Optical scanning apparatus and image forming apparatus using the same

An optical scanning apparatus, comprising:

• a light source unit;
• a deflection unit for deflecting a light beam (Ray1) emitted from the light source unit for scanning;
• and
• an imaging optical system for imaging, on a surface to be scanned, the light beam (Ray1) deflected by a deflecting surface of the deflection unit,
• wherein the imaging optical system comprises, in an optical path in the following order from a side of the deflection unit:
• an imaging optical element (G1);
• a first reflecting mirror (M1);
• and
• a second reflecting mirror (M2),
• wherein the second reflecting minor (M2) is disposed, within a sub-scanning section, between the deflection unit and the imaging optical element (G1) in a direction of an optical axis of the imaging optical system, and
• wherein the second reflecting minor (M2) and the imaging optical element (G1) overlap each other in a sub-scanning direction within the sub-scanning section, and the following conditional expression (1) is satisfied:
• A
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• TAN
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• [
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• 0.55
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• h
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• L
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• tan
• ⁡
• (
• α
• )
• -
• σ
• }
• L
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• 2
• -
• L
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• ⁢
• 1
• ]
• <
• θ
• <
• A
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• ⁢
• TAN
• ⁡
• [
• {
• h
• -
• L
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• ⁢
• 2
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• tan
• ⁡
• (
• α
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• σ
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• L
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• 2
• -
• L
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• 1
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• (
• 1
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• where α denotes an oblique incident angle of a principal ray of the light beam (Ray1) in the sub-scanning direction, which enters the deflecting surface of the deflection unit from a direction oblique to the optical axis of the imaging optical system within the sub-scanning section;
• L1 (mm) denotes an interval in the optical axis direction of the imaging optical system, between a deflection-for-scanning point O and an optical surface on the surface-to-be-scanned side of the imaging optical element (G1), L2 (mm) denotes an interval in the optical axis direction of the imaging optical system, between the deflection-for-scanning point O and a reflection point P of the first reflecting minor (M1);
• h (mm) denotes a length of the imaging optical element (G1) in the sub-scanning direction;
• σ (mm) denotes an interval in the sub-scanning direction between the deflection-for-scanning point O and a profile center C of the imaging optical element (G1);
• and θ (degree) denotes an angle, in the sub-scanning direction, between the principal ray of the light beam (Ray1) reflected by a reflection surface of the first reflecting mirror (M1) and a plane perpendicular to a rotational axis of the deflection unit.