OPTICAL SPATIAL FREQUENCY FILTER

PROBLEM TO BE SOLVED: To reduce the focus displacement amount on the diagonal of a screen and to restrain the image quality from being deteriorated at the peripheral part of the screen by selecting the combination of the refractive index and the thickness of a double refraction plate to satisfy a specified condition when the refractive index and the thickness of two double refraction plates used for a spatial frequency filter are the same. SOLUTION: This filter is provided with a 1st double refraction plate 11 for separating incident light into two light beams spatially divided in a 1st direction and a 2nd double refraction plate 12 for separating the two light beams emitted from a phase difference plate 13 into the two light beams spatially divided in a 2nd direction different from the 1st direction. A material having the combination of the refractive index n1 and the thickness t1 satisfying a specified conditional expression in accordance with the pixel pitch of an imaging device 35, a distance between the exit pupil position of a photographing lens 10 and the image pickup surface 35p of the device 35 and the image area size of the device 35 is used as the material of the plates 11 and 12 constituting the spatial frequency filter SF.