| 摘要 |
PURPOSE:To reduce noises due to the fluctuation of the air in an optical path by providing wind protecting pipes in a manner to allow optical axes between a first ftheta lens and a beam splitter and between a second ftheta lens and a prism mirror to pass therethrough. CONSTITUTION:This measuring apparatus detects the position of a light beam to measure the surface inclination of a polygon scanner. In this measuring apparatus, plastic pipes 5a, 5b (e.g., having the outer diameter of about 18.1mm and the inner diameter of about 13.5mm) or metallic pipes 5a, 5b are provided in optical pathes between an ftheta lens 4a and a prism mirror 8a and an ftheta lens 4b and a beam splitter 6, respectively. The air outside the pipes 5a, 5b are shut from the air where light beams L2, L3 pass, whereby noises resulting from the fluctuation of the air can be reduced, assuring highly accurate measure ment. If the inner shape of the pipes 5a, 5b in a longitudinal direction is like waves, the irregular reflection of the light beam scanned by a polygon scanner 3 within the pipes 5a, 5b can be prevented. |
