Abstract: A zoom lens with a large zoom ratio suitable for surveillance cameras includes, and may only include, four lens groups, in order from the object side, a first lens group of positive refractive power, a second lens group of negative refractive power, a third lens group of positive refractive power, and a fourth lens group of negative refractive power. The second and third lens groups move during zooming. Each of the first, second, and third lens groups is formed of three lens elements that comprise two lens components of particular constructions. Certain conditions are satisfied by the ratio of the focal lengths of the first lens group and the zoom lens, the ratio of focal lengths of the second and third lens groups, and the arithmetic mean of the Abbe numbers and indexes of refraction of lens elements having positive refractive power in the first lens group.

Abstract: A zoom lens with a large zoom ratio suitable for surveillance cameras includes, and may only include, four lens groups, in order from the object side, a first lens group of positive refractive power, a second lens group of negative refractive power, a third lens group of positive refractive power, and a fourth lens group of negative refractive power. The second and third lens groups move during zooming. Each of the first, second, and third lens groups is formed of three lens elements that comprise two lens components of particular constructions. Certain conditions are satisfied by the ratio of the focal lengths of the first lens group and the zoom lens, the ratio of focal lengths of the second and third lens groups, and the arithmetic mean of the Abbe numbers and indexes of refraction of lens elements having positive refractive power in the first lens group.

Abstract: A rear focus zoom lens is disclosed that includes, in order from the object side: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power and including a stop; a fourth lens group having negative refractive power; and a fifth lens group having positive refractive power. The second lens group and the third lens group are moved along the optical axis for zooming, the fourth lens group is moved along the optical axis for focusing, and the fourth lens group comprises a doublet consisting of a negative lens element and a positive lens element. The fifth lens group may have a specified configuration which includes an aspherical surface and that satisfies a specified condition which insures that aberrations are satisfactorily corrected over the entire range of zoom.

Abstract: A compact two-group zoom lens that corrects aberrations in the visible and the near infrared regions and that provides a comparatively high zoom ratio includes, in order from the object side, a first lens group of negative refractive power and a second lens group of positive refractive power. The first lens group includes, in order from the object side, first and second negative meniscus lens elements having convex surfaces on the object side, a biconcave lens element, and a positive lens element. The second lens group includes, in order from the object side, a positive lens component which may be a lens element, a negative/positive doublet component, and a negative lens component which may be a lens element. Aspheric lens surfaces are disclosed. Certain conditions are satisfied to control aberrations in both the visible and the near infrared and to ensure a sufficient back focus distance.

Abstract: A rear focus zoom lens is disclosed that includes, in order from the object side: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power and including a stop; a fourth lens group having negative refractive power; and a fifth lens group having positive refractive power. The second lens group and the third lens group are moved along the optical axis for zooming, the fourth lens group is moved along the optical axis for focusing, and the fourth lens group comprises a doublet consisting of a negative lens element and a positive lens element. The fifth lens group may have a specified configuration which includes an aspherical surface and that satisfies a specified condition which insures that aberrations are satisfactorily corrected over the entire range of zoom.

Abstract: A wide-angle zoom lens is disclosed having only two lens groups, of negative and positive refractive power in order from the object side, respectively, and which provides an image angle at the wide-angle end of at least 100°. Zooming is performed by moving the first lens group and the second lens group along the optical axis. The first lens group is formed of, in sequential order from the object side, a negative meniscus lens element with its convex surface on the object side, two negative lens elements, and a positive lens element. The second lens group is formed of, in sequential order from the object side, two positive lens elements, a biconcave lens element, and two positive lens elements. Various conditions are preferably satisfied so as to minimize aberrations and make the zoom lens compact and easy to manufacture.

Abstract: A compact two-group zoom lens that corrects aberrations in the visible and the near infrared regions and that provides a comparatively high zoom ratio includes, in order from the object side, a first lens group of negative refractive power and a second lens group of positive refractive power. The first lens group includes, in order from the object side, first and second negative meniscus lens elements having convex surfaces on the object side, a biconcave lens element, and a positive lens element. The second lens group includes, in order from the object side, a positive lens component which may be a lens element, a negative/positive doublet component, and a negative lens component which may be a lens element. Aspheric lens surfaces are disclosed. Certain conditions are satisfied to control aberrations in both the visible and the near infrared and to ensure a sufficient back focus distance.

