DIY cold(ish) light head.

Discussion in 'Darkroom Developing and Printing' started by Peter Chant, Sep 30, 2004.

  1. Peter Chant

    Peter Chant Guest

    I am just wondering if it is possible to make a DIY cold light head
    by mounting compact flourescent lamps in a white box held above the neg
    carrier. They might need a diffuser, but if the box were white and the
    tubes far enough above the film plane I suspect it might work.

    The only issues I can think of is that some of these lamps start with
    a bit of a flicker, that some take a while to get to maximum brightness
    and that the spectum might cause issues with multigrade paper.

    Any thoughts? Has anyone tried this?
     
    Peter Chant, Sep 30, 2004
    #1
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  2. Peter Chant

    jjs Guest

    Leave the light on full-time and put a shutter on the lens. There are
    solenoids that you can use to time the shutter (B) setting.
     
    jjs, Sep 30, 2004
    #2
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  3. Peter Chant

    Alan Smithee Guest

    You might try this link. I'm not sure what is better for B&W, condensor,
    diffuse or cold. Perhaps someone can explain the advantages of each. I'm
    currently using my condensor but I'm thinking of switching to the dichro and
    utilizing the "filter" method for contrast control on VC paper.

    http://www.largeformatphotography.info/lfforum/topic/211868.html
     
    Alan Smithee, Sep 30, 2004
    #3
  4. Yes, but it is not so easy.
    If the 'box' is properly built you will not need a diffuser.
    Barium or Titanium dioxide. Kodak makes(made?) a white spray paint
    for this purpose.
    Nope, the light source is to the side and mounted in a pipe/recess. The
    light shines on the far wall of the integrating sphere/box, bounces around
    and illuminates all the inside surfaces of the box equally (this is theory:
    the sphere must be 100% reflective and there can be no holes in the sphere -
    like for the light to get in or the light to get out.) In any case, it
    works 'Good Enough' (especially with GE light bulbs - and you thought the
    letters stood for 'General Electric'.). The light comming from the box is
    'spooky' - all you see is light: no shadow or detail - and so it looks sort of
    like a hole into the infinite.

    If you make one make sure the negative never 'sees' the light source(s).

    The output of the sphere is a perfect diffuse source.

    Color heads make use the integration with three beams of light (CYM) entering
    the
    sphere. The light that comes out is a perfect (cough) mixture of the
    three entering colors.
    That's a _big_ issue. Fluorescent bulbs make dandy thermometers and it takes
    minutes for them to stabilize. It is possible to expose with a florescent (arc)
    lightsource, but you need an integrating exposure meter (called just an
    'integrator' in the graphic arts industry). The light probe must be
    filtered so that the probe's spectral sensitivity matches the papers -
    the light spectrum also changes as the lamp warms up.

    Aristo cold light heads use a heater to keep the lamp warm even when it is off.

    The best solution is leaving the light on all the time (then the lamp
    tracks room temperature, and that's GE).

    In the case of an integrating sphere you would place the shutter at the tube
    where the light enters the sphere.

    A better solution is to use a halogen bulb (as used in slide projectors) instead
    of a fluorescent. The big draw of a cold-light head is that it is a diffuse
    light
    source - there is nothing special about it being 'fluorescent.
    Yup. You need to have the same polycontrast filters in front of the integrator
    probe that you are using to expose the paper. It is easier to have two
    light sources (plus maybe a third white source for focusing) for the green and
    blue parts of the spectrum.
    Lots of experience when either 5KW arc lamps or small LEDs are used for
    illumination - graphic arts and clinical chemistry.

    I have a Beseler 45MX condenser enalrger in the darkroom - I sold the
    cold-light D3 Omega. I also have integrators coming out of my ears
    down in the basement. That may say something.
     
    Nicholas O. Lindan, Sep 30, 2004
    #4
  5. Peter Chant

    Nick Zentena Guest


    How did the Omega head that used a cicular tube work? Was that round tube
    off to the side?

    I've got an old book with design ideas for enlargers. In the section on
    disffusion enlargers IIRC it talks about using two diffusers about 1" apart.

    I want to build a 5x7 head myself using a large light fixture. So I'm
    curious about all this.

    Nick
     
    Nick Zentena, Sep 30, 2004
    #5
  6. Lynn Radeka uses such a system. He uses some of the instant on compact
    flourescent bulbs. Check out his website to see if he mentions it. If
    not, try asking by email.

    -Peter De Smidt
     
    Peter De Smidt, Sep 30, 2004
    #6
  7. Peter Chant

    John Walton Guest

    The prices of the emitters are coming down -- you have to be careful about
    the heat-sinking. One of the co-venture partners sent me some samples but
    I've been too busy with other stuff.
     
