| 摘要 |
PROBLEM TO BE SOLVED: To excellently correct a field curvature in the horizontal and vertical scanning directions while well keeping a conjugate function and a speed-equalizing function. SOLUTION: A scanning image forming lens in an optical scanner is provided, which optically scans a plane to be scanned 8 with an equal velocity by deflecting an image-formed luminous flux in a long line image in the direction corresponding to the horizontal scanning with an equal angular velocity by a light deflector 5 having deflecting reflection planes 5A in the neighborhood of the image-formed position of the above-mentioned line image, and is composed of two lenses 6, 7; the lens 6 on the side of the light deflector 5 is a positive meniscus lens with its concave surface faced to the side of the light deflector; both surfaces are coaxial and aspherical; and at least, one of the surfaces of the lens 7 on the side of the plane to be scanned 8 has a non-circular arc shape and also a radius of curvature in the above-mentioned vertical scanning cross-section is varied in the direction corresponding to the horizontal scanning so that centers of curvatures lined with the centers of curvatures in the vertical scanning cross-section of the lens surface in the direction corresponding to the horizontal scanning forms a curve different from the above-mentioned non-circular arc shape in the horizontal scanning cross-section. |
