Newton's rings

Definition: Pattern or series of rings or bands seen when e.g. film is placed on glass or two sheets of glass are placed together. * Caused by interference between light waves reflected from the surfaces together with the contribution of refraction by the thin layer of air of varying thickness trapped between the two surfaces. * An optical phenomenon that is destructive of image quality in scanning when film is placed on a glass surface. * Used to check flatness or goodness of fit to a test glass in optical manufacture. Measures for busting the ring If you try to reduce Newton's rings by squeezing the film closer to the glass the problem only gets worse. The best is to use anti-Newton glass which has been treated to a polished kind of dimpling that optical scientists call 'orange peel' -- a microscopic version of the wrinkly glass in bathrooms. Some people recommend warming the whole thing with a hair-dryer to dry out the film. Hmmmm. The best way is to use an oil with a refractive index between that of glass and film -- as used for drum scanning.

Related Terms: anti-Newton

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