| 摘要 |
PROBLEM TO BE SOLVED: To provide a scanning optical system which can be formed compact and is capable of sufficiently reducing a beam diameter on a scanning surface.SOLUTION: A scanning optical system includes: a galvano-mirror (shown as a mirror 4a in the figure) for reflectively deflecting a light beam emitted from a light source; and an f&thetas; lens for focusing the deflected laser beam onto a scanning surface. The f&thetas; lens comprises a first lens L1 which is a spherical lens having a positive refractive power, a second lens L2 which is a spherical lens having a negative refractive power, a third lens L3 which is a spherical lens having a negative refractive power, and a fourth lens L4 which is a spherical lens having a positive refractive power, arranged in order from the galvano-mirror side. A focal length f of the entire f&thetas; lens system and a focal length f1 of the first lens L1 satisfy following conditional expression of 2.529≤f/f1≤8.437 (1). |
