摘要 |
PROBLEM TO BE SOLVED: To provide a multibeam scanner which never has an out-of-focus scanning position even when the scanner has curvature of field aberration in a multibeam scanner which has plural light emission points. SOLUTION: The image-side NA of an optical system is so set that a range de-ΔS of overlaying of depth de of focus at photosensitive body surface positions corresponding to light emission points ch1 and ch2 of the multibeam scanner is positive, preferably, the value obtained by subtracting a field curvature aberration quantity Cf from the overlaying range de-ΔS is positive, where de is the depth of focus to the two light emission points ch1 and ch2 andΔS is the interval quantity between the light emission points ch1 and ch2 in the direction of the depth of focus.
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