| 摘要 |
PROBLEM TO BE SOLVED: To reduce fluctuation in an image forming point due to the fluctuation in an environmental temp. of a scan optical system of an oblique incident system by specifying a position of an attaching surface of a plastic lens (fθlens) for a holder holding the plastic lens. SOLUTION: The attaching surface of the fθlens 1A is joined to the attaching surface 13A of the holder on a side opposite to an optical axis 11A side for an incident position of incident light (P-RA) from a light deflector 3. The attaching surfaces 12A and 13A of this lens 1A are parallel to the optical axis 11A of the lens 1A also. Thus, when the environmental temp. rises, the lens 1A is expanded like the fθlens 1A' shown by a broken line, and the optical axis 11A is made parallel eccentric to the 11A'. On the other hand, when the environmental temp. rises, the refractive index of the lens 1A is reduced, and since the power is reduced, though a declination from the incident light (P-RA) to outgoing light (RA'-QA) is reduced, the outgoing light can keep nearly its optical path by the parallel eccentricity of this optical axis 11A, and the movement of the image forming point QA is reduced.
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