Abstract: A retrofocus wide-angle lens includes a first lens group of negative refractive power, a diaphragm, and a second lens group of positive refractive power. The first lens group includes an object-side lens group, a middle lens group, and an image-side lens group. The object-side lens group includes a plurality of negative lens components and a positive meniscus lens component with its convex surface on the image side. The middle lens group satisfies a particular focal length condition and includes a negative lens component at the object side. The image-side lens group includes a negative lens element and a positive lens element. The first and second lens groups include lens elements of opposite refractive power that are made of anomalous dispersion glass so as to provide chromatic aberration correction and to compensate for variations in refractive index with temperature change that would otherwise cause the focal length to vary with temperature.

Abstract: A wide-angle zoom lens is disclosed having only two lens groups, of negative and positive refractive power in order from the object side, respectively, and which provides an image angle at the wide-angle end of at least 100°. Zooming is performed by moving the first lens group and the second lens group along the optical axis. The first lens group is formed of, in sequential order from the object side, a negative meniscus lens element with its convex surface on the object side, two negative lens elements, and a positive lens element. The second lens group is formed of, in sequential order from the object side, two positive lens elements, a biconcave lens element, and two positive lens elements. Various conditions are preferably satisfied so as to minimize aberrations and make the zoom lens compact and easy to manufacture.

Abstract: A retro-focus-type camera lens is disclosed that is formed of, in order from the object side: a front lens group having negative refractive power, a diaphragm, and a rear lens group having positive refractive power. The front lens group is formed of, in order from the object side, a positive lens element and two negative lens elements, and the rear lens group is formed of, in order from the object side, a positive lens element, two sets of lens elements that are cemented together to form two joined lenses, and a positive lens element. Various conditions are preferably satisfied in order to provide a lens having an image angle of about 38°, an F number of about 1.4, and which suppresses the occurrence of color shading while providing a sufficient back focus to insert a color separation optical system between the retro-focus-type camera lens and the image plane.

Abstract: A retrofocus wide-angle lens includes a first lens group of negative refractive power, a diaphragm, and a second lens group of positive refractive power. The first lens group includes an object-side lens group, a middle lens group, and an image-side lens group. The object-side lens group includes a plurality of negative lens components and a positive meniscus lens component with its convex surface on the image side. The middle lens group satisfies a particular focal length condition and includes a negative lens component at the object side. The image-side lens group includes a negative lens element and a positive lens element. The first and second lens groups include lens elements of opposite refractive power that are made of anomalous dispersion glass so as to provide chromatic aberration correction and to compensate for variations in refractive index with temperature change that would otherwise cause the focal length to vary with temperature.

Abstract: A wide-angle zoom lens is disclosed having only two lens groups, of negative and positive refractive power in order from the object side, respectively, and which provides an image angle at the wide-angle end of at least 100°. Zooming is performed by moving the first lens group and the second lens group along the optical axis. The first lens group is formed of, in sequential order from the object side, a negative meniscus lens element with its convex surface on the object side, two negative lens elements, and a positive lens element. The second lens group is formed of, in sequential order from the object side, two positive lens elements, a biconcave lens element, and two positive lens elements. Various conditions are preferably satisfied so as to minimize aberrations and make the zoom lens compact and easy to manufacture.

Abstract: A retro-focus-type camera lens is disclosed that is formed of, in order from the object side: a front lens group having negative refractive power, a diaphragm, and a rear lens group having positive refractive power. The front lens group is formed of, in order from the object side, a positive lens element and two negative lens elements, and the rear lens group is formed of, in order from the object side, a positive lens element, two sets of lens elements that are cemented together to form two joined lenses, and a positive lens element. Various conditions are preferably satisfied in order to provide a lens having an image angle of about 38°, an F number of about 1.4, and which suppresses the occurrence of color shading while providing a sufficient back focus to insert a color separation optical system between the retro-focus-type camera lens and the image plane.

Abstract: A Gaussian lens having no more than six lens elements of refractive power is formed of, in order from the object side: a first lens element which is biconvex, a second lens element which is a positive meniscus lens with its convex surface on the object side, a third lens element which is biconcave, a stop, a joined lens formed of a fourth lens element which is biconcave that is joined to a fifth lens element which is biconvex; and a sixth lens element having positive refractive power. Specified conditions are satisfied in order to provide a compact lens having an f-number FNO of 1.44 or less, an image angle 2&ohgr; of 23.8 degrees or more, and wherein the various aberrations are favorably corrected. The Gaussian lens of the invention is intended for mounting in monitor cameras.

