DIY light source for 10X10" enlarger.

Discussion in 'Darkroom Developing and Printing' started by jjs, Apr 9, 2008.

  1. jjs

    jjs Guest

    To date I've considered enlarger light sources to be engineering well beyond
    my feeble capability, but I have used and examined only condenser enlargers
    such as the Leitz IIa and Omega condenser enlarger, but my task now is to
    make a diffusion thpe for the 10x10 enlarger.

    I want something with No built-in filtration. No fancy color mixing for VC
    papers. No electronics. No side-lit mixing chambers. Just a straight forward
    light source and a diffusing layer. I question cold light, mercury vapor,
    tubes, whatever they are because I just don't plain understand 'em.

    I can blunder head-first into this project, but this group has some smart
    people with impressive experience, so I'll put my blunder idea forward.

    First, I am limited to ~110V AC power although converting to DC is an
    option. How about a simple array of 'white' LEDs at the top, pointing down
    over the typical sheet of plastic translucent material found in home supply
    places? Or should it be fine ground glass? I am not concerned about the
    variability of LEDs over time unless they change during the time it takes to
    get an 8X10 negative-to-print just right - maybe a day or two. The power for
    the light will be run through a robust power-conditioner once set aside for
    a big minicomputer. Batteries not included.

    So far so good? Corrections would be most welcome. OR just let me blunder
    and if it goes badly I'll post pictures of the catastrophe.
     
    jjs, Apr 9, 2008
    #1
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  2. A fluorescent light source of some kind -- a "cold light" source -- will
    give you the most light for the least power (and heat) unless you really
    want to use a *lot* of white LEDs. I'm not sure you can get enough output
    from a 10x10 grid of LEDs you assemble yourself to give decent enlarging
    times with a 10x10 negative, and I am also skeptical that it will be as
    even as you'd get with an array of fluorescent tubes.
     
    Thor Lancelot Simon, Apr 9, 2008
    #2
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  3. jjs

    jjs Guest

    This is great, Thor. I appreciate your input.

    Are these flourescent sources in round tubes? Or would it be a line of short
    tubes? And I gather that they would be left on all the time and I'd use the
    lens shutter, correct?
     
    jjs, Apr 9, 2008
    #3
  4. Incandescent bulbs are about 2% effiecient, LEDs 30-40% and flourescent
    bulbs about 60%. However more accurately a 15 watt flourescent bulb will
    replace a 100 watt bulb.

    There is a trade off. An incandescent bulb is a continuous spectrum light
    source, all the wavelengths of visible light (and some near IR and UV) are
    present. A flourescent bulb, even the ones sold as continuous spectrum plant
    lights puts out light in specific color bands. LEDs are even worse as far
    as spectrum output and white LEDs are very blue.

    This makes color printing near impossible without an incandescent bulb
    and will affect variable contrast paper and may affect regular paper.

    Incandescent lights have a very short on/off time. Flourescent ones
    take longer to start and fade more slowly. Therefore they are not
    good for short exposures. What a short exposure is, I can't say.

    LEDs are praticaly "instant on", but if you wanted 500 watts of incandescent
    light, you would need about 250 watts of LED. If you were to use Phillips
    high power LEDs, which run about 3 watts, you would need around 80 of them
    and some way to sink the 250 watts of heat. I don't know what they cost,
    but I expect that it would be an awfully expensive proposition.

    Small LEDs like the ones in flashlights are far smaller so you would need
    hundreds of them.

    I would build a box with regular lamp sockets and some sort of ventilation.
    Passive ventilation would be better for less vibration.

    I would place some sort of diffuser at the bottom, possibly several
    layers of "opal" glass.

    You could start with incandescent bulbs. If you run into heat problems,
    you could switch to CFLs (screw in compact flourescent lamps) but you
    may need some sort of shutter and delay unit. Properly sequenced, fan on
    normally, turn off fan, turn on lights, wait 5 seconds, and then open
    the shutter. When the exposure time expired, close shutter, turn off
    lamps and turn on fan.

    As for incandescent bulbs, you may have to find ones with the
    lettering on the side instead of the bottom.


    Geoff.
     
    Geoffrey S. Mendelson, Apr 9, 2008
    #4
  5. Fine ground glass, definitely. Which you can easily make yourself out of
    any ordinary window glass. (You know how to do that, right? using
    valve-grinding compound, etc.)

    I got my old Elwood 5x7 illuminating very sweetly by "tweaking" the
    glass diffusers that came with it (it had 3 sheets of glass in a
    sandwich). I ended up grinding one of them on both sides, which made a
    remarkable difference. "Tuned" it by making blank exposures (no neg) and
    checking for consistent gray tone across the field. (Most of the
    "tuning" consisted of rotating the light bulb with respect to the
    enlarger, so if you use a LED array, you probably won't have to do this.)
     
