Abstract: In an imaging lens made of three lens sheets, the second and third lenses from the object side are shaped substantially similar to each other, thereby reducing the manufacturing cost while improving resolution. The first lens L1 is a biconcave lens having a surface with a stronger curvature directed onto the object side. Each of the second lens L2 and third lens L3 is a biconvex lens having a surface with a stronger curvature directed onto the imaging surface side, while the second lens L2 and third lens L3 have the same form. As the second lens L2 and third lens L3 have the same form, the cost of manufacturing the imaging lens can be reduced, though being constituted by three sheets of lenses.

Abstract: A five-group zoom lens is formed of, in order from the enlarging side of the zoom lens, a negative first lens group that is movable for focusing and that is stationary during zooming, a positive second lens group, a positive third lens group, a negative fourth lens group, and a positive fifth lens group that is stationary during zooming. The second lens group, the third lens group, and the fourth lens group move relative to one another and relative to the first and fifth lens groups during zooming. The second lens group includes a negative lens component that has a concave lens surface on the reducing side of the zoom lens. The zoom lens satisfies various conditions and may be used in a projection display device or an image pickup device such as a camera.

Abstract: A wide-angle zoom lens is disclosed having five lens groups of negative, positive, positive, negative, and positive refractive power, respectively, in sequential order from the magnification side. The first lens group is fixed during zooming and is formed of first and second subgroups, each of negative refractive power. Each subgroup moves relative to the other subgroup, as well as along the optical axis, during focusing. Further, the second, third and fourth lens groups are each moved along the optical axis such that the spacing between these lens groups varies for zooming and correction of what would otherwise be excessive curvature of field caused by zooming, and the fifth lens group is fixed during zooming. Various conditions are satisfied so as to favorably correct aberrations, provide an image angle of about 70° at the wide-angle end, and provide room on the reducing side for the insertion of a beam-combining prism.

Abstract: In an imaging lens made of three lens sheets, the second and third lenses from the object side are shaped substantially similar to each other, thereby reducing the manufacturing cost while improving resolution. The first lens L1 is a biconcave lens having a surface with a stronger curvature directed onto the object side. Each of the second lens L2 and third lens L3 is a biconvex lens having a surface with a stronger curvature directed onto the imaging surface side, while the second lens L2 and third lens L3 have the same form. As the second lens L2 and third lens L3 have the same form, the cost of manufacturing the imaging lens can be reduced, though being constituted by three sheets of lenses.

Abstract: A zoom lens comprises first to fifth lens groups successively from the enlargement side. The first lens group is fixed upon changing power and has a negative refracting power and a focusing function. The second and third lens groups having a positive refracting power and the fourth lens group having a negative refracting power are moved with a mutual relationship so as to continuously change power and correct the image surface movement caused by the continuous change in power. The fifth lens group has a positive refracting power and is fixed upon changing power. The first to fifth lens groups satisfy predetermined conditional expressions concerning their focal lengths.

Abstract: A wide-angle zoom lens is disclosed having five lens groups of negative, positive, positive, negative, and positive refractive power, respectively, in sequential order from the magnification side. The first lens group is fixed during zooming and is formed of first and second subgroups, each of negative refractive power. Each subgroup moves relative to the other subgroup, as well as along the optical axis, during focusing. Further, the second, third and fourth lens groups are each moved along the optical axis such that the spacing between these lens groups varies for zooming and correction of what would otherwise be excessive curvature of field caused by zooming, and the fifth lens group is fixed during zooming. Various conditions are satisfied so as to favorably correct aberrations, provide an image angle of about 70° at the wide-angle end, and provide room on the reducing side for the insertion of a beam-combining prism.

Abstract: A zoom lens comprises first to fifth lens groups successively from the enlargement side. The first lens group is fixed upon changing power and has a negative refracting power and a focusing function. The second and third lens groups having a positive refracting power and the fourth lens group having a negative refracting power are moved with a mutual relationship so as to continuously change power and correct the image surface movement caused by the continuous change in power. The fifth lens group has a positive refracting power and is fixed upon changing power. The first to fifth lens groups satisfy predetermined conditional expressions concerning their focal lengths.

