Abstract: A wide-angle lens system includes a negative front lens group and a positive rear lens group, in this order from the object. The negative front lens group includes a negative first sub-lens group and a positive second sub-lens group, in this order from the object. The positive rear lens group includes cemented lens elements having a positive R1 lens element and a negative R2 lens element, a positive R3 lens element having a convex surface facing toward the image, and a positive R4 lens element, in this order from the object. The wide-angle lens system satisfies the following conditions: ?0.8<f1a/f1b<?0.1 ??(1) 0.6<f/fR<1.1 ??(2) wherein f1a designates the focal length of the negative first sub-lens group; f1b designates the focal length of the positive second sub-lens group; f designates the focal length of the entire wide-angle lens system; and fR designates the focal length of the positive rear lens group.

Abstract: A fisheye lens system includes a negative first lens group and a positive second lens group, which are defined with respect to a maximum air-distance between lens elements constituting the fisheye lens system. The negative first lens group includes a first negative meniscus lens element having the convex surface facing toward the object, a second negative meniscus lens element having the convex surface facing toward the object, and a negative third lens element.

Abstract: A wide-angle lens system includes a negative first lens group, and a positive second lens group. The first lens group includes a positive lens element, and a negative lens element. The wide-angle lens system satisfies the following conditions: 0<(&phgr;1-2+&phgr;2-1)/&phgr;<0.3 . . . (1); 0.5<HF/HL<0.9 . . .

Abstract: A retrofocus wide-angle lens is formed of only three lens groups, in order from the object side, a first lens group of negative refractive power, a second lens group that includes a stop, and a third lens group of positive refractive power. The first lens group is at the object end of the retrofocus wide-angle lens and includes, in order from the object side, a plurality of negative lens components and a plurality of positive lens components. The first lens group includes three lens groups with particular lens features, the first of which, from the object side, also includes two lens groups with particular features. Various combinations of lens elements satisfy two conditions for ratios of absolute values of focal lengths for the various combinations of lens elements that assist in achieving excellent imaging.

Abstract: In a wide-angle lens system having a long back focal length, the various types of aberration, particularly distortion, are kept small. The wide-angle lens system 100 is disposed in front of a ⅓″ CCD camera 40 and the focal length (f) for all lens groups is 3.0 mm, the F-number is 3.0 and the half-field angle is 46°.

Abstract: The improved inner-focus, wide-angle lens system of retrofocus configuration comprises, in order from the object side, a negative first lens group 10, a positive second lens group 20, and a positive third lens group 30 having a diaphragm; the second lens group 20 moves along the optical axis during focusing and the lens system satisfies the following conditions (1) and (2): 0.5<|f1/f|<1.2  (1) 0.7<f2/f<1.8  (2) where f is the focal length of the overall system at focusing at infinity, f1 is the focal length of the first lens group, and f2 is the focal length of the second lens group. The lens system has a half viewing angle of about 44° and an F number of about 3.5.

Abstract: An image-capturing lens is formed of front and rear lens groups having negative and positive refractive power, respectively, in order from the object side. The rear lens group is formed of, in relative sequential order from the most object side of the rear lens group, a biconvex lens element that is cemented to a biconcave lens element, a biconvex lens element, and a biconvex lens element. A specified condition is satisfied so as to make the cemented lens of the rear lens group insensitive to de-centering errors which may occur either in making the cemented lens or in assembling the image-capturing lens.

Abstract: A wide-angle lens system includes a negative first lens group, and a positive second lens group, in this order from the object. The second lens group includes a positive 2F sub-lens group and a positive 2R sub-lens, in this order from the object. Upon focusing from infinity to a closer object distance, an Fa lens group constituted by the first lens group and the positive 2F sub-lens group which are arranged to move integrally, and an Fb lens group constituted by the positive 2R sub-lens group are independently moved from the image side toward the object side so that the distance between the Fa lens group and the Fb lens group are made shorter.

