| 摘要 |
PURPOSE:To cut off light according to the tilt angle of a transparent substrate to an optical axis and to vary the attenuation quantity of an incident light beam by making light incident on the transparent part provided to opposite parts of a transparent substrate which has an attenuation film formed on both surfaces and varying the tilt angle. CONSTITUTION:The opposite parts 102 of both surfaces of the substrate 100 which has attenuation films 101 formed on both surfaces are made transparent, the light is made incident on the transparent parts 102, and the tilt angle thetaof the substrate to the optical axis is varied. The substrate 11 is held normally at right angles to the incident light beam 14 in a state the attenuation quantity is minimum. In this state, the incident light beam 14 is transmitted through the transparent part 13 and not attenuated. Further, the substrate 11 is held at some tilt angle to the incident light beam 14 in a state of an optional quantity of attenuation. In this state, a projection light beam 15 decreases gradually by rotating an attenuation plate around the optical axis and the quantity of attenuation of the incident light beam is varied continuously over a wide range. |