Abstract: A wide-angle lens of fixed focal length formed of four lens groups of negative, positive, positive and positive refractive power, respectively, in order from the enlarging side is disclosed. The fourth lens group as well as one of the lens groups of among the first lens group, the second lens group and the third lens group are fixed in position. The other two lens groups of among the first lens group, the second lens group and the third lens group are moved during focusing, and specified conditions are satisfied in order to: (1) insure that the wide-angle lens is nearly telecentric on its reducing side, (2) maintain favorable correction of aberrations, (3) maintain a sufficiently large back focus for insertion of necessary components, and (4) enable the wide-angle lens to be compact. Preferably, the movement amount during a given focus adjustment of one of the two moveable lens groups is directly proportional to the movement amount of the other moveable lens group.

Abstract: A wide-angle lens of fixed focal length formed of four lens groups of negative, positive, positive and positive refractive power, respectively, in order from the enlarging side is disclosed. The fourth lens group as well as one of the lens groups of among the first lens group, the second lens group and the third lens group are fixed in position. The other two lens groups of among the first lens group, the second lens group and the third lens group are moved during focusing, and specified conditions are satisfied in order to: (1) insure that the wide-angle lens is nearly telecentric on its reducing side, (2) maintain favorable correction of aberrations, (3) maintain a sufficiently large back focus for insertion of necessary components, and (4) enable the wide-angle lens to be compact. Preferably, the movement amount during a given focus adjustment of one of the two moveable lens groups is directly proportional to the movement amount of the other moveable lens group.

Abstract: A zoom lens for primary use with a projection screen television system is disclosed having five lens groups, in sequential order from the enlarging side, of negative, positive, positive, negative, and positive refractive power. The first lens group and the fifth lens group are fixed, and the axial positions of the second lens group, the third lens group, and the fourth lens group vary when zooming so as to provide a change in magnification and to correct for shifting of the image surface which otherwise would occur with zooming. Specified conditions are satisfied in order to provide a zoom lens that is compact, is well-corrected for aberrations over the entire range of zoom, has a sufficient back focus on the reducing side for insertion of lens components needed for projecting color images, is nearly telecentric on its reducing side, and provides a sufficiently bright image with a wide-angle of view.

Abstract: A zoom lens having a maximum of thirteen lens elements in four lens groups, the four lens groups being of negative, positive, positive, and positive refractive power, in order from the object side. The first lens group G1 and the fourth lens group G4, in order from the object side, are fixed in position relative to the image surface of the zoom lens, and the second lens group G2 and the third lens group G3 move with a mutual relationship for continuous zooming and correction for what would otherwise be a shifting of the image surface of the zoom lens with zooming. Further, certain conditions are preferably satisfied in order to provide a zoom lens that is compact, yet provides a bright image with well-corrected aberrations.

Abstract: An image-forming lens, of the retro-focus type, having only two lens elements is disclosed. By making the object-side of the first lens element, in order from the object side, be a convex surface, and by satisfying two specified conditions, an image forming lens having a wide image angle, low distortion, and with a sufficiently large back focus for insertion of other optical components between the lens and the image plane is achieved, while simultaneously providing a compact and low-cost lens construction. By making at least one surface of each lens element be aspherical, a high-quality image is provided. In the preferred embodiments disclosed, both surfaces of each lens element are made aspherical.

Abstract: An imaging lens is disclosed having two lens groups, both of positive refractive power, a diaphragm positioned between the lens groups, and five or fewer lens elements with no aspherical surfaces. The imaging lens provides a high resolution over a wide image angle. During focusing, only the position of the rear lens group is adjusted relative to the image surface, enabling a low-cost shutter mechanism to be employed as the diaphragm. The front lens group includes, in order from the object side, either a plano-concave or a biconcave lens element and, in addition, a biconvex lens element. The rear lens group includes, in order from the object side, a positive meniscus lens element with its convex surface on the image side, a negative meniscus lens element with its concave surface on the image side, and a biconvex lens element. By having the ratio of the focal length of the positive meniscus lens element of the rear lens group divided by the focal length of the imaging lens be greater than 1.4 and less than 4.