Abstract: A retro focus type wide-angle lens comprises a front group having a negative refracting power and a rear group having a positive refracting power. The front group comprises a first lens made of a negative meniscus lens, a second lens made of a biconvex lens, a third lens made of a negative meniscus lens, and a fourth lens made of a positive meniscus lens. The rear group comprises a cemented lens in which a fifth lens made of a negative lens and a sixth lens made of a positive lens are cemented together, and a seventh lens made of a positive lens. This wide-angle lens further satisfies predetermined conditional expressions.

Abstract: A projection optical system has, from the enlargement side to the reduction side, a first, a second, and a third lens unit, and an aperture diaphragm. The negatively-powered first lens unit includes only a negative lens element and has at least one aspherical surface. The positively-powered second lens unit includes at least one positive lens element. The positively-powered third lens unit includes a lens element. The aperture diaphragm is disposed at the front focal point of the third lens unit. The lens element of the third lens unit is made of a material of which anomalous partial dispersibility and Abbe number are defined.

Abstract: A wide-angle lens system includes a negative first lens group and a positive second lens group with a diaphragm, in this order from an object. Upon focusing, the positive second lens group is arranged to be moved along the optical axis.

Abstract: In an imaging lens unit configured of two lenses, the deterioration of the optical performance due to the eccentricity is suppressed for an improved assembling property, while at the same time correcting the various aberrations in satisfactory manner. A meniscus first lens (L1) having a weak refracting power, and a meniscus second lens (L2) having positive refracting power with the convex surface thereof directed toward the image surface are arranged sequentially from the object side toward the image surface (IMG). The conditions f2/f>0.9 and nd2>1.55 are met, where f is the focal length of the whole lens system, f2 the focal length of the second lens, and nd2 the refractive index on the d line of the second lens.

Abstract: A retro focus lens having three lens groups arranged, in order from the longer conjugate length side of the lens, as follows: a negative first lens group G.sub.1, a positive second lens group G.sub.2, and a positive third lens group G.sub.3. The first group G.sub.1 includes, in order from the longer conjugate length side of the lens, a first lens element L.sub.1 of small positive refractive power and made of plastic with an aspherical surface, a second lens element L.sub.2 of negative refractive power that is made of glass and has a concave surface facing the shorter conjugate length side of the lens, and a third lens element L.sub.3 of negative refractive power with a concave surface facing the shorter conjugate length side of the lens, there being no additional lens elements between the first lens element L.sub.1 and the third lens element L.sub.3.

Abstract: In a large-aperture lens for low-illuminance imaging, a Gauss type lens configuration is employed, and a negative lens having a predetermined refracting power is inserted in front of the front-side cemented lens, whereby back focus is secured while compactness is attained, without using an aspherical lens. Successively disposed from the object side are a biconvex lens L.sub.1, a positive meniscus lens L.sub.2 having a convex surface directed onto the object side, a negative lens L.sub.3 having a concave surface with a stronger curvature directed onto the image side, a positive meniscus lens L.sub.4 (cemented with lens L.sub.5) having a convex surface directed onto the object side, a negative meniscus lens L.sub.5 having a concave surface directed onto the image side, a biconcave lens L.sub.6 (cemented with lens L.sub.7) having a surface with a stronger curvature directed onto the object side, biconvex lenses L.sub.7 and L.sub.

Abstract: In an image forming optical lens system comprising in order from the object end a first lens group of at least two components, a second lens group which has a positive focal length and comprises in order from the object end a first component of positive power, a second component of negative power and a third component of positive power, and a third lens group of at least one component, the components of the lens system are made of at least two different kinds of materials having differences in dispersion of 0.0055 at the greatest from one another and the first to third components of the second lens group are made of materials different in dispersion from one another.

