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  1. #1
    David Ruby's Avatar
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    This is going to show my lack of knowledge right off the bat, but could someone explain, or point me to a good book about how to deal with changing exposure times when changing filters with VC paper?

    I seem to remember reading about a chart possibly that you could use after you've determined the proper base exposer and then wanted to change the contrast with filters. Do different filters have a factor that you add or subtract to maintain the proper exposure?

    Would anyone recommend the Kodak darkroom dataguide? If so, anyone know a good place to look for one at a decent price?

    Thanks.

  2. #2

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    My understanding is that until you get up to the higher grades exposure stays constant. This assumes you first figured out exposure with the #2 filter in place. Which paper are you using? I know the Agfa datasheet claims that up to grade 4 it's constant. 4 and above it looks like you lose a stop. From looking at it I'm guessing in reality what they've done is put some ND into the lower filters so they print the same across the range. Grade 2 without a filter is much faster then grade 2 with a filter.

  3. #3
    ann
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    Some papers (not Kodak) will have a data sheet with the paper that will give
    you that information. Generally speaking the rule of thumb is that from 00 to 3.5 will be the same time ; with 4 up needing a 100% increase as the paper speed decreases in half.
    The small print also says "must test for personal results". Or something along those lines. Take that to heart.
    With some, the times will vary from grade to grade before reaching 3.5
    The paper defaults to grade 2 without a filter, however, make a print a grade 2 filter and then one without and they do not look alike.
    In our lab we recommend that students increase exposure about 50% when moving up from grade 3.5 to 4 and above as that works better with the paper, developer and water content in our lab.

  4. #4
    David Ruby's Avatar
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    thank you. i'm using Kodak polycontrast now, that's probably why I didn't see anything in the box. I'll experiment a bit.

  5. #5
    Black Dog's Avatar
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    Try Steve Anchell's Variable Contrast Printing Manual. Also useful info in mags like View Camera, Photo Techniques etc.
    "He took to writing poetry and visiting the elves: and though many shook their heads and touched their foreheads and said 'Poor old Baggins!' and though few believed any of his tales, he remained very happy till the end of his days, and those were extraordinarily long "- JRR Tolkien, ' The Hobbit '.

  6. #6

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    If you're using a dichro head the usual rules of thumb for VC heads don't quite match. With my Durst M605 color head I find it necessary to make exposure adjustments with as little a change as from neutral or Grade 2 to either Grade 2.5-3 or 1-1.5.

    This could be due to the condition of my filters or personal preferences (I tend to print dark) but in my experience with this enlarger and Ilford and Agfa variable contrast, multigrade, whatever, papers, the transition from neutral to either direction via magenta/yellow filters is not linear.

    Being a lazy bum I haven't bothered implementing the various techniques published on the web to accomodate these differences. I simply make new test strips in quarter stops when changing a full grade or more and go from there.
    Three degrees of separation from Kevin Bacon.

  7. #7
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    There are all kinds of methods of dealing with the exposure variations due to filtration, many dependent on the producer of the products involved. I have not seen any universal method of compensation that work well yet. I always have had to make strip tests.

    There is another issue here. As the contrast changes, the overall exposure usually has to be “corrected” because every “zone” will be rendered differently. This may be the primary reason no one has been able to produce the
    ”universal correction” chart or formulae (equations). I love this stuff ;-)

    dr bob
    "I love the smell of fixer in the morning. It smells like - creativity!"

  8. #8
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    it is supposedly possible to adjust the contrast with a color head without changing the time by using more than one color so that the overall density of the filters does not change, just the color. But I've personally never tried this as it also increases the exposure time.
    Let's see what I've got in the magic trash can for Mateo!

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  9. #9
    Ole
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    I've been through this, and given up. I now use an Ilford EM10 enlarging meter: Regardless of contrast and filtering, putting nearly-white on 80 on the meter gives an exposure time of 10 seconds on Ilford Multigrade. I adjust aperture and filtering until the reading is right, not the other way round.
    -- Ole Tjugen, Luddite Elitist
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  10. #10
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