Abstract: An image-forming lens having four lens elements of refractive power, in order from the object side, of: negative, positive, positive, and negative. By making the distance from image-side surface of the first element to the image-side surface of the second lens element to be greater than or equal to 0.3 f and less than or equal to 1.5 f, where f is the focal length of the image-forming lens, an image-forming lens having an F# of approximately 2.8 and a picture angle of about 60 degrees is obtained. A diaphragm may be positioned such that the distance along the optical axis from the diaphragm to the object side of the fourth lens is less than or equal to the focal length of the image-forming lens.

Abstract: An imaging lens is constituted by two lens sheets, in which the lens on the object side is a meniscus lens having a convex surface on the image surface side, and the lens on the image surface side is a meniscus lens having a convex surface on the image surface side, while at least one lens surface is formed as an aspheric surface, thereby realizing smaller size, wider field angle, higher brightness, lower cost, and favorably-corrected various kinds of aberration. A first lens L.sub.1 is a positive meniscus lens having a convex surface directed toward the image surface side, and a second lens L.sub.2 is a positive meniscus lens having a convex surface directed toward the object side. Also, these lenses satisfy the following conditional expressions:0.6.ltoreq..vertline.R.sub.1 /f.vertline..ltoreq.1.35 (1)0.5.ltoreq.R.sub.1 /R.sub.2 .ltoreq.1.

Abstract: An imaging lens with a wide image angle, that is compact and bright, is composed of a first lens group of negative refracting power which has three lens elements which are of positive, negative, and positive refracting power, respectively, and a second lens group of positive refracting power. By providing the first lens element on the object side of the first lens group with an aspherical surface, and by fixing the range of the spacing between the first lens element and the second lens element to satisfy a first condition, as well as fixing the spacing between the second lens element and the third lens element to satisfy a second condition, the distortion of the imaging lens is reduced and its resolution is increased.

Abstract: Successively from an object side, a stop, a biconvex lens, a biconcave lens, a biconvex lens, and a meniscus lens having a convex surface directed onto the image side are disposed, while the image-side surfaces of the second and third lenses are set to have a predetermined range of power, thereby favorably correcting various kinds of aberration, such as distortion in particular, while reducing the size of the whole lens system. Disposed successively from the object side are a stop i, a first lens L.sub.1 made of a biconvex lens, a second lens L.sub.2 made of a biconcave lens, a third lens L.sub.3 made of a biconvex lens, and a fourth lens L.sub.4 made of a meniscus lens having a convex surface directed onto the image side. These lenses satisfy the following conditional expressions :0.4<R.sub.5/ f<2.00.4<.vertline.R.sub.7 .vertline./f<2.2whereinR.sub.5 is a radius of curvature of the surface of the second lens on the image side;R.sub.

Abstract: An image-forming lens made of five lens elements having refractive power, from the object side, of negative, negative, positive, positive, and negative. The distance between the image side of the surfaces of second and third lens elements is made greater than or equal to 3.4 f, and less than or equal to 7.5 f, where f is the focal length of the image-forming lens, so as to minimize spherical aberration, coma, and astigmatism. The image-forming lens thus formed is a retro-focus lens having a half-picture angle of about 80.degree. and an F# of about 1.8.

Abstract: In a configuration constituted by two lens sheets, the ranges of levels of refractive index n and Abbe number .nu. of the image-side lens made of a biconvex lens are specified in order to realize an imaging lens constituted by two lens sheets which can attain a long back focus, a relatively wide angle of view, a high brightness, a small size, and a lower manufacturing cost. The imaging lens comprises, successively disposed from the object side to the image side, a concave lens and a biconvex lens, while at least one surface of the concave lens is an aspheric surface. Also, assuming that the refractive index and Abbe number of the biconvex lens are respectively n and .nu., the following conditional expressions (1) and (2):1.55.ltoreq.n (1)35.ltoreq..nu. (2)are satisfied.