Abstract: A wide angle lens is made of three groups so as to satisfy a predetermined conditional expression concerning abbe number, thereby making it telecentric and yielding no eclipse in its peripheral luminous flux. Also, an apparatus accommodating it is made compact as a whole. This wide angle lens comprises, arranged in the following order from the screen side toward the liquid crystal side, a first lens group composed of a concave lens (L1), whose concave surface having a large radius of curvature is directed toward a smaller conjugate side (liquid crystal panel), and a convex lens (L2); a second lens group composed of one concave lens (L3) and two convex lenses (L4) and (L5); and a third lens group composed of a Fresnel lens (L6) which is disposed near a liquid crystal panel (L7; 4). The abbe number .nu. 1 of the lens L1 which is the concave lens in the first lens group is 57.8, whereas the abbe number .nu. 2 of the lens (L3) which is the concave lens in the second lens group is 25.

Abstract: A fast photographic lens system comprises a first lens having a positive refractive power, a convex-shaped outer face and a flat inner face; a second lens having a positive refractive power, a convex-shaped outer face and a concave-shaped inner face; a third lens having a negative refractive power, a slightly convex-shaped outer face, and a concave-shaped inner face; a fourth lens having a negative refractive power and a concave-shaped inner face; a fifth lens, joined with the fourth lens, and having a positive refractive power, a relatively flat inner face and a convex-shaped outer face; a sixth lens having a positive refractive power, a slightly concave-shaped inner face and a convex-shaped outer face; and a seventh lens, having both convex-shaped inner and outer faces.

Abstract: A compact wide-angle photographic lens system of a retrofocus type includes, from the object side, a first, a sixth, and a seventh meniscus lens group of positive refractive powers, a second and a third meniscus lens group of negative refractive powers, a fourth lens group of a positive refractive power being convex toward an object side, and a fifth cemented lens group of a negative refractive power. The lens system satisfies the conditions, 1.0 f<.vertline.f.sub.(1,2,3,4) .vertline.<2.0 f, f.sub.(1,2,3,4) <0, 0.4 f<d(6)+d(7)<0.6 f, 0.1<f/r(5)<0.2, 0.5<f/r(11)<0.7, 1.65<?n(7)+n(8)!/2<1.75, where f represents a focal length of overall lens system, f.sub.

Abstract: An enlargement lens system with a large working distance comprising five lens components with a stop between the third and fourth components (numbered from the long conjugate side). It includes a first negative lens component, meniscus concave to the stop; a second positive lens component, having a convex surface toward the first lens component; a third and fourth lens component, both cemented negative doublets, meniscus concave to the stop; and a fifth positive power biconvex lens component, wherein BF/EF>1.0, where BF is the short conjugate back focus and EF is the focal length of the lens system.

Abstract: A wide-angle fast lens system includes a front lens group having a negative power, a diaphragm and a rear lens group having a positive power. The front lens group consists of a first sub-lens group and a second sub-lens group having a negative power. The lens system satisfies the following relationships:-0.6<f/f.sub.F <-0.2,6.0<.SIGMA.d.sub.F+S /f<12.0,f/.vertline.f.sub.1a .vertline.<0.07, and0.4<h.sub.aF /h.sub.aL <0.65,wherein "f" represents the focal length of the whole lens system, "f.sub.F " represents the focal length of the front lens group, ".SIGMA.d.sub.F+S " represents the sum of the thickness of the front lens group and the distance between the front and rear lens groups, "f.sub.1a " represents the focal length of the first sub-lens group, "h.sub.aF " represents the height of the paraxial rays incident on the first surface of the first sub-lens group, and "h.sub.aL " represents the height of the paraxial rays incident on the last surface of the first sub-lens group.

Abstract: A wide-angle objective lens is comprised, from the object side, of a first lens component which is a negative meniscus lens having its convex surface facing the object side, a second lens component which is a meniscus lens having its convex surface facing the object side and having positive refractive power, a third lens component which is a cemented meniscus lens comprising a positive lens and a negative lens cemented together and having its convex surface facing the object side and having positive refractive power, a fourth lens component which is a positive meniscus lens having its concave surface facing the object side, and a fifth lens component which is a negative meniscus lens having its concave surface facing the object side. The wide-angle objective lens has a stop disposed between the second lens component and third lens component, and satisfies predetermined conditions.

