Bob - I've done a lot of work and experimenting with this stuff and I have seen no difference in print quality between the best glass I used (Schneider nano-MRC in a 35mm carrier), the presumably cheap glass that originally came with my Saunders carriers, the glass in my Inglis carrier, and everything in between (all sorts of sample glasses from Tru-Vue, samples from Schneider's cinema division, Schott). I'm talking about the piece below the negative and above the negative. The main difference I found was in the increased transmittance of the coated glasses (due mostly to less reflection), which actually made a small difference in exposure times. "On paper", one would assume coated glass to also result in slightly higher contrast due to the reduction of reflection and flare in the system. But I'm not sure I could see a difference.
Assuming the glass in the carrier is optical glass, optically flat, and free of blemishes, scratches etc it should be fine. The only real benefit of super-hard coatings like Schneider's MRC coating is resistance to dirt and especially scratching - ie very easy to clean the carrier glass and keep it free of even the finest scratches. Worth hundreds of extra dollars? Perhaps below the negative, perhaps not. The other nice thing about using custom glass - specifically above the negative in this case - is I could use thicker glass (say 3mm for example), which results in any dust settling on the glass being out of focus. Again, a very minor benefit at least for me since I don't have a lot of dust problems in the first place.
The primary reason for my experiments with coated glass was to attempt to reduce/eliminate the occurrences of Newton rings above the negative (and occasionally even below the negative with films like TMAX and Acros which have shiny emulsions) without having to use anti-Newton ring glass, which can occasionally cause texture problems. I also thought it might help make masking a little easier. In the end while some coatings appeared to reduce the occurrences of the rings, I found no conclusive evidence any of the various coatings and multicoatings made a real difference when it comes to Newton rings. In fact I found it even more useful to give the glass a quick wipe-down with alcohol just before sandwiching the negative.
The only sure solution to Newton rings when they occur is a surface with slight "tooth" such as that of good quality anti-Newton ring glass, anti-reflection framing glass (Tru-Vue, etc), Drew's mylar suggestion - provided it is very uniform, or my solution - a simple sheet of unexposed, fully fixed Tri-X 320 (TXP). Well, actually there is one more potential experiment - Nikon's Nano Crystal Coating - but Nikon told me to get lost when I asked them about it.
I've gone all over the map with this, including correspondance with John Sexton (who is always interested in anti-Newton strategies for the emulsion side of TMX) and John Wimberley. John Wimberley does use coated glass in his carrier and feels it is necessary and makes a difference.
The caveat here is I don't make huge prints. I don't enlarge 35mm to more than 8"x10", and even my prints from 4x5 film are on 8x10 or 11x14 paper. People making much bigger enlargements might want to experiment for themselves, but these are expensive experiments - especially with sheet film sizes.
Last edited by Michael R 1974; 11-08-2012 at 08:50 AM. Click to view previous post history.