Just like any other optical system, esp like a view camera. If you have a bunch of flare inside your
enlarger bellows etc, then optically coated glass might help. But if your system is quite black inside,
without light bouncing around, you just need good flat glass. I've tested em all, believe me.
Just curious Michael, what was the approximate cost of the 4x5 glass?
Originally Posted by Michael R 1974
Patrick, it was a while back but I've got it here somewhere. Will check.
The glass in the carrier becomes part of the optical system. Although it is not in focus, irregularities do affect the image. This is why AN glass can be such a problem. The best quality stuff seems to work decently, but there is a lot of inferior stuff out there that definitely degrades the image. I've generally managed to do without it. For the plain glass, window glass is out. Good quality float glass seems to be OK, but it is certainly not top optical quality. You can get optical flats which are excellent. They come in various qualities from what is essentially selected float glass (moderately expensive) to tenth wave flatness and better (very expensive).
At one time, about a decade ago, only about 1% of float glass was suitably flat for optically coating
by the pioneers on non-optical applications, like Denglas. Now that optical coating has become available for low-e window use, productivity of suitable product has increased. But it's still inferior
to plano-corrected real enlarger glass. The specific anti-Newton pattern is critical, and will even work on both sides of the film in certain applications. But you need to test all the variables, including
film type, degree of magnification, kind of diffusion in the enlrgr head, specific enlarger lenses and working f-stops, etc. At the moment, each enlarger I have has a different kind of glass in it, or a
different set of options, because each is dedicated to a different use (different formats, color vs
b&w film, scale of magnification, etc).
Although a fan of glassless carriers, I thought this little film of a master French printer quite interesting and I note she uses a glass carrier. The way she wipes the negatives with her fingers is indicative of the way we all have our own procedures when printing.
Agree it goes to show there is definitely more than one way to do things. I'd NEVER wipe my negatives like that. Actually I don't even handle them without gloves. But it seems to work fine for the printer in the video.