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  1. #1

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    Ilfochrome/Cibachrome printing

    I'm going to try ilfochrome printing for the first time tomorrow. I'll be printing 4x5 Velvia onto 8x10 paper, using fresh P30 chemistry and fresh paper. I have access to a colour enlarger head and a Jobo processor.

    I've been thinking I can get a feel for contrast and exposure times by contact printing 4 negatives onto a sheet. Due to the costs involved I'd like to get it right first time and be able to translate those numbers into numbers I can use for a real enlargement.

    I don't know much about printing, but I'm reasonably good with maths and physics. Presumably the inverse square law comes into effect here and I simply need to adjust my exposure times to the square of the factor of which I move the enlarger head?
    Does a 10 second exposure at 20cm becomes a 40 second exposure at 40cm?

    Any other hints/tips? I've done a bit of B&W work before, so I roughly know my way around. Unfortunately, I don't personally know anyone who prints colour so I will need to teach myself from books and forums.

  2. #2

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    You can get close by using the inverse square law for printing. However, I find that it works best when changing between two enlargements, rather than when moving from a contact sheet to an enlargement. I would just test strip a sheet once you put the film in the carrier, with starting times extrapolated from the contact sheet you just made.

    BTW, you mean "contact printing four transparencies onto a sheet", don't you?
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  3. #3

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    Quote Originally Posted by 2F/2F View Post
    You can get close by using the inverse square law for printing.
    Why only close? Reciprocity failure?
    Last edited by Martin Lee; 08-10-2009 at 06:29 PM. Click to view previous post history.

  4. #4
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    Just an idea, if you had a scale reference on your slide (e.g. an overlaid graticule or homemade scale) that gets enlarged and projected along with the slide, then you could compute the enlargement factor very accurately.
    "Only dead fish follow the stream"

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  5. #5

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    Quote Originally Posted by 2F/2F View Post
    BTW, you mean "contact printing four transparencies onto a sheet", don't you?
    I do! Sorry, force of habit, film = negatives in my head... I'll try to break that one.

  6. #6

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    If you set the enlarger head at the height for doing a full frame 8x10 from your 4x5 transparency when you do the contact sheet, you won't need any exposure adjustment.

  7. #7

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    Theoretically, I would think that what bdial sez is true. However, in practice, I usually get differences in exposure when doing it (and definitely a difference in contrast). Perhaps the light hitting the film first and then heading toward the paper versus the light heading toward the film and paper on the same plane fall off in slightly different ways.

    To make it easier on myself, I always make an initial test strip or test print, and then use it to make more fine adjustments. I do consider the enlarger settings from the contact sheet to decide how to step the test strip, though I will usually stop down a stop or so to give myself tighter increments.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  8. #8

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    Better to choose easy-to-print transparencies at first. Ilfochrome is pretty easy but only if you start with good exposures that have a dynamic range of 3.5 to no more than 4 stops. Beyond that and it can get ugly, without unsharp silver masking or some elaborate dodging and burning. Velvia can be difficult due to the overamped saturation added to the enhanced Ilfochrome saturation. Velvia transparencies shot on overcast days in light that looks a little flat--often punch up nicely. But don't judge Ilfochrome color balance or density until the prints are completely dry!

    Even with perfect transparencies, you're going to waste some paper and chemistry due to not knowing the basic set up for the specific enlarger lamp incl color filtration. It changes slightly with different emulsions and different packs of paper. Inverse square works, but it'll be easiest to mention that a contact print with the enlarger rail set to 8x10 will require the same exposure as the 8x10 itself, at the same f/stop (provided, If you don't move the rail too much in focusing later). From there to an 11x14 is a skosh more than a stop lost. When you get much beyond 60 seconds reciprocity failure starts to get logarithmic. For this reason I found it easiest to standardize on a time of 48 to 60 seconds, at a middle aperture like f/8 where sharpness is best without diffraction. Changes to dichroic filtration also adds density. I found that a Jobo Colorstar functioned pretty well as not only an enlarging timer a simple spot and area densitometer (that controlled the enlarging timer) was sometimes very useful to help calculate exposures when switching enlargement sizes or when making and adding unsharp masks.

    Your best bet when starting out is to fastidiously keep a log of EVERY darkroom exposure, noting every variable for every enlargement.

  9. #9

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    Do not vary time, but vary lens aperture. Color papers have reciprocity failures more severe than black & white.

    4 4x5 contacted should require the same time a projected 8x10 less a little for contact glass light blockage, say 5%. a 16x20 will be 2 stops more than 8x10.

    If you reuse developer or partially reuse it like 1/2 new and 1/2 old, things also go off.

    Most glass is colored somewhat, usually green, so you also need to take that into consideration if you get magenta prints

  10. #10

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    Success! Somewhat. I have made some prints. Some have mistakes, some don't.

    I'll go for a round two some time this week, probably Thursday and then write up what I've learnt as a newbie, which hopefully should be informative for anybody else starting out.

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