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Photo Forum / Film Photography / Darkroom / March 2008AN (Anti-Newton) glass question
The Focomat IIa uses AN glass for the top glass, and plain for the lower. Is this a universal principle? IOW, can I presume the same for any two-glass carrier? > The Focomat IIa uses AN glass for the top glass, and plain for the lower. > > Is this a universal principle? IOW, can I presume the same for any two-glass > carrier? The Matte surface of the AN glass has to be above the negative.  SignatureReality is a picture perfected and never looking back. > The Focomat IIa uses AN glass for the top glass, and plain for the lower. > > Is this a universal principle? IOW, can I presume the same for any > two-glass carrier? What I have heard is that the Anit-Newton glass is against the smooth base side of the negative, and you can use plain glass against the rougher emulsion side of the negative. I don't know if this is a fact or not; I use glassless neg carriers. >> The Focomat IIa uses AN glass for the top glass, and plain for the lower. >> [quoted text clipped - 5 lines] > emulsion side of the negative. I don't know if this is a fact or not; I use > glassless neg carriers. It is more likely that the texture of the ANR glass cannot be in the emulsion focal plane without showing up (as well as the emulsion not (usually) being as glossy as the base. gr > The Focomat IIa uses AN glass for the top glass, and plain for the lower. > > Is this a universal principle? IOW, can I presume the same for any two-glass > carrier? Yes, as long as it is an anti-newton negative carrier. Plain glass carriers will have plain glass on both sides. This would be the time you would get the "newton rings" on your print around the highlights. Right? Draco On 3/19/2008 12:54 PM Draco spake thus: >> The Focomat IIa uses AN glass for the top glass, and plain for the lower. >> >> Is this a universal principle? IOW, can I presume the same for any two-glass >> carrier? > > Yes, as long as it is an anti-newton negative carrier. Your reply is a tautology. If the carrier has anti-Newton glass in it, then it's an anti-Newton negative carrier. > Plain glass carriers will have plain glass on both sides. This would > be the time you would get the "newton rings" on your print around the > highlights. I think the OP knows this. On Mar 16, 5:09 pm, <jjs> wrote: > The Focomat IIa uses AN glass for the top glass, and plain > for the lower. > > Is this a universal principle? IOW, can I presume the same > for any two-glass > carrier? Yes, as long as it is an anti-newton negative carrier. Plain glass carriers will have plain glass on both sides. This would be the time you would get the "newton rings" on your print around the highlights. Right? Draco Newton's rings are an interference pattern where two beams of light can interfer. The usual cause is reflection between two reflective surfaces that are very closely spaced. In the case of an enlarger using a glass sandwich negative holder the two surfaces are the support side of the film and the glass next to it. By making the glass slightly rough the reflection is broken up and the rings are not formed. Newton's rings can be formed on the emulsion side too but the emulsion is usually rough enough, or the amount of reflection from the gelatin low enough, so that rings are not produced there. Newton's rings appear as somewhat uneven dark and light concentric rings all over the image. They follow approximately any lack of flatness in the two surfaces involved. Newton's rings are often used to measure the degree of conformance of two closely spaced surfaces where one of them is transparent as when testing the figure of a lens against a standard. I think the effect you are referring to is halation. This is also caused by reflection, usually in film, where bright areas are reflected back into the emulsion by the support. All modern film has either a light absorptive coating on the back or in a layer under the emulsion (the usual method for color film) to eliminate halation. Halation was a very serious problem with early glass plates where it formed quite noticeable halows around bright objects and reduced the contrast of more extended bright objects. Glass plates were also coated with anti-reflective layers on the back. It is usual for the anti-halation layer to be removed mechanically (as in the Remjet used for Kodachrome and some motion picture stocks) or for the dyes it contains to be made colorless by the sulfite in the developer or fixing bath. