Is polycarbonate a good alternative to anti-newton glass?

[1kgcoffee]

I was reading this old thread over at photo.net where someone discusses using polycarbonate to project medium format slides. Got me thinking of all the possible applications, not least of which is as a negative carrier that can be wet mounted upon or wet plates suitable for enlargement.

I sandwich the Velvia slides between polycarbonate strips (1/16th") and slide the strips horizontally through the gate between lens and condenser. I've built a track to hold the strips parallel to the lens barrel and can show four or five 6x6 or 6x7 or 6x8 slides in sequence with no darkening of the screen.

So has anyone tried this? Thoughts? The idea has me excited as polycarbonate is durable and thin and supposedly transparent.

 

[wiltw]

Newton rings caused by the 'interference' pattern...I rather doubt shiny polycarbonate is any different than shiny glass!

 

[AgX]

Yes, I too do not get the OP's idea on that.
Polycabonate behaves optically like a flat glass plane. Aside of different breaking index and mayby parallelity of planes, depending on kind of manufacture.

To avoid newton rings one must care not to create uniform space between planes in the wavelenghth scale. This is done by (micro-) roughening the carrier panes or the film.

With what I wrote above, one could argue that a polycarbonate pane might be more wavy than the standard pane used in a film stage, thus concquering the forming Newton rings, but that wavyness again would have effect on image quality.

 

[L Gebhardt]

Polycarbonate scratches easier than glass, so it won’t be as durable. And as others have said newton rings are a reflection and interference issue. So I don’t expect it to be a great solution. But it’s cheap enough to test, and it may turn out it’s just uneven enough to breakup the rings.

 

[koraks]

I can imagine polycarbonate being easier to manipulate in such a way that the surface resembles that of proper AN glass. I imagine that a chemical approach would be possible. With glass, it would take treatment with HF and that's obviously out of the question in a DIY setting for the vast majority of us (save for the actively suicidal, perhaps).

 

[ic-racer]

DId they stop making AN glass? I have 3 new-to me glass carriers that I was planning on adding new AN glass and did not anticipate and issues with the supply of glass.

 

[koraks]

At least in Europe it's pretty hard to find. And expensive too.

 

[AgX]

Available off the shelf in 6x6 (nominal). No idea on the price though

 

[GRHazelton]

Hanging around Wings Camera in Atlanta, my source for used gear, somehow the conversation turned to Newton's Rings. An old hand, who'd done newspaper shooting, said that they used to use a light dusting of talc on a glass neg carrier! I suppose the fine grains separated the neg from the glass just enough; with moderate enlargement the grains wouldn't be visible. Of course YMMV.

 

[jim10219]

Yeah it works. They make polycarbonate sheets (often under the brand name Lexan) with anti-glare coatings (basically once side is slightly roughed up). Same with Acrylic (Plexiglass). Though, if you're going to wet mount, that defeats the purpose of using AN glass or substitutes. The downside to these plastic sheets vs. glass is they scratch easier. A LOT easier. I've tried them and given up on using them for photography due to their ease of scratching. It seems cheaper at first, but in the long run it's going to be cheaper to use glass, as the plastic ones scratch so easily, they're almost one-time use.

I also don't use any AN glass anymore for anything. I struggled with it for a while trying to make it work, but in my experience, it always takes away some of the sharpness and there are better methods out there. For scanning, I wet mount. For enlarging, I use glassless negative carriers and either LED lamps or heat absorbing glass and quick exposure times. If it's a particularly curly negative, I'll tape it down with some of that 3M low tack adhesive tape. For alternative process contact printing, I ignore the Newton rings, as they don't actually show up in the prints. I wanted AN glass to work as it would have been easier to deal with. But I never could get past the lack of sharpness it gave me. It might be alright for some people. But it just didn't work for me.

 

[koraks]

Available off the shelf in 6x6 (nominal). No idea on the price though

I never looked for 6x6, but 5x7" is not very easy to get.

 

[Billy Axeman]

At least in Europe it's pretty hard to find. And expensive too.

Kaiser is using AN glass in negative carriers in their System V enlargers. Currently these AN glass inserts are offered by Fotoimpex in Berlin (Germany). They are 100 x 72.5 mm (3.9 x 2.9 in.).

