Abstract: A lens system comprising a radial type graded refractive index lens element and a diffraction type lens element so that the refractive power of the radial type graded refractive index lens element is imparted to the diffraction type lens element, thereby facilitating manufacturing of the graded refractive index lens element and favorably correcting aberrations including chromatic aberration.

Abstract: An imaging optical system using index distribution type optical elements comprises an imaging optical system for forming the image of an object on a light receiving surface, is formed by a plurality of optical elements of erect one-to-one magnification having a radial index distribution arranged in a row and satisfies the following relations: ##EQU1## D is the effective diameter of each optical element, Xo is the field radius of each optical element, and P is the arrangement interval of the optical elements.

Abstract: A zoom lens system comprising at least a first lens unit having a positive refractive power as a whole, a second lens unit having a negative refractive power as a whole and a third lens unit having a positive refractive power as a whole, and adapted to perform variation of focal length by varying at least two airspaces reserved between said lens units. This zoom lens system consists of a small number of lens elements, has a short total length and a compact external design, and is light in weight.

Abstract: A compact vari-focal lens system comprising, in the order from the object side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power and a third lens unit having a negative refractive power, and uses at least one radial type graded refractive index lens element arranged at the image side location in the second lens unit. The varifocal lens system has a high vari-focal ratio and aberrations corrected favorably over the entire vari-focal range from the wide position to the tele position, and consists of a very small number of lens elements.

Abstract: A vari-focal lens system including, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, an aperture stop, a third lens unit having a positive refractive power and a fourth lens unit having a negative refractive power; and using at least one radial GRIN lens element on each side of the aperture stop. This vari-focal lens system has only a very small number of lens elements and had favorably corrected aberrations.

Abstract: An imaging lens system comprising, in the order from the object side, a first lens component having a convex surface on the object side and a positive refractive power, a second lens component having a concave surface on the image side and a negative refractive power, and a third lens component. Through the imaging lens system is of a triplet or Tessar type, the lens system is designed so as to have a high aperture ratio and favorably corrected coma by arranging a radial GRIN lens element having a concave surface on the image side and a positive refractive power at the most image side location in the third lens component.

Abstract: A gradient index optical element includes a first metal which is at least one kind of metal selected from the metals of Group A each having the content of 10-40 mol % in terms of oxide and a second metal which is at least one kind of metal selected from the metals of Group B each having the content of 2-15 mol % in terms of oxide, in which the first and second metals are distributed so that the concentration of one of said first and second metals increases from the center of the optical element toward the periphery and that of the other decreases. Hence, the gradient index optical element has an important advantage in practical use that the correction for chromatic aberration is excellent, that is, the Abbe's number increases as the refractive index becomes great.

Abstract: An objective for an optical data storage read/write head focuses a laser beam at a spot on an optical recording surface protected by a transparent cover of an optical disc. The imaging is provided by a gradient index singlet lens having bending and an index gradient which is selected depending on the thickness of the lens and the thickness of the cover over the recording surface so as to provide aberration correction over a paraxial image height of the spot which tolerates tracking errors (displacements with respect to the track) on the recording surface. The objective desirably obtains its power exclusively from the curvature of its surfaces, with the index gradient providing for aberration correction. The gradient is preferably axial, decreasing from the vertex at the front surface (the surface on which the laser beam is incident) over a sag distance along the optical axis towards the back surface, which is opposite to the cover of the optical data storage device.

Abstract: The present invention relates to an optical element and catadioptric optical systems using the optical element. The optical element has a spherical surface with a reflective layer formed on at least a portion of the surface, and is formed of a radiant energy transmitting material having a radial gradient index of refraction. The catadioptric optical systems include at least two optical elements at least one of which is refractive, and at least one of which has a gradient index therein. One optical system includes first and second optical elements disposed sequentially along a longitudinal axis of the system. The second optical element is the optical element with the gradient index. The first optical element is formed of a homogeneous light transmitting material and includes a spherical surface, and a reflective layer formed on a central portion of one of the spherical surface.

