Densitometer Question

Discussion in 'Darkroom Equipment' started by CPorter, Mar 17, 2007.

  1. CPorter

    CPorter Member

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    Need some input from the experts. I have access to densitometer at a local photo store and the man says I can use it to read my negatives anytime I want. But he says he has only used it for color film and he does not know if it will be accurate on black and white film. My question is does it have to be a certain densitometer to read black and white film or will any densitometer do.

    Thanks,
    Chuck
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    All of the ones I have used have an R/G/B/W setting. Red, Green, Blue and White light.

    When set on W, the densitometer can read a color neutral patch or a B&W patch.

    If this is missing, then the unit cannot read B&W.

    PE
     
  3. Helen B

    Helen B Member

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    It depends on whether you have silver-only images, or pyro-like stained image. If you have silver-only negs then a colour densitometer will work. Most channels should read about the same (maybe small differences in base density because of its colour), but there's no harm in using the blue channel for normal enlarging paper. The 'visual' channel is usually filtered to match the photopic (bright) spectral response of the eye, so it is green-ish.

    There may be a choice between Status A and Status M for the colour channels. Status A is intended for materials that are for viewing (eg slides, motion picture prints) and Status M is meant to mimic colour material sensitivity, and it is used for negatives, interpositives, internegatives etc - stuff that isn't viewed. For B&W work it probably won't matter which blue channel you use, but it might as well be A.

    If you have negs with an imagewise stain it will be more important to try to match the channel you use to read the density to the spectral sensitivity of the next step - so again the blue channel will be fine for graded paper.

    I suggest that you give it a go, and see how much difference, or lack of difference, there is between the available channels. Find out how to calibrate it as well.

    If you find out which densitometer it is, I'm sure that someone here will be familiar with it.

    Best,
    Helen
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    Well, I'll add to Helen's post that the W setting has no 'status' as it has white light, and the UV quantity in most units is filtered out so any UV component is missing from the light.

    There is also Status "D" used for reflection print materials that should be added to the list. Either A or D can be used for prints, but D is preferred.

    PE
     
  5. sanking

    sanking Member

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    If it is an XRite densitometer chances are good that the W setting Ron mentions will be designated as V, for Visual.

    How is the UV quantity filtered out? I have been curious to know if a color densitomer like the XRite 810 could read UV stain with an appropriate UV narrow band filter? Does anyone know if this is possible?

    Sandy
     
  6. Photo Engineer

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    Sandy;

    Most all densitometers in use have a filter for UV and IR both. There are some that measure UV density and some that measure IR density. Those are special purpose units designed for special purpose dyes.

    In addition, many B&W films contain UV absorbers in them especially in the support. All color films do. In color films, it is contained in a special layer of the film. The absorbance of the filter is similar to a Kodak 1B or 2B.

    Yes, the V setting or the W setting are identical, it depends on the make of the densitometer. It is here that the UV and IR filters are often used.

    Some brands rely on the fact that the film or paper absorbs UV, and have no UV filter in them. Mine has none, and uses a tungsten bulb which generates a little UV and quite a bit of IR. However, that is only metered in the V or W setting and silver has a rather flat curve in those regions IIRC. The color settings supply their own measure of UV and IR filtration being narrow band cutoff filters. They are smilar to the WR 98, 99 and 70 filters.

    PE