| 摘要 |
PURPOSE:To obtain an always excellent low pass effect by arranging optical low pass filters between a test pattern and a projection lens and arranging an optical low pass filter included in the optical low pass filters and comprising at least one double refraction plate to a position closest to the projection lens. CONSTITUTION:An optical low pass filter LHn employing at least one double refraction plate is provided to a position closest to a projecting lens of optical low pass filters LH and the direction of ray separation of the optical low pass filter LHn is selected to a direction at an angle of 45 deg. to the horizontal scanning line direction of an image pickup element. A test pattern projection system forms a pattern image on each image pickup face through an image pickup lens 4 and a relay post-stage group R, and a pitch PTS of dots of a gray scale and a scanning pitch P are made nearly equal in the projecting lens whose projection magnification is made variable. Since a false signal is generated to an image having a high space frequency component, the optical low pass filters LH are designed to have a thickness to eliminate (cut-off) such the high space frequency component. |