    David Nebenzahl, Apr 9, 2008
    #5
  6. There are ways to remove the lettering on the bottom. (Don't ask me how
    I know that.)
     
    David Nebenzahl, Apr 9, 2008
    #6
  7. jjs

    Ken Hart Guest

    Years agom I had a Solar brand 5x7 enlarger. The lamp head was a huge globe,
    possibly 16" in diameter, with a large base incandescent bulb. The globe was
    silver inside. There was a pair of diffusion glasses, separated by about one
    inch. The top glass had an additional diffusion spot in the center to offset
    the hotspot caused by the bulb.

    Why not a mixing chamber type system? Seems to me a reflective dome with two
    or three lights pointing in would be fairly simple. Plus, heat could be
    easier to handle because the bulbs would be 'sort of' outside the dome.

    My second choice would be flourescent. I don't know what's available, but
    surely someone makes a compact fixture about 12" long. Put several of them
    side by side in a reflective chamber and diffuse the output. You would have
    to use a shutter, and the color temp _might_ cause a problem with
    multi-contrast papers.

    And finally, here's an outside the box possiblity: Construct the enlarger so
    that the head is stationary and the baseboard moves. Open the head to the
    outside world, and use the biggest diffuser available, the sky!
     
    Ken Hart, Apr 9, 2008
    #7
  8. jjs

    jjs Guest

    This has been a terrific thread of brainstorming. I've learned a lot and
    also got pointers to things to explore further.

    In return for the good input (and in the original spirit of Usenet) I will
    look into the LED array simply to get a realistic idea of what it would cost
    for enough light, what the proper power supply would cost, and try to get
    the actual color temp of so-called white LEDs and post back. It will take a
    while.

    Ventilation for the heat is a good point. I've seen flexible tubes that go
    to a high volume, low speed blower mounted far from the object. The idea of
    using the sky is really "out of the box" :) and actually goes back to the
    old pre-electric, wet plate era where they did contacts only. (When I get
    all pissy about Film-is-Dead posts, I dream of exactly such a setup. No
    juice photography.)

    Oh - still on Ventilation -- very cool idea about putting lamps inside
    separate housings outside the head and pointing them into the mixing area.
    Given that this beast is about 1500 pounds and 12' tall already, it sure
    doesn't add any significant bulk.(Thinking I could have converted an
    Airstream trailer to a camera with as much bulk.)

    Finally, I must test the electric shutter on B for a few minutes. It was not
    used that way in its original camera, but I have a fused box on the bench
    and welding gloves. :)

    Tonight I will try to find time to do tentative drawings of a couple
    housings - one for traditional incandescents, and one for the external
    lights idea.

    Thank you all very much again,

    John
     
    jjs, Apr 9, 2008
    #8
  9. Cold light lamps are just fluorescent lamps. I think you
    could make a decent source by using an array of tubular
    fluorescents in a metal box with diffusion from plastic
    sheets. The plastic should work because the heat from the
    lamps is relatively low. Diffusing plastic that is nearly as
    good as opal glass is easily available and is both cheaper
    and a better diffuser than ground glass.
    Fluorescent lamps, like all gasseous discharge lamps,
    like to work hot and should be run continuously. Exposures
    should be made by usign a shutter over the lens. This was
    the standard setup for the old Saltzman enlagers which had
    something akin to a Packard shutter mounted on a rod below
    the lens in much the same way as the red filters on some
    enlargers.
    There are fluorescent lamps that can be used with
    variable contrast filters without too much limiting of the
    contrast range.
    My own project, which got put on hold for a while, was to
    make a suitable lamphouse for use with a view camera (Agfa)
    to rig it for enlarging while leaving it intact for use as a
    camera.
    Originally I intended to use a large electronic chassis
    for the light box but new ones are quite expensive. I
    suspect a sheet metal shop could make up a suitable box for
    less, at least worth a check.
    Arist makes a lamp that fits both the Saltzman and
    Elwood enlargers but its quite expensive and I am sure a
    satisfactory home made lamphouse could be made much more
    economically.
     
    Richard Knoppow, Apr 9, 2008
    #9
  10. jjs

    ____ Guest

    The Omega 10x10 that I have a diffused halogen light source is merely a
    white interior painted metal box with a fan on one side. Two halogen
    tubes about 5-6" long, commonly found at home depot or lowes are on the
    top surface, mounted about 3/4 foot apart. The Diffusion panel sits
    about 4-6 inches below and is straight through projection of the
    internal light. I have printed B&W with no unevenness. The diffusion
    panel IS the standard 10x10 panel used in Omega 10x10 enlargers -its
    milled with a cone peak in the center which distributes the light evenly.

    Omega sells the diffuser for 300.00 My lamp house has a single tray
    which I installed optical grade glass into to support the 10 x 10 VC
    filters bought from Calumet and made by ILford.


