I wanted to update this thread with some preliminary results of a couple of experiments with optical glass for enlarging carriers. Appreciate any feedback, suggestions for other types of glass, etc.
Just to recap, I had been thinking about full glass carriers in which we have glass below the negative, and why we usually don't think about the quality of the glass. Further, would it be possible to reduce or eliminate the intermittent problem of Newton Rings in enlarging and contact printing by using coated glass. This would be nice for two reasons: a) It would reduce/eliminate the need to use sometimes problematic etched anti-Newton ring glass above the negative, b) it could help prevent Newton rings from forming on the emulsion side of certain films such as the TMax films which have a glossy emulsion surface. I wanted to try several different types of anti-reflection coatings.
Experiment 1 involved replacing both the top and bottom glasses in a 35mm carrier with 2mm clear, multi- resistant-coated ("MRC") optical filter glass from Schneider's top-line B+W filters. As expected, light transmission was improved (who cares really), and the extremely hard MRC coating is a breeze to keep clean and very resistant to scratching. Unfortunately Newton rings are not eliminated – even on the emulsion side of TMax and Fuji Acros, but they do seem to be significantly lessened. The major downside is the price of this glass, even for a 35mm carrier. Also, the MRC glass is not available large enough to accommodate anything bigger than a square medium format negative.
Experiment 2 involved replacing both the top and bottom glasses in a 4x5 carrier with 3mm clear, coated optical filter glass from Schneider’s Motion Picture division (they custom cut and bevel filters for movie/TV cameras etc so they can make larger sizes). The anti-reflection optical coating is different than MRC. The results seemed to be the same as in experiment 1, although this glass is not quite as expensive, and is also available in different thicknesses.
Experiment 3 was the same as experiment 2 but using Miroguard anti-reflection coated framing glass from Schott. Same results.
Awaiting receipt of anti-reflection and anti-glare framing glasses from Tru-Vue. I am curious to try their coated glass. I am also interested in potentially using the anti-glare glass on top of the negative either in enlarging or contact printing. The anti-glare glass has a slightly roughened surface. The effect should be similar to etched anti-Newton ring glass, but perhaps the texture will be finer, which could potentially be less problematic than with some anti-Newton ring glasses, where a faint texture can sometimes be visible in smooth tonal areas of the print. If the “texture” is fine enough, it might also prove useful in some condenser enlargers. I’ll have to get some Focal Point anti-Newton ring glass to use as a reference point. Framing glass is much less expensive than optical filter glass.
There are scattered reports of specific anti-Newton ring coatings (mostly in the world of touch panels etc, but also optics). That would be fun to investigate.
In addition, one would think a “nano-particle”-type optical coating (such as Nikon’s Nano Crystal Coat, and some other coatings I’ve read about) could be useful in reducing or eliminating Newton rings.
For now though, the only solution which seems to work all the time, is simply placing a fixed (clear) sheet of Tri-X 320 between the top glass and the negative. This is great for contact printing too, and eliminates the need for anti-Newton ring glass above the negative.
The more vexing problem remains underneath the negative in an enlarging carrier, with films like TMax that have shiny emulsions. I have been corresponding with John Sexton on this over the past several months as it turns out he has been intermittently performing similar anti-Newton ring experiments with TMax . I will pass on any results (although for now he’s paused on these tests since he’s currently not getting Newton rings). Indeed, I have also found Newton rings to be an intermittent problem, which makes it that much more difficult to solve.