 

[AgX]

I was referring to the Kaiser glass panes too, however I did not scroll far enough at their site (fool I am) to see that they actually sell that big ones too, as their framing stages only go to 6x7. But the big panes are to be used without any framing device. Large enough for DIY cut solutions. However one then must not forget to ground bevel or even polish the edges.

 

[DREW WILEY]

I've done extensive experiments on this issue, involving a considerable variety of glass as well as plastic. Polycarbonate has a crystalline cross-bonded molecular structure which resists slow moisture intake much better than acrylic, but it is yellower. Acrylic has about about 8% better light transmission with very little hue bias; but it is molecularly like a lot of spaghetti strands thrown atop one another without any tertiary bonding, so will slowly hydrate and warp unless you've purchased a special baked-out type. But you can get acrylic slightly textured on one side if you want to try that for suppressing rings. It's sold as non-glare acrylic for picture framers. Don't confuse this with inferior styrene sheets. But the main problem with all these plastics is that they tend to warp in the direction of heat and light and might not remain truly flat in a negative carrier like real glass does. They also scratch easily. I haven't tried optically coated acrylic yet; it's far more expensive than coated glass, which itself didn't do the trick of mitigating rings for me. I'm in a foggy damp coastal climate where rings are a persistent issue. If you're just dealing with negs as small as 6X7 try to locate some old Gepe anti-Newton slide mounts. Each one will very affordably give you two sheets of thin high quality AN glass.

 

[jim10219]

I've done extensive experiments on this issue, involving a considerable variety of glass as well as plastic. Polycarbonate has a crystalline cross-bonded molecular structure which resists slow moisture intake much better than acrylic, but it is yellower. Acrylic has about about 8% better light transmission with very little hue bias; but it is molecularly like a lot of spaghetti strands thrown atop one another without any tertiary bonding, so will slowly hydrate and warp unless you've purchased a special baked-out type. But you can get acrylic slightly textured on one side if you want to try that for suppressing rings. It's sold as non-glare acrylic for picture framers. Don't confuse this with inferior styrene sheets. But the main problem with all these plastics is that they tend to warp in the direction of heat and light and might not remain truly flat in a negative carrier like real glass does. They also scratch easily. I haven't tried optically coated acrylic yet; it's far more expensive than coated glass, which itself didn't do the trick of mitigating rings for me. I'm in a foggy damp coastal climate where rings are a persistent issue. If you're just dealing with negs as small as 6X7 try to locate some old Gepe anti-Newton slide mounts. Each one will very affordably give you two sheets of thin high quality AN glass.

Oh yeah. I forgot about the dimensional stability of plastic. In my experiments, I didn't see an issue with warping (but didn't look too closely) but did have an issue with them expanding under heat. I remember having to shave the polycarbonate sheets about 1/8" in my contact printing frame when doing alternative process photography, or else the sheets would expand and get stuck in the frame, and on my homemade frame, you access the paper by removing the glass. So having to wait 15 minutes in the dark after a 3 minute exposure just to get the print out for development was no fun.

 

[M Carter]

I also don't use any AN glass anymore for anything. I struggled with it for a while trying to make it work, but in my experience, it always takes away some of the sharpness and there are better methods out there. For scanning, I wet mount. For enlarging, I use glassless negative carriers and either LED lamps or heat absorbing glass and quick exposure times. If it's a particularly curly negative, I'll tape it down with some of that 3M low tack adhesive tape. For alternative process contact printing, I ignore the Newton rings, as they don't actually show up in the prints. I wanted AN glass to work as it would have been easier to deal with. But I never could get past the lack of sharpness it gave me. It might be alright for some people. But it just didn't work for me.

Glass carriers are a must for me, since I do the pin registered masking thing. But I've used 2 different plain-glass carriers (stock Beseler and a Radeka setup) and never seen a Newton ring, with Acros, HP5, Delta 100, etc. - all the normal films. Maybe I've been lucky? I'm doing 16x20 and 20x24 prints, condenser enlarger.

 

[koraks]

Maybe I've been lucky?

