| 摘要 |
An optical system and optical scanning apparatus can form a minute beam spot and big size images. The optical scanning apparatus deflects a beam with a polygon mirror, and focuses the beam on a target surface through a ftheta-lens, a cylindrical lens, and a cylindrical mirror. The scanning stroke on the target surface is longer than 500 mm, and the incident angle in the sub-scan direction of the incident light into the cylindrical mirror is 15 degrees or less. The ratio of the beam size DX in the sub-scan direction of the incident light into the cylindrical mirror to the distance DL between the cylindrical mirror and the target surface satisfies 0.03<DX/DL<0.06.
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