| 摘要 |
PROBLEM TO BE SOLVED: To provide the collimator lenses in which a provision is made for a first lens, that is faced to a parallel luminous flux side with a concaved surface, and a second lens, that has a positive refractive power and has at least one non-spherical surface, looking from the parallel luminous flux side, necessary brightness and a back focusing are secured using a simple lens constitution and an application is made for a multibeam scanning optical system having a properly compensated off-axis aberration. SOLUTION: Looking from the parallel luminous flux side, an arrangement is made for a first lens L1, which is faced to a light source side with a convex surface and is made of a positive meniscus lens, and a second lens L2 in that order. The surface of the lens L1 facing the parallel luminous flux side is made into a non-spherical surface and the collimator lenses satisfy a conditional equation of -5.90<R1/f<-0.33 where R1 is the near axis radius of curvature of the surface of the lens L1 on the parallel luminous flux side and f is the focal distance of the entire lens system.
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