Abstract: A retrofocus type standard lens includes a front lens group having a positive power, a diaphragm, and a rear lens group having a negative power, in this order from the object side. The focusing is carried out by moving the front lens group without moving the diaphragm and the rear lens group. The front lens group has a negative subgroup and a positive subgroup. The retrofocus type standard lens satisfies the relationships:0.5<f/f.sub.F <1.0;-0.7<f/f.sub.FN <-0.3,wherein "f" designates a focal length of an entire lens system; "f" designates a focal length of the front lens group; and "f.sub.FN " designates a focal length of the negative subgroup.

Abstract: In a wide range of photographing from long shot to close-up, high resolving power and high contrast can be obtained in a wide angle lens system. The wide angle lens system comprises, successively from the object side, a negative meniscus first lens (L1), a junction lens composed of a positive second lens (L2) with a convex surface facing the object and a negative third lens (L3) with a concave surface facing the image, a junction lens composed of a biconvex fourth lens (L4) and a biconcave fifth lens (L5), a positive sixth lens (L6) with a convex surface facing the image, and a negative meniscus seventh lens (L7) with a convex lens facing the image. Also, it satisfies the following conditions (1) to (4):(1) -1.95<F.sub.1 /f<-1.05(2) 1.05<f.sub.23 /f<3.60(3) 1.10<f.sub.45 /f<2.16(4) 1.53<(r.sub.11 +r.sub.10)/(r.sub.11 -r.sub.10)<4.

Abstract: A wide angle lens system comprises a front lens group and a rear lens group having positive refractive power. The front lens group includes in the order from the object side, a negative meniscus lens component having a convex surface facing the object side, a cemented lens component having a negative lens element and a positive lens element and a convex cemented surface facing the object side. The rear lens group includes a cemented lens component having a positive lens element and a negative lens element and a convex surface facing the object side. The rear lens group is moved toward the object side for focusing operation from the infinite object distance to the shortest object distance.

Abstract: A fast lens system is provided which includes a front lens group having a negative power, a diaphragm, and a rear lens group having a positive power, arranged in this order from a side of an object of the lens system. The lens system satisfies the following conditions:-0.5<f/f,<-0.2; (1)1.0<.SIGMA.d.sub.F+S /f<3.0; (2)ana1.5<.SIGMA.d.sub.R /f<3.0, (3)wherein f represents a focal length of the entire lens system, f.sub.F represents a focal length of the front lens group, .SIGMA.d.sub.F+S represents a sum of the thickness of the front lens group and the distance between the front lens group and the rear lens group, and .SIGMA.d.sub.R represents a thickness of the rear lens group.

Abstract: An inverse telescopic wide angle lens comprises a diaphragm; a front lens group of an integral positive or negative refractive power, positioned in the object side in front of the diaphragm and having a first lens group of a negative refractive power including a negative lens of which an image-side air-contacting surface is formed as an aspherical surface concave to the image side, and a second lens group of a positive refractive power positioned between the first lens group and the diaphragm; and a rear lens group of an integral positive refractive power, positioned behind the diaphragm and having plural lenses.

Abstract: A magnifying projecting lens has a negative first lens group, a positive second lens group and a positive third lens group that is arranged in this order from a magnifying side. The lens groups are arranged so as to satisfy the following condition:fb/f>1.7,whereinfb equals a back focus when an object distance is .infin.f equals a focal length of the lens.

Abstract: A wide angle lens system of the retrofocus type is provided which includes two lens units. The first lens unit is of negative power and includes a combination of a positive element having a high dispersion and a negative element having a low dispersion for correction of lateral color. The second lens unit is of positive power and includes a combination of a positive element having a low dispersion and a negative element having a high dispersion for correction of longitudinal color. The lens units satisfy the relationship that the magnitude of f.sub.1 is less than about 1.15 times f.sub.2 and preferably satisfy the relationship that the magnitude of f.sub.1 is less than f.sub.0. The first and second lens units each preferably include an aspheric surface. Applications of the lens system include rear projection television systems wherein a single lens is used to project light from three LCD light valves onto a viewing screen.