An undesirable optical effect found on photographic films—such as transparencies mounted on a scanner drum or film in a glass contact frame—characterized by irregularly-shaped rings of color surrounding a transparent center. This phenomenon was first described by Sir Isaac Newton (hence its name) when he attempted to reproduce the colors of the spectrum by laying a thin convex glass lens on a pane of glass and shining a white light on it. The point of direct contact by the beam of light was uncolored, but surrounding the "blank" spot were rings of colors, such as a ring of blue, followed by a ring of white, followed by orange, red, violet, blue, and green. Although Newton didn't know it at the time (he didn't agree with Dutch physicist Christian Huygens that light could be described in terms of waves), these rings were caused by interference effects, caused by the light as it is refracted from the various surfaces of the lens. It is essentially the same principle as that underlying a prism. This phenomenon occurs in photographic film when the transparency or other type of film is not pressed tightly against a transparent screen.