Ricoh Company, Ltd.

Kabushiki Kaisha Ricoh

Hiroichi Shinohara

A variable focus lens for use in reproducing images includes first, second, third, and fourth lens groups arranged successively from an object to an image, and a diaphragm disposed between the second and third lens groups. The first lens group comprises a concave meniscus lens with its concave surface facing the object. The second lens group comprises a double convex lens with the larger absolute value of the radius of curvature of its surface facing the image, a double concave lens with the larger absolute value of the radius of curvature of its surface facing the object, and a double convex lens, the lenses being arranged successively in the order named from the object. The third lens group is of the same construction as the second lens group except that the lenses of the third lens group are arranged and faced in the opposite direction to the second lens group, the second and third lens groups being positioned symmetrically with respect to the diaphragm. The fourth lens group comprises an lens identical to the lens of the first lens group and faced in the opposite direction to the first lens group, the first and fourth lens groups being positioned symmetrically with respect to the diaphragm. The first and fourth lens groups and the diaphragm are fixed, whereas the second and third lens groups are movable, the first through fourth lens groups being positioned symmetrically with respect to the diaphragm at an equal-size magnification ratio.

Variable focus lens for image reproduction

A high resolving power Gaussian lens used for a facsimile or the like which uses high-density solid image forming elements. To achieve this object, it is necessary to maintain a high resolving power to cover the marginal portion of the image plane. In the Gaussian lens comprising four groups of lenses and being symmetrical to a diaphragm, each lens group comprises a cemented lens composed of a positive meniscus lens with a concave surface directed toward the diaphragm and a negative meniscus lens. The positive lens has a refractive index in excess of 1.74 to flatten an image surface. The second lens group and the third lens group are reduced in thickness to make it possible to have a wider angle.

Gaussian lens

A stop is disposed forwardly of the lens system which comprises three individual lenses. A first lens located nearest the stop represents a positive meniscus lens, followed by a second and a third individual lens, both of which represent negative meniscus lenses. Each of the first to the third lens has its concave surface directed toward the stop. A small air gap exists between the second and the first lens. Representing the focal length of the first lens by f.sub.1, the composite focal length of the first and the second lens by f.sub.1,2, the composite focal length of the first to the third lens by f, the radius of curvature of a second refractive surface in the lens system by r.sub.3, the radius of curvature of a third refractive surface by r.sub.4, the refractive index of the first lens by n.sub.1, and the Abbe number of the first and the second lens by .nu..sub.1, .nu..sub.2, respectively, these parameters satisfy the following inequalities.

Wide angle copying lens with high aperture efficiency

An improved tessor type lens system for facsimile having a large aperture ratio and a high contrast are provided. The lens system comprises for components between object and image as follows; a first positive meniscus lens element, a second biconcave lens element, a third meniscus shaped doublet. The entire lens system is capable of providing an aperture ratio greater than 90% and a half angle of image of approximately 18.degree. with an f number of 4.5.

Tessor type lens systems for facsimile

A reproduction lens assembly including two groups of three elements for providing a large aperture efficiency and a compact size formed by arranging a lens system symmetrically with respect to a stop wherein the each group of three elements further comprise a first convex Meniscus lens having a concave surface thereof directed toward the stop, the stop being positioned on the front side of the first Meniscus lens, a second concave Meniscus lens having a concave surface thereof directed toward the stop and a third convex Meniscus lens having a concave surface thereof directed toward the stop with a small air gap the third and second Meniscus lens.

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Yokohama, Japan

Hiroichi Shinohara