Yes. I've seen newton rings in just about any configuration imaginable. Contact printing frames, contact printing under loose sheets of glass, on scanner platens - heck, even on a glass nevative carrier...with AN glass. So YMMV and count your blessings

 

[bernard_L]

But you can get acrylic slightly textured on one side if you want to try that for suppressing rings. It's sold as non-glare acrylic for picture framers. Don't confuse this with inferior styrene sheets. But the main problem with all these plastics is that they tend to warp in the direction of heat and light and might not remain truly flat in a negative carrier like real glass does. They also scratch easily.

Why stop halfway towards a solution? Picture framers also sell slightly textured glass (at least where I live). They call it anti-glare, but of course it is nothing like vacuum coated "museum" glass; Fort me it works, at least in the position between light source and lens, in a one-glass carrier.

 

[Billy Axeman]

Why stop halfway towards a solution? Picture framers also sell slightly textured glass (at least where I live). They call it anti-glare, but of course it is nothing like vacuum coated "museum" glass; Fort me it works, at least in the position between light source and lens, in a one-glass carrier.

I have compared NR glass (from Kaiser) with textured glass as protection for framed artwork with a strong loupe and this latter glass had the same texture as the AN glass but its surface roughness was more coarse (with bigger bubbles).

I guess the AN glass is made by sanding the surface with a carborundum powder (silicon carbide) and then etching it to smooth it out. The coarseness of the surface is determined by the grit size of the carborundum powder. In the most ideal case the surface roughness must be (much) smaller than the grain on the film otherwise it could be visible in a copy (assuming your scanner has sufficient resolution to scan the grain).

So, at first sight ordinary glass for picture frames could be used as AN glass but a test is needed on a blank part of the film to see if the roughness of the glass is visible or not.

 

[DREW WILEY]

There are various ways AN was made, either by coating on a textured surface or by altering the surface of the glass itself. There were once many variations, and I myself at one time had about 13 different varieties on hand for testing. The best glass was made in Belgium in various thicknesses; but a thin variety was purchased by both Durst and Omega and has more of a subtle ripple pattern to it rather than a dimpled or frosted one. AN is not made by grinding per se like a ground glass intended for view camera focus. Ordinary non-glare picture glass is also relatively worthless in a negative carrier. At least, I certainly can't imagine myself using anything that crude.

 

[AgX]

13 different versions... I am amazed. Maybe one day you'll post your findings down in detail.

(The belgian sheet-glass industry was leader in Europe, since floatglass being invented there.)

 

[ced]

I too remember the talc (could have been ground marble dust made by a company in the states Rutherford) also L'Oreal "Elnett" hairspray was used to do battle with NR.

 

[Billy Axeman]

Using talc to prevent newton rings is an intriguing method. I inspected some of it with a loupe and it is very fine indeed, it's more dust than grains.
It would be nice if someone here on Photrio could tell us how to use it.

There are two things that come to mind:

Using the talc would 'pollute' the film and the film holder. So there must be a good way to remove it after use.
I also wonder if this method is usable for film-holders that feed through the film from the side, like the types you see as extensions on bellows systems (Pentax, Nikon, Olympus, Hasselblad, and others).

 

[jim10219]

Glass carriers are a must for me, since I do the pin registered masking thing. But I've used 2 different plain-glass carriers (stock Beseler and a Radeka setup) and never seen a Newton ring, with Acros, HP5, Delta 100, etc. - all the normal films. Maybe I've been lucky? I'm doing 16x20 and 20x24 prints, condenser enlarger.

You must be! You live in Dallas, which isn't that far from me (OKC) and the weather is pretty similar. In the winter, I usually don't have to worry about it too much. But in the spring, summer, and fall the humidity from the gulf is high enough to cause great pain. Then again, if you're AC does a good job of removing the moisture from the air, then that might help explain why. All I know is Newton rings were my archenemy for a few years when I first got into photography. For me, one solution didn't fix it all. But now that I've got my processes down, I don't really have to worry about them.

 

[1kgcoffee]

Thanks for the very informative responses.

The warping and ease of scratching is off-putting and something I had not thought about. I have sunglasses made of polycarbonate with an anti-scratch coating that seem to hold up well. Perhaps there are products out there... I'll have to do some experimentation and report back here if I find anything else.

I'm guessing by your research, Drew Wiley there isn't much better than AN glass, which is why I snagged a bunch of 6x6 AN slide mounts for a good price. Only concern is the shrinking supply.