Reducing enlarger exposure.

Discussion in 'Darkroom Equipment' started by fidget, Dec 4, 2006.

  1. fidget

    fidget Member

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    This is a newbie question, I guess.
    If I want to increase my enlarger exposure time so that I have more time to burn and dodge etc, aside from reducing the aperture (which might have other effects) is there a combination of colour dial up settings which will do this, but which won't effect the contrast setting (which may have been set on the dials)?
    I wondered if was as simple as adding the same amount of colour on each dial to what was already set for the grade that I was working on.

    Regards, Dave......
     
  2. Dave Miller

    Dave Miller Member

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    Hi Dave, you are correct; equal amounts of each filter will act as neutral density. Don't be afraid to stop the lens right down though. If you do a few test prints, same print at different aperture and compare, this wiil soon tell you if there is a problem with your lens.
     
  3. Mick Fagan

    Mick Fagan Subscriber

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    Dave, generally speaking, adding 30 units of all three colours, will add one stop of density.

    In practice this means that if you are exposing at 10 seconds for a correct exposure, adding 30 units of each colour should make the correct exposure 20 seconds, or very close to that.

    You can, if you have enough filtration left, add extra units of equal filtration to get more time for fiddling with the print.

    Mick.
     
  4. Jon Shiu

    Jon Shiu Subscriber

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    Hi, what would the effect be of just adding cyan? (The ND filter on my LPL VCCE looks like cyan to me.)

    Jon
     
  5. avandesande

    avandesande Member

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    At first I thought this thread was about somebody who wanted to make postcards out of their 11x14 negatives...
     
  6. Mick Fagan

    Mick Fagan Subscriber

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    Jon, ND filters on enlargers are a neutral grey, or should be, they just add density to the light source.

    Adding only Cyan will add density, but change the colour of the light because the Magenta and Yellow filtration will have their effect diluted by the Cyan, the net effect will be a lowering of contrast. This is not the effect being requested.

    The effect of adding all three colours to lengthen the exposure, works for colour and B&W equally.

    Mick.
     
  7. Justin Cormack

    Justin Cormack Member

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    So did I. How do you do that? Always been quite curious.
     
  8. crispinuk

    crispinuk Member

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    You use an Ensmaller :rolleyes:
     
  9. srs5694

    srs5694 Member

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    In theory, adding cyan filtration does nothing but remove red light from the mix; blue and green light are unaffected. Because most B&W papers are insensitive to red light, the effect should be nothing (or close to it, given that the paper's red-insensitivity is imperfect). That said, I don't know how "tight" most cyan filters are -- if they actually block even a small amount of blue and/or green light, they'll have some effect on contrast. Thus, it could be that in practice what you're saying is true for some or all subtractive enlargers.

    On a practical note, but one that probably won't be useful to fidget, I've got a Philips PCS130 with a PCS150 control module/light source. This is an additive color enlarger -- it's got separate red, green, and blue channels rather than cyan, magenta, and yellow filters. I've done some tests with this enlarger, and I found that completely turning off the red light has no effect on my B&W prints. Exposing using the blue and green lights alone produces prints that are indistinguishable from what I get with all three lights. This is theoretically equivalent to dialing in maximum cyan on a subtractive enlarger -- but keep my above caveat in mind. Also, and more to the original point, adjusting the green and blue lights' brightness by equal amounts affects exposure. The lights are calibrated in Kodak color filtration values, and adjusting both the green and the blue by 30 units changes exposure by one stop (doubling or halving exposure time or changing the lens's aperture by one stop). If your enlarger is calibrated in the same way, the same adjustments should work for you, or at least be close.

    All of this applies to B&W VC printing. For color printing, an adjustment of all three filter values is necessary to adjust exposure. In theory, increasing the filter values by 30 will effect a 1-stop change in exposure with no change in final print color. In practice, if the filter calibration is off or if the filters "leak" light outside of their claimed color ranges, there may be a slight color shift when you make such an adjustment. With my Philips, I'm able to make such changes with no change in color. (At least, when the changes are small; I generally only tweak it by a 10-30 units to get the exposure time I want.)