Need exposure unit measurement

Discussion in 'Contact Printing' started by mark, Oct 1, 2006.

  1. mark

    mark Member

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    I am making a UV box and am going to use spiral bulbs.

    Can some one tell me how tall your box is.
     
  2. Monophoto

    Monophoto Member

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    Mark -

    My box is also designed around spiral bulbs. There are six bulbs, two rows of three, on 6" centers. I read somewhere (don't remember where) that this was the optimum spacing.

    I also read somewhere that the spacing from the tip of the bulb to the top of the glass in the contact frame should be about the same as the center-to-center spacing between bulbs. That is supposed to be the optimum compromise between too close (shorter exposure time, but with a risk of hot-spots) and too far (even illumination, but longer exposure times).

    Obviously, the total height of the box has to be the sum of:
    the thickness of the contact frame
    the design spacing
    the height of the bulb from tip to the top of the base
    the height of the base
    In my case, that adds up to about 12", but may be different for you.

    Don't know if the dimesions make sense scientifically, but the box appears to give even illumination, and the exposure time for Pt/Pd is a reasonable 10-15 minutes.
     
  3. mark

    mark Member

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    Thanks. That is about what I figured. But I guess I should wait for my bulbs. Jumping the gun I guess.
     
  4. Salmonoid

    Salmonoid Member

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    Are these spiral bulbs that you are using the ones designed to replace regular incandecent light bulbs used in household lamps?
     
  5. cperez

    cperez Member

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    Patrick Kolb, Ray Bidegain and I built and are building UV light boxes using the spiral BLB bulbs.

    In our case, thus far we try to get the bulb to contact printer distance to be around 3 to 5 inches. This means with the depth of the contact printer frame, the length of the 27watt bulbs, length of the bulbs mounted in ceramic holders, and the space needed behind the ceramic holders to wire up the system, we're around 17 inches in total height (from the base of the UV box to the top). We have 6 bulbs centered and a fan to extract the heat.

    Using this setup, Patrick has been getting some really nice prints. I don't recall his exposure time, but mine on Crane's has been around 20 to 24 minutes with either Polaroid Type55 or Ilford FP4+ in Rodinal. My time will likely change as I move to a contact printer with glass that doesn't absorb as much UV light as my present contact printer does. Oh, and I'm not using B&S' system, I'm using Photographers Formulary (the "old" system, as I understand it).

    I hope this helps. I tend to ramble. :smile:
     
  6. menglert

    menglert Member

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    Here is a LINK to some info on how I built my UV box.

    I would make a few changes in retrospect. As the previous post suggested, I would build it a bit higher, as itÂ’s easier to adjust the height of the contact printing frame later. I moved from a contact frame (glass sandwich) to a vacuum frame, and when I retest with the vacuum frame I will likely have to some how raise the whole exposure unit to accommodate for the increased height of the vacuum frame. In addition, if you plan to do larger formats in the future I would build a larger box and prewire (is that a word?) all the sockets.

    I did build a larger box, but failed to prewire everything at that time, and now when I decide to move up to larger prints I will have to add more sockets.

    Hope this helps some.

    Regards,
    Martin
     
  7. cperez

    cperez Member

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    OK, I lie like a cheap rug. The total height is 14 inches. Not an inch more or less. I corrected my statement below.

     
  8. mark

    mark Member

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    Okay, the spiral bulb idea went on hold, when I realized I did not have a lot of time to devote to the building. Martin's website is great and his link to the Sgutterbug site was fantastic. Thanks Martin. That unit looks to be a much more doable project for me with my limited time.
     
  9. cperez

    cperez Member

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    Mark, it took us 3 hours to cut the wood, wire the holders, construct the sides (including a neat little door that keeps the contact print from from hitting the bulbs), install the muffin fan, and complete the wiring. I probably spent an hour at the local lumber/electrical supply.

    I hope this helps.

     
  10. mark

    mark Member

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    Really. Hmmm.