Can it be a solution for avoiding newton rings

[Hugo Zhang]

Drew,

What is your experience of putting a sheet of Mylar between the glass the negative?

Thanks.

[Bob Salomon]

Drew,

What is your experience of putting a sheet of Mylar between the glass the negative?

Thanks.

Newton rings are formed when one smooth surface, like the base side of film, comes in contact with another smooth surface.

Get AN glass and save time and money with things that can deteriorate image quality and not work.

[Bob Salomon]

Drew,

What is your experience of putting a sheet of Mylar between the glass the negative?

Thanks.

Newton rings are formed when one smooth surface, like the base side of film, comes in contact with another smooth surface.

Get AN glass and save time and money with things that can deteriorate image quality and not work.

[Ron_in_Alaska]

I have used a ground glass for contact printing color Cirkut negatives for years some are over 7 feet long. NO Newtons rings period. I ground the glass myself with carborundum. This doesn't affect the sharpness of the image either. Grinding glass is simple and fairly fast. The grit is from a lapidary supply and is very cheap.

[Eric Woodbury]

Bob, it takes both the closely spaced surfaces AND some degree of coherent light. This is why even a polished diffuse surface in contact with negative will NOT produce Newton's rings.

[Bernard_L]

Bob, it takes both the closely spaced surfaces AND some degree of coherent light. This is why even a polished diffuse surface in contact with negative will NOT produce Newton's rings.

The degree of coherence (i.e. small effective wavelength range) required to display interferences is directly related to the difference in path length between the interfering paths. The longer the path length, the smaller the wavelength range needs to be in order to display interference fringes. In the case of Newton rings, the surfaces are at or near contact, i.e. in physics jargon, near the white fringe (not coincidentally named so because interference fringes are visible even in "white" light when the path difference is close to zero).

Displaying interference fringes requires close contact OR (not AND) highly coherent light. With a laser, even my little sister can show fringes all over the room.

The reason(s) a diffuse surface, even in contact with a negative will not show Newton rings, are that:
(a) most of the surface is a few microns away from the negative; negligibly small in terms of negative flatness, but already "far" in the context of a wavelength range spanning 100 or 200 nanometers (low coherence)
(b) at/near those spots where the glass is actually touching the negative (doing its job of keeping it in a plane) the spacing varies from zero to one or more micrometers over a lateral distance of a few microns; over that distance, the Newton rings are present, but so closely spaced as being effectively invisible.

[Drew Wiley]

Hi Hugo. Mylar can certainly work, depending, but only on the upper side of a negative carrier or backside of the original neg between it and a contract frame glass. I use 5-mil mylar and sometimes 3-mil mylar FROSTED BOTH SIDES for masking and other contact printing scenarios. You buy a big sheet or two of it and put it over a lightbox to spot any blemishes, then cut down into the smaller sizes you need. You'll discover there's a slight linear grain a particular direction, and should orient the mylar the specific direction that will least affect something like open featureless skies. And it is important to use true mylar. It comes is different brand names, but should be distinguished from frosted or textured acetate, which has a much more perceptible pattern in any samples I've tested, and is not dimensionally stable like mylar. Clear textured mylar would be a trickier proposition, but one could hypothetically fix out a sheet of Arista Ortho Litho film stock, which is textured, and try that. The problem is more complex than certain foregoing posts would make it seem. I once had samples of 13 different kinds of AN surfaces in stock for testing. It can depend on the angle of incidence of the light, the degree of magnification relative to format size, ambient humidity, and especially on a high amount of contrast increase like using the highest grade on VC paper. I don't believe there's such a thing as a silver bullet that works best in every situation. Personal testing is mandatory.

[Peter De Smidt]

P99 acylic works well if heat isn't involved.

[Drew Wiley]

Nonglare acrylic sheet isn't stable. It bows toward the light side. It also is affected by long-term humidity changes. The biggest problem is that acrylic is so damn electrostatic, a dust magnet. There are antistatic cleaners that reduce that somewhat. I have a LOT of experience with this material. But it might indeed be a realistic answer under a cold light if the overall size is modest. I should probably try it in my own 8x10 cold light system, but currently have something relatively exotic for that.

[Barry Kirsten]

A few days ago I was thinking about Newton rings and wondering why I never get them. I think the answer is that I've been using the same sheet of 6mm thick glass for decades and in that time it's developed a coating of grease from handling which gets reinforced each time I wipe it before use. Just a thought.