Anti-Newton glass

Discussion in 'Enlarging' started by David A. Goldfarb, Apr 21, 2003.

  1. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I looked again at the postcards I sent out yesterday and noticed that they had Newton's rings along the top edge! Grrrrr....

    I supposedly have anti-Newton glass in my neg carrier, but maybe it's in wrong. Ideally, the top glass should be anti-Newtonic, and the bottom should be plain glass. Anyone know how to identify the anti-Newton glass and tell which is the anti-Newtonian side, or are both sides typically anti-Newtonified?
     
  2. Donald Miller

    Donald Miller Member

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    David,
    Depending on the anti newton glass that you have, if you have the ability to determine a textured surface on the glass then it should be next to the negative.
     
  3. Thilo Schmid

    Thilo Schmid Member

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    David,

    this is easy to determine. Watch the reflections on the surface (e.g. against a window). The normal side reflects like a mirror, the Anti-Newton side has a dull reflection.
     
  4. inthedark

    inthedark Member

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    Another solution to anti newton glass which I use because my cameras have glass vacuum backs specially designed to avoid the double layer of glass in usual enlargers but not with the anti newton glass. . . A piece of mylar works great. Apply under behind negative with textured side toward the negative. The exposure will need a bit of increase as the mylar is not clear and will dampen the light a touch. I use this even when enlarging 3500% with no negative effects on focus or sharpness so long as there are no scratches on the mylar.
     
  5. fhovie

    fhovie Subscriber

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    I don't understand. If the diffusion is between the light source and the negative, that will cause the light to be more diffuse and (Callier effect) will cause a drop in contrast and reduction in edge effects (apparent sharpness.) If the diffusion is between the negative and the lens and the focus point is the emulsion side of the negative, how can this not cause some softening of the image? I am a strong believer in glass neg carriers and I only get Newton rings if I have dust. I assume it is anti Newton glass - I will need to look at it closely based on this thread. I am confused about the use of Mylar though.
    Frank
     
  6. Thilo Schmid

    Thilo Schmid Member

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    Frank,
    Newton Rings are based on light inference between the glass and the negative. They can only appear, if there is a tiny air space between the glass and the negative. If the surface of either the negative or the glass is not absolutely smooth, the air between the glass and the negative can escape and both get into real contact. The emulsion side of the negative is usually not very smooth. So Newton Rings may not appear on this side.

    The structure of an Anti Newton Glass or of a Mylar (or other diffusion material) is usually not rendered below mag-ratios of ~25x. However, they reduce contrast transfer in theory when the diffusion is between the neg and the lens.

    Any diffusion above the neg may change the light characteristics in case of a condensor head. But did you really experience any Callier Effect with your negatives? IMO, this requires point light sources and super fine emulsions to really matter. I did not find any non-linear difference between my diffuse/diffuse densitometer and my lab mether below the condensor head. A diffusion may change contrast transfer, but I would not expect any non-linear changes here.