| 摘要 |
PURPOSE:To eliminate the need to replace a slit at every time of variable magnification and to permit one slit to deal with all variable powers, by providing a member which cuts off part of luminous flux on an optical axis near the incidence or projection end of a lens in such a direction that it crosses the slit lengthwise. CONSTITUTION:The slit 2'' over an original surface 1 is a long and thin rectangle and a light shielding member 7 in a round-rod shape is provided at a direction crossing it lengthwise. The light shielding member 7 is provided at a specific position on the optical axis 6 on the incidence side of the lens 3, but this position is so determined preferably that the member contacts the innermost light beams 8a and 8b of luminous flux incident to the incidence pupil of the lens 3 from the outermost points 1a and 1b of the original surface 1 on the optical axis 6 from the outside. Consequently, the light shielding area of the light shielding member 7 for the incidence pupil of the lens 3 at each point in the original surface 1 increases gradually from the outermost point toward the optical axis, so the illuminance in an image surface 4 does not decrease from the center part toward the peripheral part, correcting a decrease in the quantity of the peripheral light of the lens 3. |
