Abstract: An optical scanning device has a rotary polygon mirror and an f-&thgr; lens system which comprises a first lens disposed adjacent to the polygon mirror, a reflection mirror for turning an optical path of the f-&thgr; lens system at an approximately right angle and a second lens disposed in the optical path after the reflection mirror.

Abstract: An image-reading lens is formed of a two lens elements of meniscus shape, one with its convex surface on the most object-side of the image-reading lens and one with its convex surface on the most image-side of the image-reading lens. An intermediate lens element of negative refractive power may be optionally provided. A zone plate diffractive optical surface having different depth zones surrounding a vertex is formed on at least one aspherical surface of the two lens elements of meniscus shape so as to correct simltaneously for both lateral color and curvature of field. Another surface, preferably of the same lens element having the zone plate diffractive/aspherical surface, is made aspherical. Of the two lens elements of meniscus shape, one is made of plastic material and the other is made of non-plastic material. The image reading lens provides a high image quality having a small temperature dependence, despite one lens element thereof being made of plastic material.

Abstract: A compact zoom lens having only four lens groups is provided which changes power by shifting a second lens group from the object side along the optical axis, and stabilizes the image plane position by shifting a fourth lens group from the object side along the optical axis. By satisfying three prescribed conditions, magnification of the image is prevented from decreasing for objects at very near distances, and aberrations are favorably corrected so as to provide for high quality imaging over the entire range of zoom for all object distances. At least one lens element has an aspherical surface.

Abstract: An optical scanner is provided that reduces chromatic aberration (focus error) due to mode hopping of a semiconductor laser light source and that can give high-resolution output applicable to digital copiers and optical printers even when using an imaging optical system having only a few lens elements. At least one surface of the collimating lens includes a zone plate diffractive optical surface which meets specified design conditions to ensure that the focus error due to mode hopping is acceptably small.

Abstract: Successively from an object side, a negative lens having a concave surface directed onto an image surface side, a positive meniscus lens having a convex surface directed onto the image surface side, a positive lens having a convex surface directed onto the image surface side, a negative lens having a concave surface directed onto the image surface side, and a biconvex lens are disposed, thereby yielding a photographic lens for electronic still camera which can favorably correct distortion while attaining a compact size and a wide angle of view. Successively disposed from the object side are a negative first lens L.sub.1 having a concave surface directed onto the image surface side, a second lens L.sub.2 made of a positive meniscus lens having a convex surface directed onto the image surface side, a third lens L.sub.3 made of a biconvex lens whose surface with a stronger curvature is directed onto the image surface side, a negative fourth lens L.sub.

Abstract: The temperature coefficient of refractive index in each lens constituting an imaging lens is controlled such that the amount of change in the imaging position due to change in the imaging lens upon temperature alleviates the positional deviation between the imaging position and the light-receiving surface caused by members other than the imaging lens, thereby preventing the read-out accuracy from deteriorating. The amount of change in the imaging position caused by change in the refractive index of lenses upon change in temperature is adjusted so as to alleviate the positional deviation between the imaging position and light-receiving surface due to the thermal expansion of the member unitedly holding the light source, lenses, and receiving optics.