Acrylic sheet to replace glass in carrier?

batwister · Apr 17, 2012

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.

richard ide · Apr 17, 2012

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?

Ian Grant · Apr 17, 2012

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

Ian

Leigh Youdale · Apr 17, 2012

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.

Leigh B · Apr 17, 2012

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

darkroom_rookie · Apr 18, 2012

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.

batwister · Apr 18, 2012

Here's the carrier http://1.bp.blogspot.com/-acDU5Xi2t_A/T48QABRfi1I/AAAAAAAAAJM/a9nBW07ITXc/s1600/negativecarrier.jpg

I've decided to make a mask, which will need to replace the bottom sheet of glass and hold the negative. It has to be 3mm thick. Not sure what the best material would be.

DREW WILEY · Apr 18, 2012

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.

Bob-D659 · Apr 18, 2012

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.

batwister · Apr 18, 2012

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?

Mainecoonmaniac · Apr 18, 2012

Plastics sometimes have a static charge which can attract dust which is problematic.

Bob-D659 · Apr 19, 2012

batwister said:
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?

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.

ic-racer · Apr 19, 2012

batwister said:
I've had problems with a rebate reflection in my negative carrier, which I've discovered is caused by the bottom sheet of glass.

Can you post an example?

Bob-D659 · Apr 20, 2012

I think this is the thread with an example.

(there was a url link here which no longer exists)

ic-racer · Apr 22, 2012

Bob-D659 said:
I think this is the thread with an example.

(there was a url link here which no longer exists)

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?

batwister · Apr 22, 2012

ic-racer said:
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?

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.

ic-racer · Apr 23, 2012

batwister said:
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.

I see it now. Very odd.

Bob-D659 · Apr 23, 2012

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?

batwister · Apr 23, 2012

Bob-D659 said:
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.

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.

Bob-D659 said:
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.

Not entirely sure I understand you.

Bob-D659 said:
Are both pieces of glass the same thickness?

Yes.

batwister · Apr 23, 2012

Michael R 1974 said:
I still think it's reflection off the easel frame. Try making the print with no easel to test.

Done this yeah.

Bob-D659 · Apr 23, 2012

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.

Acrylic sheet to replace glass in carrier?

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