Abstract: An optical system for focusing an original image on an image sensor has an optical element disposed at the image-sensor-side end thereof. The optical element has a positive optical power as a whole, and at least one surface of the optical element has a positive optical power of diffraction.

Abstract: A zoom lens system consists of, in order from the enlargement side to the reduction side, a first lens unit having a negative optical power and a second lens unit having a positive optical power. In the zoom lens system, either the first or the second lens unit has at least one surface having an optical power of diffraction.

Abstract: A zoom lens system has, from the enlargement side, a first lens unit having a negative optical power and having a lens element including a diffractive optical surface, a second lens unit having a positive optical power, and a third lens unit. Zooming is performed by varying the distances among the first through third lens units. The following conditions are fulfilled: |&phgr;Dn/&phgr;1|<0.06 −0.8<&phgr;n/&phgr;W<−0.3 where &phgr;Dn represents the diffractive optical power of the first lens unit, &phgr;1 represents the refractive optical power of the lens element including the diffractive optical surface, &phgr;n represents the composite optical power of the diffractive and refractive optical powers of the first lens unit, and &phgr;W represents the composite optical power of the diffractive and refractive optical powers of the entire lens system in the shortest-focal-length condition.

Abstract: A radial gradient index lens system has a refractive index distribution. The refractive index decreases from an optical axis along a height. The lens system has two meniscus lens elements whose convex surfaces have a larger radius of curvature than concave surfaces. The meniscus lens elements are arranged symmetrically with respect to an aperture stop so that the convex surfaces thereof face an object side and an image side, respectively. The gradient index lens system is for use in a copying apparatus or as a reading optical system.

Abstract: A finite conjugate distance zoom lens system includes sequentially from the enlarging side a first lens group having a negative refracting power and a second lens group having a positive refracting power. The second lens group consists of sequentially from the enlarging side two or three positive lens elements, first and second cemented lenses, a negative lens element, and a positive lens element. Both of the first and second lenses consist of cemented biconvex lens element and negative lens element. During a zooming operation from the maximum focal length edge to the minimum focal length edge, the first lens group shifts from the enlarging side to the reducing side on the maximum focal length side and shifts from the reducing side to the enlarging side on the minimum focal length side. On the other hand, the second lens group monotonously shifts from the enlarging side to the reducing side during the zooming operation.

Abstract: A three group, three component lens system comprising, in order from one side a first, positive meniscus lens defining a convex surface directed to an object, a second, biconcave lens, and a third, biconvex lens. At least one of the three lenses is formed of plastic. It is recommended to satisfy the following conditional expression:0.1 f<f1+f2<0.2fwhere f is a focal length of the entire lens system, f1 is a focal length of said first lens, and f2 is a focal length of said second lens.

Abstract: A symmetrical lens system comprising, as arranged from the object side toward the image side, a first lens in the form of a positive meniscus lens having its convex surface directed toward the object side, a second lens in the form of a negative meniscus lens having its convex surface directed toward the object side, a diaphragm, a third lens in the form of a negative meniscus lens symmetrical with the second lens with respect to the diaphragm, and a fourth lens in the form of a positive meniscus lens symmetrical with the first lens with respect to the diaphragm. At least, the concave surface of the first lens and the fourth lens is aspherical.

Abstract: A light-transmission viewing screen for displaying an optical image from a beam of light projected thereon along a predetermined path of light provided rearwardly of the screen, the viewing screen having a virtual center axis extending toward a viewer's viewing position, the light-transmission viewing screen comprising a transparent or translucent transmission screen plate through which to transmit the beam of light, and a transmission grating located on at least a portion of one of the surfaces of the transmission screen plate for diffracting the beam of light toward a location substantially aligned with the virtual center axis of the viewing screen when the beam of light is transmitted through the transmission grating.

Abstract: A focusing device for use in micro film readers or the like for projecting micro images to give in-focus conditon exactly and readily. The present device includes a memory for storing a distance data representing the distance between an original and a projective lens at in-focus position thereof, and a sensor for measuring the distance between an original and the projective lens wherein the projective lens is moved to the in-focus position by a focusing motor in response to the distance data stored in the memory and a signal representing the measured distance generated from the sensor.