Acrylic sheet to replace glass in carrier?

Discussion in 'Enlarging' started by batwister, Apr 17, 2012.

  1. batwister

    batwister Member

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    I've had problems with a rebate reflection in my negative carrier, which I've discovered is caused by the bottom sheet of glass.
    Would a piece of acryllic of the same thickness and size, with a 6cm square hole for the negative, be an adequate replacement?

    In particular I'm wondering about damage the acrylic might cause to the negatives (acid?), as well as potential flexing when the acrylic is warmed by the lamp and then cooled.
     
  2. richard ide

    richard ide Subscriber

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    Acrylic would soon show scratches so really leaves a lot to be desired for an optical application like this. Would not making a mask for your glass carrier be a better solution?
     
  3. Ian Grant

    Ian Grant Subscriber

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    I used a lot of acrylics commercially amd agree with Richard they scratch. What enlarger, I've never had issues with glass.

    Ian
     
  4. Leigh Youdale

    Leigh Youdale Member

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    Without knowing more about the model of enlarger and details of the negative carrier, I'm wondering (speculating) if the problem is not the glass itself but that the glass is diffracting a reflection source from the tracks in the carrier? I'd want to check for any bright spots that may be the results of wear between the carrier and the tracks it slides in.
     
  5. Leigh B

    Leigh B Member

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    The maximum operating temperature for acrylic is either 150°F or 170°F, depending on the type.

    The operating temperature of a halogen bulb is 700°F.
    Non-halogen enlarger bulbs run at lower temperatures, but I wouldn't trust acrylic even with those.

    - Leigh
     
  6. darkroom_rookie

    darkroom_rookie Member

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    Use Lexan polycarbonate sheets. I replaced a bottom diffuser in a mixing box of an enlarger that has a 200W 24V bulb with a 2mm Lexan sheet and it passed the several-hour test. It is milky white, though, and very hard and glossy on one side while the other is slightly matt. There are clear versions available and likely free - ask for samples (mine's a sample). They deliver them protected on both sides.
     
  7. batwister

    batwister Member

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  8. DREW WILEY

    DREW WILEY Member

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    Neither acrylic nor polycarbonate will remain flat without bowing, so would be worthless in a neg
    carrier. Stray light can be masked off. Or if it's bouncing off the actual edges of the glass, simply
    paint these with a stroke of a black Magic Marker or Sharpie pen.
     
  9. Bob-D659

    Bob-D659 Member

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    That looks very similar to a Durst carrier, Durst blackened the beveled edges at the factory on the glass inserts I have. Those glass inserts look a little too thick as well, they should just be a tiny bit proud of the metal frame. You could make an aluminum insert for a glassless carrier, I did that with 1.5mm thick aluminum sheet for both the lower and upper glasses on the D659 enlarger. File out the hole to match your negative image area. The D606 and others use the same 1.5mm glass inserts.
     
  10. batwister

    batwister Member

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    They are pretty thick. There's an extra, thinner piece of glass that came with the enlarger, which I really can't get my head around. Obviously this doesn't sit flat with the thicker top piece and neither does it solve the reflection problem. My enlarger is a Krokus 3 by the way.

    I'd be very worried about scratches to the negative with aluminium, even if I was extra careful filing. Isn't this a problem with yours?
     
  11. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    Plastics sometimes have a static charge which can attract dust which is problematic.
     
  12. Bob-D659

    Bob-D659 Member

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    Well I used a milling machine to make the masks, then file a bevel in the port for the negative and finish with 200, 400, 800 and finally 1,000 grit wet and dry paper. The file cut edges are as smooth as glass.

    You can even use mat board to make a mask. it is just a bit fragile.
     
  13. ic-racer

    ic-racer Member

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    Can you post an example?
     
  14. Bob-D659

    Bob-D659 Member

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  15. ic-racer

    ic-racer Member

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    Does anyone know what that is an image of? What is the gray at the R side? Why is there something that looks like another negative forming a white rectangle at the top? Where are the edges of the negative carrier in that print? Where is the negative rebate? I can't see any edge markings. Are they masked out? Is there any masking? Why not?
     
  16. batwister

    batwister Member

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    I can understand why it looks confusing. The image with the tree on the bottom left is the top of the print where the reflection was evident, the image on the right is the left side of the print where the reflection was evident, the top white with the fuzzy line is blank paper. It's a composite of parts of the print in essence. The rebate is all the black.
     
  17. ic-racer

    ic-racer Member

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    I see it now. Very odd.
     
  18. Bob-D659

    Bob-D659 Member

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    Do you use the carrier with the adjustable masks wide open or do you close them down a little. Closing them a little should get rid of the edge distortion unless the glass is too thick.

    How thick is the gap between the upper and lower metal halves when it is closed? Without a negative between the glass plates, it should almost clamp a piece of film between the upper and lower metal frames.

    Are both pieces of glass the same thickness?
     
  19. Michael R 1974

    Michael R 1974 Subscriber

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    I still think it's reflection off the easel frame. Try making the print with no easel to test.
     
  20. batwister

    batwister Member

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    The masks on the carrier are wide open - that's to say, I don't use them. With the masks up to the edge of the rebate the problem is still apparent.

    Not entirely sure I understand you.

    Yes.
     
  21. batwister

    batwister Member

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    Done this yeah.
     
  22. Michael R 1974

    Michael R 1974 Subscriber

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    I'm really stumped then. I've never seen this happen other than when light reflects of a thick easel frame. This is all very strange. Then again I have no experience with your particular enlarger. Curious.
     
  23. Bob-D659

    Bob-D659 Member

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    If the glass is too thick, you will get internal reflections off the beveled edges, the moveable masks are there to eliminate excess light spill onto the easel. Try moving them in a 1/4" or so and see if the problem still exists.

    If the glass is too thick, they may not sit flat against the whole surface of the negative when the carrier is in the enlarger, causing all sorts of weird abnormalities.

    I'm just throwing out ideas for you to check, not having ever see that model of enlarger, but have seen may weird things from poorly modified ones.