Anti-Newton Glass

Discussion in 'Enlarging' started by Jim Chinn, Nov 10, 2003.

  1. Jim Chinn

    Jim Chinn Member

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    I have recently been asked to make contacts and then enlargements of some negatives from the late 1920s/early30s. The negative material is very thin and prone to curling. I will need to manufacture a carrier for the negatives and incorporate glass to keep them flat.

    I have never enlarged with glass carriers, and so even though I have heard of newton rings and anti-newton glass I need some info on what causes newton rings and what makes the glass special. I do contact print large negatives with a glass plate, but have never had a problem. I assume that it has something to do with the glass changing the light path before it reaches the lens, causing some sort of aberation.

    Is there a retail source for the glass? It does not have to be exact size, if the size is larger then what my carrier requires I can have it cut down here.

    Finally, I think I have heard of an anti-newton glass cleaner, or spray or some such thing. Anyone familiar with this product or if it works?
     
  2. Donald Miller

    Donald Miller Member

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    Jim,
    I have always heard that Newton rings are caused by entrapment of moisture between the negative and glass. Anti newton glass on my glass carriers is a glass with a slight texture and not a "coating". I have heard that Focal Point is one source for anti newton glass. Insofar as a cleaner, I just use a typical glass cleaner.
     
  3. Leon

    Leon Member

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    Tetenal make an Anti-Newton Rings spray - maybe that is what you mean? I havent used it but plan to on a glass carrier in a 4x5 enlarger i have recently bought. I assume that it adds a textured coating to the glass?
     
  4. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    You might find that it's not a problem, so you could try conventional glass before ordering anti-Newton glass. Whether you get Newton's rings will depend on the surface of the film and factors like humidity.

    Some AN glass is textured to prevent contact between two smooth surfaces, and some is coated with an anti-reflection coating like that used on lenses to reduce reflections between the two surfaces that are the cause of Newton's rings.

    There is a spray, but I believe it is supposed to be sprayed on the negative rather than the glass, and it's messy to clean up. Another such approach I've heard of is to use a dusting of fine talc or cornstarch on the base side of the neg (Newton's rings don't usually form on the emulsion side).

    Another source for AN glass is stephenshuart.com
     
  5. Ole

    Ole Moderator Staff Member Moderator

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    Newton rings are a result of almost full contact betwen two smooth surfaces. The distance between the two surfaces must be of the same order of magnitude as the wavelength of light! When light is reflected between the two surfaces, some of it will be half a wavlength (or one and a half, or two and a half...) out of step with that passing directly through. This had the same result as absorbing a little of the light.

    The distance between film and glass, especially around a speck of dust, will vary from practically zero to a number of wavelengths. In between, all colours of light will be "extinguished" at some point. This is what gives Newton rings.

    It does not depend on humidity, but on the "shinyness" of the surfaces.

    So the two ways to combat it are: A: Increase the distance, or B: Increase the roughness.

    Simple, innit?
     
  6. RAP

    RAP Member

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    Jim,

    Sounds like these negatives may be valuable. I would be very leary about glass carriers. The emulsion may stick to the glass. Zone VI sells a negative carrier thru Calumet, that may be just what you need.

    "4x5 Out-Straight Type 2 Negative Carrier"

    Catalogue # EN57455

    Designed for large format photographers who require ultimate precision of focus, the Out-Straight negative carrier will draw your negatives perfectly flat. It is also adjustable in negative size to accommodate the larger film pack and Polaroid negatives.
     
  7. chrisl

    chrisl Member

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    Guys, I got a glass 4x5 negative carrier w. my D5 enlarger. In fact, it looks like this one I found on Ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2968810635&category=29987

    Not sure if it's AN glass or not, but it does look identical, and the edge of one of the glass sheets is 45deg tapered cut. Is this AN glass?? How perfect does the glass have to be? It has no scratches that I can see, but it does have just a few, very small specs that wont' come off in cleaning. So just trying to get an idea if this is usable. Also, is using a glassed neg. carrier Mandatory for flat negatives=sharp prints?? I certainly cannot afford a new carrier from Calumet above ($200).

    thx
    chris
     
  8. Donald Miller

    Donald Miller Member

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    Chris,
    Anti Newton glass will have a faint texture to it. On my negative holder one of the sheets of glass is AN and the other is optical glass. I believe my AN sheet is on top of the negative ( I would need to check to be sure). Insofar as the quality of the glass and blemishes, the blemishes may be apparent on the image and they may not be. It depends on how large they are and how large you are enlarging your negative. At the very worst they should be a light or white spot on the print and should be such that spotting the print would make them disappear. A glass carrier will be of increasing importance as the size of negative increases. I have used a glass less negative carrier on an old D2 4X5 for a number of years. However my new enlarger gives me noticeably sharper results. I don't know whether that is entirely the result of the glass neg carrier or a combination of better alignment, better lens, and the neg carrier.
     
  9. marcello.brussard

    marcello.brussard Member

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    I agree with Ole,
    Newton's rings are interference figures created by the reflection of light between film and glass. Film with a very smooth surface are more prone to this kind of problems. Umidity is an issue because the film absorbs the moisture and changes its surfaces (hardness and smoothness). This is what appen to me: Ilford Delta 100 is a very smooth film, but I usually get newtons ring only during the summer or when the eath is on (i.e. when the umidity in my house increases). There are a number of different products to solve the problem (glass, spray, powders), but the principles are just two: 1) avoid to have glass and film surface running parallel; 2) modify the distance between film and glass.
    Since the interference is limited to the support side of the film (the emulsion side is irregular, the support side is smooth), I use to put a very thin frame of black cardboard between film and upper glass. Simple, clean and very cheap.
    Ciao,

    Marcello
     
  10. chrisl

    chrisl Member

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    Thanks guys. I must have the non AN glass as neither the top or bottom glass has any texture to it.

    I found some more information and other options over on dursts webpage:

    http://durst-pro-usa.com/neg_glass.htm
    And a couple interesting statements:

    -We still offer the old type AN (Anti Newton) glass for those customers who print with COLD LIGHT and DIFFUSED LIGHT sources. But would like to point out that AN glass deteriorates sharpness considerably. The rate of deterioration is so considerable that Durst Auto Focus enlargers can not be programmed for correct focus using Anti Newton Glass
    -The new AR glass will also suppress Newton rings.

    -Also the trend is that Fine Art printers now are using a glass less mask on top of the negative and only glass at the bottom.

    So, replacing the glass is an option...or try the mask technique as noted above as top layer.

    Anyway, alot more confusing than I would've thought regarding keeping a large 4x5 neg. flat for enlarging.

    Chris

    ps anyone know the website of Omega enlargers? I thought it was simmons omega, but can't find the company's webpage and Ive been there before! geesh.
     
  11. Ole

    Ole Moderator Staff Member Moderator

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    A very good anti-reflex coating should also work as AN-device. After all, the rings are formed by reflection between two not-quite-touching surfaces. An anti-reflex coating half a wavelength thick should do the trick.
     
  12. Nacio Jan Brown

    Nacio Jan Brown Member

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    I replaced the top piece of glass in my negative carrier with something called "Denglass" (sp?) that I got from a picture framer. I forget where I got this tip. It has been 100% effective. Newton rings show up as a problem where the film base side of the negative is in close proximity to the glass, as described above. njb