Patent ID: 6650410
Filing Date: 2003-11-18
Classification: G01N,G02F

Abstract:
An apparatus for checking a film for optical defects, comprising:a pair of polarizers placed on opposite sides of a film surface of a film to be checked with respect to said optical defects, said polarizers being parallel to the film; an illumination light source placed outside said pair of polarizers, said illumination light source projecting light onto the film through a first polarizer of said pair of polarizers; a light receiving unit placed outside said pair of polarizers and opposite from a fixed position of said illumination light source, said light receiving unit receiving light transmitted through a second polarizer of said polarizers; and a correction film having substantially birefringent characteristics identical to birefringent characteristics of a portion of the film having no optical defects, a direction in which said correction film is to be positioned being previously set according to the birefringent characteristics of the film, said correction film being placed in one of two spaces between said pair of polarizers and the film parallel to the film, wherein a luminance signal of light transmitted through the film, said correction film and said pair of polarizers is obtained by said light receiving unit to check the film for optical defects.