Homemade UV Light Box help

Discussion in 'Alternative Processes' started by htswv, Dec 3, 2005.

  1. htswv

    htswv Member

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    Hello everyone!

    I am in the process of building a light box according to the specifications on the Edwards Engineering website. I have the box frame completed and just installed the bi-pin lampholders today. The problem is that the lamps are not exactly evenly spaced. There are no large gaps between them but instead the spaces between the lamps vary +/- 1/4 of an inch...some are a little closer together than others. I was just wondering what (if any) impact this may have on the resulting prints? I tried my best to get them PERFECTLY aligned but I just couldn't seem to manage it. Should I start again? If this is a problem, would installing a piece of galvanized sheet metal behind the lamps and painting the inside of the box white help to even out the light?

    Thanks to anyone that can help!

    Christian
     
  2. Donald Miller

    Donald Miller Member

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    My initial thought is that it may not make a big difference...however, the best way to find out is to try it. It would appear the you have nothing to lose by trying.

    Most paints and other reflective surfaces are not terribly efficient at reflecting UV.
     
  3. sanking

    sanking Member

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    If you use the unit with the tubes spaced about four inches over the printing frame the small variations you describe will have no measurable impact on eveness of illumination on your prints.

    Sandy




     
  4. matt miller

    matt miller Subscriber

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    I, too, built a uv unit from the Edwards plans. I modified the plans a little though. I have 8 bulbs, instead of 12. I have a 1/2 inch of space between my bulbs. At the beginning I had trouble with getting the lights all started. I ended up putting a galvanized sheet behind the lamps and it did the trick. It had something to do with grounding. I painted the entire exposure chamber white, including the galvanized sheet. With the Edwards plans, the unit doesn't allow four inches of space from the lamps to the printing frame. It's more like 2 inches with the frame (B&S) that I use. I don't get any striping or areas of uneven exposure with my unit.
     
  5. juan

    juan Subscriber

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    I made a UV printer using a box I already had and put four 15-watt spiral BLB bulbs in it. I used the standard porcelain lampholders from the hardware store to mount them. The lampholders put the bulbs 2 1/2 inches apart, and they are about 2 inches above the paper. I painted the inside of the box white. My largest negative is 8x10.

    Exposures for VDB made with negatives made for Grade 2 Azo run 11-12 minutes. I don't see any sign of a gap in the exposure. I do see a problem with falloff on the ends of a 10" print if I am not very careful in placing the paper exactly in the center. I may get two more bulbes to make the unit longer.

    Advantages of these bulbs are that ballast is built in. They are just like the squiggly flourescent bulbs made to replace regular light bulbs in your home, except these bulbs are BLB. The cost $9.55 each at my local light bulb warehouse.
    juan
     
  6. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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    I got my lamps in an already-made blacklight fixture from Home Depot - they're about $15 each for the whole thing, including the BLB bulb. I got six of them, and the bulbs are about an inch and a half apart. I just mounted them on the underside of an Ikea shelving unit that my 4x5 enlarger sits on, and put a second shelf about six inches below them, so that the film/paper sandwich is about 3" away. This gives me 7 1/2 minute exposures with good negatives, or 15 minutes with a denser neg. I've done nothing else to enclose or otherwise reflect additional UV back at the printing frame. Once I have some more woodworking skills, I'll build a discrete box for them, but for now, the shelf thing works just fine.
     
  7. OldBikerPete

    OldBikerPete Member

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    I have a UV light box I made for a copper etching process.
    I lined the inside of it with aluminium foil instead of painting the box.
     
  8. htswv

    htswv Member

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    Okay...the light box is finally "finished!" Except there seems to be one minor problem. When I power up the unit all of the tubes come on at the same time. However four of the bulbs seem dimmer than the others. Of these four, two bulbs take a few seconds to reach the same level of brightness as the others but THE OTHER TWO seem to stay "dim." I know these two are working because if I take them out they are much darker than the others. Both of these bulbs are controlled by the same ballast. I've tried different bulbs, checked all of the wiring, etc but nothing seems to help. Would you suspect the ballast?

    PS. I'm building this box according to the Edwards plans and I have also installed a grounded metal reflector behind the lamps to prevent what others on here have found to be a common grounding problem.

    Please help if you can!

    Christian
     
  9. juan

    juan Subscriber

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    Some of mine appear dimmer than others, but remember the light you are concerned about is not the visible light. I'd say try it with a sheet of paper and see if you can see any variation in the light in the print. I can't see any difference in mine.
    juan