Abstract: A vari-focal lens system comprising, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power and an aperture stop arranged on the image side of said third lens unit, using at least one radial GRIN lens, axial GRIN lens or aspherical surface, and having a high vari-focal ratio and a wide field angle at the wide position.

Abstract: Distortion of the image displayed by a cathode ray tube display (10,10') can be compensated by placing a flat-plate optical device, fabricated from two plates (14,14') of optical material joined at their edges an an angle, in the field of view of the display. Each of the plates (14,14') is advantageously constructed so as to have a gradient index of refraction such that the index of the plate changes across its length from its free edge to the vertex (16) formed with the other plate. By fabricating each of the plates (14 and 14') such that the index of refraction of each decreases or increases from the free edge of each plate to the vertex formed with the other plate, the device formed by the plates will compensate for either barrel or pincushion distortion, respectively.

Abstract: A zoom lens system comprising a plural number of lens units, so adapted as to perform variation of focal length by varying airspace reserved between each pair of the lens units and comprising, in a negative lens unit arranged in a vari-focal lens group, at least one radial GRIN lens component having a concave shape and refractive index lowered as the lens portions are farther from the optical axis toward the outer circumference in the direction perpendicular to the optical axis.

Abstract: A lens system comprising, at locations in the vicinity of each other, radial type graded refractive index lens elements made of a medium having a positive refractive power and other radial type graded refractive index lens elements made of a medium having a negative refractive power. This lens system has aberrations corrected favorably with the radial type graded refractive index lens elements which are made of materials easily preparable.

Abstract: A compact vari-focal lens system having a high vari-focal ratio, comprising a plurality of lens units including at least one lens unit having a positive refractive power and at least one lens unit having a negative refractive power, and adapted so as to change focal length thereof by moving one of said lens units along the optical axis, the lens unit arranged on the extremely object in said lens system having a positive refractive power and at least one radial GRIN lens being used in a negative lens unit.

Abstract: A graded-index lens for focusing an erect unmagnified image out of the lens has a refractive index varying radially in a cross-sectional plane normal to the optical axis thereof. The graded-index lens comprises a cylindrical medium whose refractive index at a radial distance r from an optical axis within a cross-sectional plane normal to the optical axis, is expressed by:n.sup.2 (r)=n.sub.0.sup.2 [1-(gr).sup.2 +h.sub.4 (gr).sup.4 ]where n.sub.0 is the refractive index on the optical axis, g is a parameter indicating the gradient of the varying refractive index, and h.sub.4 is a fourth-order refractive index distribution coefficient, the fourth-order refractive index distribution coefficient h.sub.4 being in the range of:0.6<h.sub.4 <1.0.

Abstract: A vari-focal lens system comprising a first lens unit having positive refractive power and arranged on the extremely object side, a second lens unit having negative refractive power and arranged on the image side of the first lens unit, and a rear lens unit having negative refractive power, at least one lens component arranged in the rear lens unit being designed as a negative graded refractive index lens.

Abstract: An objective lens system for microscopes comprising a plurality of lens units including a first lens unit arranged at the foremost location and having a positive refractive power, and using a GRIN lens or GRIN lenses designed taking into consideration the characteristic of the glass materials currently available. The objective lens system for microscopes consists of a small number of lens elements and has favorably corrected aberrations.

Abstract: A zoom lens comprising a plurality of lens units in which at least one of the air separations between the units is varied to effect zooming, whereby at least one of the plurality of lens units is included with at least one refractive index distribution type lens element on a common optical axis of the other elements.

Abstract: A high performance, compact, light-weight zoom lens system manufacturable at a low cost consisting of a plural number of lens units and so adapted as to perform zooming by varying airspace(s) reserved between the lens units, said zoom lens system comprising, in the order from the object side, a first lens unit having negative refractive power, an aperture stop arranged on the image side of said first lens unit, and at least one radial GRIN lens component arranged on the image side of said aperture stop, having a concave shape and having positive power.