| 摘要 |
PROBLEM TO BE SOLVED: To reduce noises when a rotary polygon mirror is rotated. SOLUTION: The rotary polygon mirror 3 is surrounded by a sound-proof case 10a, of which one part of the side wall of an optical box 10 is made thick, and between the rotary polygon mirror 3 and an image forming lens system 4, a multiplex transmission window composed of two pieces of dust-proof glass 11a and 11b is provided. This window is provided for remarkably attenuating the noises of the rotary polygon mirror 3 through two pieces of dust-proof glass 11a and 11b and a spatial part 11c between them and further, by making one piece of dust-proof glass 11b thick, noise cutting property equal with a sound-proof case 10a can be provided. |
