| 摘要 |
PURPOSE:To produce easily an f<theta> lens with two-lens constitution and to obtain it having an extremely large effective deflecting angle at a moderate price by constituting said lens of two positive meniscus lenses whose recessed parts point the deflecting point side of a beam and specifying the relationship between the curvature radius of each lens surface and a synthetic focusing distance. CONSTITUTION:Two meniscus lenses 10 and 20 share an optical axis Ax and are disposed with their recessed surfaces pointing the side of a deflecting point P. It is the center of the deflection of the beam L, which is deflected in terms of equal angle speed with the deflecting point as a center. The beam L which is made parallel flux and makes incident at an incident angle theta converges on a scanned surface S in a spot-like shape. Where the curvature radii of respective lens surfaces are sequentially assumed to be R1, R2, R3 and R4 from the side of the deflecting point P, and where the synthetic focusing distance is set to (f), they satisfy conditions of expressions. Since this f<theta> lens has the two-lens constitution, it has an extremely large effective deflecting angle near to 110 deg., and its image curvature and an f<theta> characteristic are far excellent.
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