than mid-tones or
    UC, Jul 24, 2007
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