Newbie: Use of Contrast Filters and Exposure Time

Discussion in 'Darkroom Developing and Printing' started by KS, Aug 20, 2004.

  1. KS

    KS Guest

    I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
    should I be adding time to my exposure? Thx.
    KS, Aug 20, 2004
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  2. Very definitely. Kodak has a darkroom handbook with a wheel for
    calculating how much more time.

    Francis A. Miniter
    Francis A. Miniter, Aug 20, 2004
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  3. KS

    dr bob Guest

    There are variations in the way VC paper reacts to contrast filters.
    Usually as the filter No. increases (from yellow towards blue) additional
    exposure is required. The exact amount in stops or time can be calculated
    by various methods, but I find a trial and error approach using small paper
    pieces a much quicker path to the desired result. E.g., cut (or tear) an
    8x10 sheet of the target paper into rough quarters. Place one in a
    conspicuous area of the image and expose. It usually requires no more than
    two trials to acquire sufficient data for a full size print. Remember: the
    first full size print is still just a "working" print. You will usually
    want (need) to tweak the print in many ways before satisfaction is achieved.

    Truly, dr bob.
    dr bob, Aug 21, 2004
  4. KS

    KS Guest

    I actually found the instructions for my Kodak Polycontrast II Filter Kit.
    It says no exposure adjustments from 0-3.5 and then double the exposure when
    using 4-5.5. Go figure. To quote: " Each half grade step changes the
    log-exposure range of Kodak papers approximately 0.1 units. Filter 2 is
    intended to accommodate a negative density range of 1.2 in a typical
    semi-specular enlarger with tungsten lamp..."
    KS, Aug 22, 2004
  5. KS

    Phil Glaser Guest

    I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
    The Variable Contrast Printing Manual by Steve Anchell outlines an
    entire procedure for materrials testing to determine the degree of
    exposure change when going from one contrast filter to another.

    Although I know about these methods for testing, so far I've been
    getting along using Ilford's (Multigrade IV) chart, according to which
    the paper speed is constant up to filter 4, at which point it drops by
    one stop (requiring a doubling of exposure). My sense is that this
    approach is ok for me, for now, because Ilford's test were with a
    tungsten light source (as mine is) and because I'm using Ilford's
    standard Multigrade developer. I'm still seeing how consistently the
    paper speed remains constant between filters, but so far it seems ok.
    Ultimately I will do these tests, especially as I get into different
    developers and papers. (As it is, I'm trying to balance my obsession
    for technical precision with my aspiration to understand form and
    compisition, and so I'm skimping on the paper testing for now.)

    Also, one thing I do is to _always_ start with _a_ filter. For me # 2
    seems to be the right one (bearing in mind that # 2 is not necessarily
    the equivalent of grade 2; again, see Anchell for details). My
    experience is that the absence of any filter with VC paper gives a
    result that is, well, undefined: I'm just not sure what's going on.

    Bear in mind that there are lots of variations that can affect the
    tests and your outcomes in general. Public enemy number 1 in this
    department is voltage fluctuations. See this discussion thread for
    further details:


    Phil Glaser, Aug 22, 2004
  6. KS

    dr bob Guest

    True. And Ilford instructions are similar. However, I have experienced
    slight and somewhat more than slight differences in exposure when moving
    from one filter situation to another. IOW, "correction" of the contrast for
    one gray level _may_ create the need to modify the overall exposure in order
    to maintain a desired level in another. So far my approach is to be more
    empirical than less. Tests work well.

    Truly, dr bob.
    dr bob, Aug 23, 2004
  7. I was stunned when I went to photo school and experienced changing contrast
    settings (via dial) on an enlarger made for the purpose - no time changes
    after a desired exposure was made at any contrast!

    At home, on the other hand, I use a contrast filter under the enlarger lens.
    I think any change in contrast is worth running a new test strip. By the
    way, I am printing on Ilford multigrade IV using Kodak filters. I have been
    assured that the Ilford and Kodak filters are completely interchangable.
    Pieter Litchfield, Aug 23, 2004
  8. KS

    Mike King Guest

    First of all, both Kodak and Ilford claim that the lower grade filters are
    "speed matched" in other words no time compensation is required when
    changing filter grades, and I suppose that's true for one particular point
    on the gray scale but in the real world we change filters to change the gray
    scale so a retest of exposure is often necessary.

    Second, the claim that Ilford and Kodak filters are completely
    interchangable is also not quite true, you will often get different results
    when switching from one brand of filters to the other and may not be able to
    obtain the complete contrast grade range of a variable contrast paper unless
    using filters from the same maker. That being said, most of the time most
    of your work will not be made with either the highest or lowest contrast
    available and will be perfectly satisfactory using brand X paper with brand
    Y filters.
    Mike King, Aug 25, 2004
  9. KS

    Bob Salomon Guest


    This is a function of some MG heads. Others may require different times
    at different settings. The Kaiser MG head is one example of one that has
    constant time at any grade (unless you dial in the ND filter control on
    the head).

    However it is always best to run a test before printing to make sure you
    are happy with the changed contrast, as well as to see if the time
    should be increased or decreased for the effect you want.
    Bob Salomon, Aug 25, 2004
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