| 摘要 |
PURPOSE:To prevent the deterioration in performance due to temp. change when a plastic lens is used for an image forming lens, etc. CONSTITUTION:A laser beam L1 generated from a semiconductor laser 1 is collimated by a collimator lens 2, and is linearly converged on a reflection surface of a rotary polygon mirror P1 by a correcting cylinder lens 5 consisting of a diverging plastic lens and the cylinder lens 3 made of glass to form an image on the surface of a rotary drum D1 through an image forming lens 4. The image forming lens 4 is a converging plastic lens, and though its convergence power is lowered due to temp. rise, since the divergence power of the correcting cylinder lens 5 is lowered also, no image forming position on the rotary drum D1 is changed, and out of focus due to the temp. rise is prevented. |
