| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical scanner and an image forming apparatus, having wide effective writing width and a high uniform speed characteristic on the surface to be scanned by using a deflection mirror under sine wave oscillation. SOLUTION: The optical scanner has a light source 1, a deflection mirror 5 for deflecting and deflecting a beam from the light source 1 by using sine wave oscillation and optical scanning elements 6, 7 for scanning the surface to be scanned with the deflected and reflected beam at an almost uniform speed and satisfies the following conditional expression 0.4<ϕmax/ϕ0<0.9/[20/ϕ0) (1/4)], whereϕ0 is the amplitude angle ( deg.) of the sine wave oscillation of the deflection mirror 5 andϕmax is the maximum rotation angle ( deg.) of the deflection mirror 5 corresponding to effective writing width. Another mirror may be arranged opposite to the deflection mirror 5, so as to reflect the beam from the light source 1 a plurality number of times.
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