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > Yes, as long as it is an anti-newton negative carrier. I'm glad that was brought up. Quite frankly, I just presumed the negative carrier in question would need anti-newton glass. I will describe it and perhaps someone can enlighten me. The glass is for the Saltzman 8x10 enlarger. The carrier works with two plates of glass (exactly 8x10") to sandwich the negative. There is nothing whatsoever to separate the glasses, except the negative. One removes the lower glass, does what he can to remove dust, replaces the glass, and swings four tension clips over the edges of the glass. Requires AN glass, no? Thank you all! > > Yes, as long as it is an anti-newton negative carrier. > [quoted text clipped - 10 lines] > > Thank you all! Ok for you, I just pulled my Omega 10x10 carrier out of the enlarger and it has two sheets of standard optical glass but not AN. To my knowledge AN appears with a Matte surface unlike standard optical grade glass. It (AN) will look less than perfectly clear. Imop & Perhaps Richard K. can corroborate AN is only needed with a Condenser housing, I have an Omega diffused Halogen one of three known to exist. SignatureReality is a picture perfected and never looking back. >> > Yes, as long as it is an anti-newton negative carrier. >> [quoted text clipped - 30 lines] > have an Omega diffused Halogen one of three known to > exist. Newton's rings are most obvious where the light source is collimated which is at least partially the sase when a condenser source is used. A diffusion source will not usually display the rings. Most condenser enlarger lamphouses are somewhere between diffuse and a true specular source which requires a point source as well as a means of collimation. The typical enlarging lamp is a fairly large and quite diffuse source (for instance an opal lamp) so the resulting light is partially diffuse and partly collimated. Saltzman also made a glassless negative carrier that held the negative flat by spring tension by means of clips on the carrier. --- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > Newton's rings are most obvious where the light source > is collimated which is at least partially the sase when a > condenser source is used. A diffusion source will not > usually display the rings. You just saved me $90. I owe you. Truly. The lamp housing, which was originally dual condensers, is missing, and we plan to replace it with a diffusion source. So plain optical glass it shall be. >Ok for you, I just pulled my Omega 10x10 carrier out of the enlarger >and it has two sheets of standard optical glass but not AN. To my >knowledge AN appears with a Matte surface unlike standard optical grade >glass. It (AN) will look less than perfectly clear. Imop & Perhaps >Richard K. can corroborate AN is only needed with a Condenser housing, I >have an Omega diffused Halogen one of three known to exist. No. Under some conditions -- atmospheric and of the negative -- you'll see Newton rings with this glass carrier. I know because I have one. To make one of my negatives printable I had to replace the top glass in my 10x10 Omega carrier with AN glass and the bottom glass with a piece of anti-reflective coated glass from a frame shop. With that done, the problem was considerably lessened, though not eliminated entirely. The best solution is a tension carrier like the pin-register carriers Fotar used to make for their enlargers -- actually the only 8x10" tension carriers I've ever seen. In 4x5" the Beseler Negaflat, of course, was fairly common. SignatureThor Lancelot Simon tls@rek.tjls.com "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky > >Ok for you, I just pulled my Omega 10x10 carrier out of the enlarger > >and it has two sheets of standard optical glass but not AN. To my [quoted text clipped - 15 lines] > tension carriers I've ever seen. In 4x5" the Beseler Negaflat, of > course, was fairly common. Is your 10 x10 the dichroic lamp house or a condenser? The Dichroic is a 1,000 watt quartz halogen source. My diffused halogen is half that. SignatureReality is a picture perfected and never looking back. >Is your 10 x10 the dichroic lamp house or a condenser? The Dichroic is a >1,000 watt quartz halogen source. My diffused halogen is half that. It's the dichro. Someone had put some funny low-wattage, long-life bulbs in there, though -- when one finally blew and I had to replace them all, it ran so much hotter it melted off some black contact paper which had been used to shim the assembly for light tightness! My Chromega 10x10 head is actually on a Durst Laborator 138 which was one of several adapted for use printing highway signs by a company in Toronto. It came with motorized raise/lower and focus and a 50" coiled between the motor control box and the remote control -- it's hard to imagine what it must have been like to use in that configuration. The company sold them off on eBay as they wore out and converted to Lightjet units, I believe. I got one of the earlier ones, so I probably overpaid, but it's worked well for me for about 10 years now though it has some loose bits and other quirks I would think would have made it annoying for daily commercial use. SignatureThor Lancelot Simon tls@rek.tjls.com "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky >> Yes, as long as it is an anti-newton negative carrier. > [quoted text clipped - 12 lines] > > Thank you all! Do you get Newton's rings? If so AN glass will eliminate them, if not then don't bother. BTW, I suspect glass with anti-reflection coating on it similar to a lens would accomplish the same purpose. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > Newton's rings are an interference pattern where two > beams of light can interfer. The usual cause is reflection > between two reflective surfaces that are very closely > spaced. Does a single original beam source that is split, connote two beams? If so my guess is that, Propagation seems to be the correct term? SignatureReality is a picture perfected and never looking back. |
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