anti-Newton glass, how is it made?greenspun.com : LUSENET : Large format photography : One Thread
How does anti-Newton glass differ from regular glass in the way it is manufactured? Does it have an uneven or patterned surface to prevent the formation of Newton rings? Would this pattern be visible in contact printing one negative onto another using anti-Newton glass in a contact frame?
-- Mark Nowaczynski (firstname.lastname@example.org), March 06, 2001
From Ron Wisner's Article on his company's page:
"In a related subject, many of you have experienced problems with the formation of Newtons rings when film comes on contact with a glass surface. This often occurs when a a negative is placed in contact with the negative carrier of an enlarger or placed in a contact printer. As described above, if the medium between the glass and the negative (air) is just the right thickness, interference will occur, resulting in the colored rings which ultimately show on the final print. If the source of the reflections which give rise to the interference rings can be removed, the rings will not be produced. This cannot be done completely, of course, but if the glass is coated the rings will be greatly reduced. If the glass receives a single layer coating, the ring intensities will be cut in half. If the glass is multi coated, which reduces the reflections to about one half a percent (from 4%), the reflections, and therefore the Newtons rings will be reduced eight fold. We have tested this with several photographers, and they report no visible Newtons rings in their final prints. I personally use a heavy piece of single-layer-coated plate glass to make all of 8x10 contact prints with no visible rings."
-- Sean yates (email@example.com), March 06, 2001.
"Does it have an uneven or patterned surface to prevent the formation of Newton rings?" Yes. "Would this pattern be visible in contact printing one negative onto another using anti-Newton glass in a contact frame?" No.
Conventional anti-Newton's ring glass has a fine pattern etched on the surface. This breaks up the pattern made by optical inteference and the varying thickness of the air gap between the photographic material and the glass. As a consequence the rings are no longer apparent. The pattern is so fine that no evidence can be seen in the image. My enlarger has a glass carrier with anti-Newton's ring glass and even under enlargement no untoward effects can be seen. If you were to see a pattern from some anti-Newton's ring glass, I would suggest returning it to the seller and obtaining some with a finer pattern.
Coated, especially multi-coated glass, is an elegant solution, but cost suggests the use of the conventional etched anti-Newton's ring glass.
-- Michael Briggs (firstname.lastname@example.org), March 07, 2001.
Sorry to report, but I do get a texture pattern in the print when I try to use anti-Newton glass for contact printing, though it works fine in the glass-sandwich carrier in my enlarger.
I use coated glass for contact printing my LF negatives, though even that is not foolproof; there are times when I get Newton rings anyway. I shoot mostly HP5+; I've been told that films with retouching surfaces, such as TXT, are less prone to Newton's rings, but haven't yet had a chance to test this myself.
-- Oren Grad (email@example.com), March 10, 2001.
I report textures too when I use AN glas on contact printing. This might be verry nice when you do hard negatives and positives of film for some effects.
-- Matthias (firstname.lastname@example.org), May 15, 2001.
Some companies etch glass to make it AN.
Some companies spray glass to make it AN.
-- Bob Salomon (email@example.com), May 16, 2001.