    John Walton, Sep 30, 2004
    #7
  8. Peter Chant

    Mike King Guest

    The Omega used a circular tube that sort of surrounded the film stage, the
    head was an oblate sphere-oid (shaped like a Kaiser roll) and the light on
    the film was all reflected. The example I played with was not in very good
    shape, most of the reflective coating on the head's interior had flaked off.
    It didn't flicker-much-and exposure times were quite long so the "surge" was
    insignificant in the total exposure.
     
    Mike King, Sep 30, 2004
    #8
  9. AFAIK the round tube was in a round gutter and shone up to illuminate the
    underside of the cap. The bright inside surface of the cap was then the
    light source the negative saw. The tube never illuminated the
    negative directly. I don't remember seeing a diffuser glass, but there may
    have been one.
    I had an old (1930's vintage) Federal enlarger that was built that way.
    The top diffuser was ground glass and the bottom one was opal.
    Very inefficient design. Opal glass only transmits 20-30% and frosted about
    50%, so the combination was 10-15%.

    A holographic diffuser would be a great a solution: high efficiency and
    even diffusion. The catch: a 5x7" sheet may run $300 or so.
    I would look at an old Elwood. Parabolic reflector and a diffuser glass
    above the negative. I ember someone saying they hot-spotted ...
     
    Nicholas O. Lindan, Sep 30, 2004
    #9
  10. Why? Condenser is better.
     
    Uranium Committee, Oct 1, 2004
    #10
  11. Peter Chant

    Dan Quinn Guest

    RE: (Peter Chant) wrote
    Back around 58-59 I picked up a war surplus unit, 4x5. It had
    4 or 5 small diameter short flourescent bulbs. AFAIK it
    worked OK. Dan
     
    Dan Quinn, Oct 1, 2004
    #11
  12. Do you mean the Luxeon leds ?
    I've a similar project (Color/VC head) for my Focomat IIc in the pipeline
    for next year.
    Maybe we can share some experiences ...

    Regards,
     
    Claudio Bonavolta, Oct 2, 2004
    #12
  13. Peter Chant

    John Walton Guest

    I have an RGB Controller PCB built -- it uses a BX24 micro-controller for
    each of the Emitters and a set of constant current sources -- just haven't
    had the time to wire it up. The original board had a "boost" switching
    power supply on board for strings of LED's.

    Jack
     
    John Walton, Oct 2, 2004
    #13
  14. Well, I'm still in the brain-storming phase ...
    I'll pilot it through my lab hardware/software:
    http://www.bonavolta.ch/hobby/en/photo/labsoftV3.htm
    to continue with an integrated solution (I should put an update pretty
    soon).
    I'll probably use three digital outputs, one per color channel, and variable
    exposures while keeping the full output power instead of trying to dim the
    leds.

    Regarding the type of led, I'm still unsure and have to buy some samples to
    check the output power.
    I like the Star because they already integrate part of the cooling, adding
    the rest looks easier.
    The emitters need a very special printed board to let the heat go through it
    to the cooler, Luxeon have a specific documentation regarding the cooling,
    looks like an important point.

    Nice to see someone else has a similar project, I'll be happy to hear from
    time to time how your project goes on.
    My email is on my website.

    Regards,
     
    Claudio Bonavolta, Oct 2, 2004
    #14
  15. Peter Chant

    Peter Chant Guest

    A slow response from the OP, me:

    No mention on his site.
     
    Peter Chant, Oct 4, 2004
    #15
  16. Peter Chant

    Peter Chant Guest

    Why? Condenser is better.[/QUOTE]

    It was to do with not having the right combination of condensers
    available. Hopefully fixed when tomorrows post arrives.
     
    Peter Chant, Oct 4, 2004
    #16
  17. Peter Chant

    Peter Chant Guest

    I presume you clamp something on the bottom of the lens?
     
    Peter Chant, Oct 4, 2004
    #17
  18. Peter Chant

    Peter Chant Guest

    Hmm, I was not planning on being this sophisticated. I thought that
    modern 'brilliant white' paints contained some form of titanium oxide?
    Anyway, what is wrong with any old white paint?
    A cardboard mock up worked reasonably well for a proof of concept. However
    it did show a little care would be needed with the white box.
    That I found by trial and error. No matter how far away I held the bulb
    it still formed an image of sorts on the base board.
    A bit tricky to make. I suspect an evenly illuminated section of
    an infinitely large sphere (flat plate) might work.
    Hmm, a PITA.
    Would that illuminate it evenly? Maybe a hemisphere illuminated around the
    edge would be a good plan?


    Cheers, an interesting post.
     
    Peter Chant, Oct 4, 2004
    #18
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