Method of and apparatus for measuring optical distortion

An apparatus for measuring optical distortion of measured material which comprises:

• a background screen (2) disposed in rear of a measured material (1) having light transmission properties, and having a regular pattern (3) composed of triangle-wave-like unit patterns (3a) each extending continuously in a predetermined direction, which are arranged at distances of equal pitch,
• an image pick-up device (4) capable of line-scanning which is disposed in front of the measured material (1),
• a measurement range control means (5) to move at least one of the measured material (1), the image pick-up device (4) and the background screen (2) and to take a picture of the background screen (2) through the measured material (1) by successively line-scanning the entirety of a range to be measured of the measured material (1) with the image pick-up device (4),
• a pattern change point detection means (6) to detect change points of the regular pattern (3) of the background screen (2) by the line-scanning of the image pick-up device (4),
• a pattern segment extracting means (7) to extract pattern segments of the triangle-wave-like unit patterns (3a) on the basis of the pattern change points detected by the pattern change point detection means (6),
• a characteristic point operating means (8) to operate characteristic points from the pattern segments extracted by the pattern segment extracting means (7),
• a reference characteristic point storing means (9) to previously store coordinates of characteristic point obtained by photographing the background screen without interposing the measured material (1), and
• a distortion evaluating means (10) to evaluate the optical distortion of the measured material (1) by comparing coordinates of characteristic point obtained by interposing the measured material operated by the characteristic point operating means (8) with the coordinates of characteristic point in the reference characteristic point storing means (9).