    Its a Very Simple design.
     
    ____, Apr 10, 2008
    #10
  11. jjs

    gr Guest

    Forget florescent lamps unless you run then continuous and use a
    shutter; even then they can vary intensity quite a bit. Tubes have a
    warm up vs output curve of 30 minutes or so, CF type take at least 5 min
    to come up close to full output. An integrator would allow use.

    If I was making a quick light box for an 8x10 enlarger, I would use
    multiple bulbs (4 or 6) (prob small qz halogen to distribute the light
    more evenly and then 2 white plex diffusers spaced 1-2" apart between
    the bulb and the neg.
    gr
     
    gr, Apr 10, 2008
    #11
  12. http://www.elektor.com/magazines/2008/february/power-to-the-leds.350167.lynkx

    You have to pay for the article, but the free description has some links to
    manufacturer's web sites.
    It does not have to be a very sophisticated shutter, a solenoid with
    a spring return, or a 1/2 turn stepper motor would do. We are not
    looking for exposure accuracy here, the electronics will handle
    that (even if it is a pushbutton switch and you control it).

    Remember that a 1% variation in exposure is not going to be noticable,
    and that could easily be 1/2 second. It depends upon how much straight
    printing you want to do versus dodging and burning. :)

    Good luck.

    Geoff.
     
    Geoffrey S. Mendelson, Apr 10, 2008
    #12
  13. "White" LEDs don't have a color temperature; they are not blackbody light
    sources. You're going to have the same problems you would with a fluorescent
    lamp, color-wise...
     
    Thor Lancelot Simon, Apr 10, 2008
    #13
  14. Yes and no -- they've got a somewhat unusual spectrum and they have
    special ballasts and a large preheater. The latter two differences
    from your run of the mill fluorescent lamp are meant to make them
    more useful for enlarging by reducing the warm up time that causes
    problems for short exposures.

    These are worthwhile differences but with an enlarging timer that
    measures light output, like the Metrolux, much less so.
     
    Thor Lancelot Simon, Apr 10, 2008
    #14
  15. jjs

    Peter Chant Guest

    I did see an article somewhere for an enlarger head using LED's but a mix of
    I think blue and green were used*, their output or exposure times were
    variable to give a multigrade head.

    *Seems an odd choice to me but the chap knows more than I do.

    Pete
     
    Peter Chant, Apr 10, 2008
    #15
  16. Use acetone. Fingernail polish remover will do--It's mostly acetone--but
    you'll need to use isopropyl alcohol (NOT rubbing alcohol--it contains
    oil) after to remove the additives in the polish remover left on the bulb
    that keep the nails from becoming dry and brittle.

    Stef
     
    Stefan Patric, Apr 10, 2008
    #16
  17. Not all cold light heads have the heaters. They are
    mostly on Arista lamphouses and are meant to maintain the
    light output of the lamp when not run continuously. The
    phosphors may be different but there are at least two types
    of lamp offered by Arista, one being balanced better for VC
    paper. One can buy several types of flourescent lamps
    including at least one phosphor with a visual color similar
    to incandescent lamps. The spectral outputs for the
    phosphors are available from most lamp manufactuers so its
    possible to see if the spectra is suitable for VC paper.
    I have no idea of what differences there are in the
    balasts other than to withstand intermittent operation.
    All gaseous discharge lamps have outputs which increase
    with temperature so they like to run hot. In a diy lamphouse
    the only method of getting consitent light output is to run
    the thing continuously and use a shutter to control the
    exposure.
     
    Richard Knoppow, Apr 10, 2008
    #17
  18. The problem with incandescent lamps is heat. Dissipating
    the heat will make construction of the housing more complex.
    If one uses an enlarging meter the variations of flourescent
    lamps with temperature is of much less importance. Even
    though flourescent lamps like to run hot the heat involved
    is still much less than it would be for incandescent lamps
    of similar output.
     
    Richard Knoppow, Apr 10, 2008
    #18
  19. I've never heard of cyan LEDs. Green and blue will look cyan to the
    eye, but I have no idea if it will activate that layer, my guess is
    not.

    Geoff.
     
    Geoffrey S. Mendelson, Apr 10, 2008
    #19
  20. JJS,

    IIRC, one of the Ansel Adams Photo Series books from years ago had
    detailed instructions on how Adams built a diffusion head light source
    for a horizontal enlarger made from a salvaged 8x10 camera. It used an
    array of small incandescent bulbs, opal glass for diffusion, and a vacuum
    cleaner for heat removal. Very simple.

    I adapted the design to a vertical 4x5 enlarger, using below-the-lens VC
    filters. Worked quite well, but when I could afford it, I replaced it
    with an Aristo head color balanced for VC paper.

    Stef
     
    Stefan Patric, Apr 10, 2008
    #20
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