Abstract: A wide-angle zoom lens is provided having only three lens groups of, in order from the object side, negative, positive, and positive refractive power, respectively. The fist lens group is formed of only two lens elements, each of negative refractive power. The wide-angle zoom lens is compact and achieves high optical performance over the entire range of zoom by satisfying predetermined conditions. When power is varied during zooming, the first lens group and the second lens group are moved along the optical axis, and the third lens group remains in a fixed position. During focusing, the first lens group is moved along the optical axis.

Abstract: A rear-focus-type zoom lens having, in order from the object side, four lens groups of positive, negative, positive, and positive power, wherein the first lens group G1 and the third lens group G3 are fixed and the second lens group G2 and the fourth lens group G4 are moved during zooming. Focusing is accomplished by moving the fourth lens group G4. The first lens group G1 is formed of a negative lens element L1 and positive lens element L2 that are joined together, and a positive lens element L3. The second lens group G2 is formed of, in order from the object side, a negative lens element L4 and a lens formed of a negative lens element L5 and a positive lens element L6 that are joined. The third lens group G3 is formed of a single lens element L7, and the fourth lens group G4 is formed, in order from the object side, of positive, negative, positive, and positive lens elements L8-L11, respectively. Further, specified conditions are satisfied.

Abstract: A Gaussian lens having no more than six lens elements of refractive power is formed of, in order from the object side: a first lens element which is biconvex, a second lens element which is a positive meniscus lens with its convex surface on the object side, a third lens element which is biconcave, a stop, a joined lens formed of a fourth lens element which is biconcave that is joined to a fifth lens element which is biconvex; and a sixth lens element having positive refractive power. Specified conditions are satisfied in order to provide a compact lens having an f-number FNO of 1.44 or less, an image angle 2&ohgr; of 23.8 degrees or more, and wherein the various aberrations are favorably corrected. The Gaussian lens of the invention is intended for mounting in monitor cameras.

Abstract: A wide-angle zoom lens is provided having only three lens groups of, in order from the object side, negative, positive, and positive refractive power, respectively. The fist lens group is formed of only two lens elements, each of negative refractive power. The wide-angle zoom lens is compact and achieves high optical performance over the entire range of zoom by satisfying predetermined conditions. When power is varied during zooming, the first lens group and the second lens group are moved along the optical axis, and the third lens group remains in a fixed position. During focusing, the first lens group is moved along the optical axis.

Abstract: A modified Gaussian lens comprises, successively from the object side, meniscus first and second lenses L1 and L2 each having a positive refracting power with a convex surface directed onto the object side, a meniscus third lens L3 having a negative refracting power with a concave surface directed onto the image side, a meniscus fourth lens L4 having a negative refracting power with a concave surface directed onto the object side, and a fifth lens L5 made of a biconvex lens; and satisfies the following conditional expressions (1) to (6): (1) 0.37<f1,2/f<0.57, (2) 0.62<&Sgr;d/f<1.03, (3) 0.13<L/f<0.26, (4) 22.0<&ngr;2−&ngr;3<36.0, (5) 6.0<(1/R6+1/|R7|)×f<11.2, (6) −1.72<R10/R1121 0. Thus, while in a compact, five-group, five-element configuration, high performances and conditions suitable for a relatively telephoto lens mounted to a monitor camera or the like, i.e., an F number of about 1.

Abstract: A retro-focus type wide-angle lens attains a wide angle of view of 100 degrees in terms of taking angle of view, a far exit pupil position so as to suppress the occurrence of color shading, and a long back focus which is five times the focal length, thus being sufficient for disposing a three-color-separating optical system. The wide-angle lens comprises, successively from the object side, a first lens group G1, having a negative refracting power, constituted by a negative first-a lens group G1a and a positive first-b lens group G1b, and a second lens group G2 having a positive refracting power; and satisfies the following conditional expressions (1) and (2): 5.0<Bf/f  (1) −0.05<tan &thgr;<0.05  (2) where f is the focal length of the whole system; Bf is the back focus of the whole system; and &thgr;is an angle formed between a principal ray directed to a screen corner portion and an optical axis.