| 摘要 |
PROBLEM TO BE SOLVED: To obtain a transmission optical system capable of realizing excellent image reproduction at high speed in a twice-incidence type optical scanner. SOLUTION: This optical scanner is provided with a light beam source, a rotary polygon mirror 4 having plural reflection surfaces reflecting and deflecting a light beam from the light beam source, the transmission optical system 22 transmitting and making the light beam reflected and deflected by the 1st reflection surface 5 of the mirror 4 incident on the 2nd reflection surface 6 of the mirror 4, and a scanning optical system forming the light beam reflected and deflected by the surface 6 as a beam spot on a surface to be scanned and making it scan the surface to be scanned. The optical system 22 constitutes an afocal optical system consisting of a front group 24 having positive refractive power and a rear group 12 having the positive refractive power in a main scanning direction, and the front group 24 of the optical system 22 consists of three single lenses 7 to 9 having positive, positive and negative refractive power in order from an incident side. |
