Abstract: The invention relates to a stereo imaging unit or system that can have a suitable degree of parallax and a wide angle of view even when used with an image pickup device smaller than film.

Abstract: A fisheye lens with a field angle of at least one hundred sixty degrees is formed of two lens groups, arranged in order from the object side, as follows: a first lens group having negative refractive power and a second lens group having positive refractive power. The first lens group includes, arranged in order from the object side, two lens elements, each having negative refractive power and a meniscus shape with the convex surface on the object side, a lens element having negative refractive power with a concave surface on the image side, and two lens elements of opposite refractive powers. The second lens group includes, arranged in order from the object side, two lens elements of opposite refractive powers, a stop, and two lens elements of opposite refractive powers. The fisheye lens preferably satisfies specified conditions related to spacings of lens surfaces and to distortion characteristics of the fisheye lens.

Abstract: A macro lens comprised of a front lens group of a retrofocus type and a rear lens group of which component lenses are aligned in the order from the closest to the subject.

Abstract: In a lens system, a first lens having negative optical power and a meniscus shape with a convex surface facing an object side, a second lens having positive optical power and a double-convex shape, a third lens having negative optical power and a double-concave shape, a fourth lens having positive optical power, and a fifth lens having positive optical power and a double-convex shape are arranged sequentially from a front side to a rear side. Letting D1,2 be an interval between said first and second lenses, D2,3 an interval between said second and third lenses, bf be a back focus of the entire system, and f be a focal length of the entire system, at least one of three conditions given by 0.6<D1,2/f<1.0, 0.55<D2,3/f<0.85, and 0.9<bf/f<1.1 is satisfied.

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 groups are positioned so that the distance between the negative first lens group and the positive second lens group is set as the maximum distance in the wide-angle lens system. The wide-angle lens system satisfies the following conditions: 2.0<fB/f<2.5??(1) 4.5<f1/f<6.2??(2) 1.8<f2/f<2.0??(3) 1.0<d/f<1.5??(4) wherein fB: the back focal distance of the wide-angle lens system; f: the entire focal length of the wide-angle lens; f1: the focal length of the negative first lens group; f2: the focal length of the positive second lens group; and d: the axial distance between the negative first lens group and the positive second lens group.

Abstract: A retrofocus, wide-angle lens includes a first lens group of negative refractive power, a stop, and a second lens group of positive refractive power. The first lens group includes, in order from the object side, a meniscus lens elements having positive refractive power, two meniscus lens elements having negative refractive power, and a thick lens element. The second lens group includes a cemented lens component that includes a lens element having negative refractive power and a biconvex lens element that is on the object side of a meniscus lens element having negative refractive power with its concave surface on the object side. The second lens group may include a meniscus lens component having positive refractive power on the object side of the biconvex lens element and a meniscus lens component having positive refractive power on the image side of the meniscus lens element having negative refractive power.

Abstract: A projector lens system includes a negative first lens group and a positive second lens group. The first lens group comprises a first lens element that is formed as a negative meniscus lens element, a positive or negative second lens element, a negative third lens element, a positive fourth lens element that is cemented to or separated from the third lens element, and a negative fifth lens element. The first lens group satisfies condition (1) with respect to the refractive power thereof, and satisfies condition (2) with respect to the refractive power of the negative first lens element of the negative first lens group: 0.6<fw/|fI|<1.0(fI<0)??(1) 0.3<fI/f1,1<0.7??(2) wherein fw: focal length of the entire projector lens system at the wide-angle extremity; fI: the focal length of the negative first lens group; and f1,1: the focal length of the negative first lens element of the negative first lens group.

Abstract: A wide-angle lens system having a long back focal length, disposed in front of a ?? CCD camera 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°. The following conditions are met by the first lens group: 1?d/d3<1.2; R3/R2=0.99; and d2/f=0.03. Here, (d) indicates the thickness of the second lens along the normal line at a given distance from the optical axis within the maximum effective diameter of the object side convex surface of the lens. d3 is the thickness of the second lens along the optical axis.

Abstract: An object of the present invention is to provide a fisheye lens, in spite of its compactness, having an angle of view of 180 degrees and a fast f-number of 2.8 with securing sufficient back focal length and suitable for a digital camera. The fisheye lens consists of a front lens group G1 having negative refractive power and a rear lens group G2 having positive refractive power locating with a space along the optical axis apart from the front lens group G1. The front lens group G1 includes a plurality of negative lens components, L1 and L2. The rear lens group G2 includes at least one cemented lens L5, and given conditional expressions are satisfied.

Abstract: A fixed focal length, wide-angle lens includes, in order from the object side, a negative first lens group that includes a plastic negative lens element, a positive second lens group that includes a plastic positive lens element, a positive third lens group that includes a positive lens element joined on its image side to another lens element, and a positive fourth lens group. In the preferred embodiments, all lens groups except the third lens group are single lens elements that each include an aspheric lens surface. Also, the wide-angle lens preferably satisfies specified conditions that, together with the use of plastic lenses, joined lens elements, and aspheric surfaces, enables a high performance, compact, wide-angle lens of relatively simple construction to be produced.

Abstract: A lens (1), a lens (2) and a lens (3) constitute a first group of lenses, a lens (4), a lens (5), a lens (6) and a lens (7) constitute a second group of lenses, and a lens (8) constitutes a third group of lenses in a zoom lens of the present invention. The second group of lenses is constituted by a first positive lens (4), a negative lens (5) which is in a meniscus shape which faces its convex shape toward a side of an object (70), a second positive lens (6) in a meniscus shape which faces its convex shape toward the object (70) side, and the third positive lens (7), which are in order from the object (70) side.

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: A retrofocus, wide-angle lens includes a first lens group of negative refractive power, a stop, and a second lens group of positive refractive power. The first lens group includes, in order from the object side, a meniscus lens elements having positive refractive power, two meniscus lens elements having negative refractive power, and a thick lens element. The second lens group includes a cemented lens component that includes a lens element having negative refractive power and a biconvex lens element that is on the object side of a meniscus lens element having negative refractive power with its concave surface on the object side. The second lens group may include a meniscus lens component having positive refractive power on the object side of the biconvex lens element and a meniscus lens component having positive refractive power on the image side of the meniscus lens element having negative refractive power.

Abstract: The present invention provides a high-performance, thin wide-angle lens suitable for imaging elements with high pixel counts. The wide-angle lens includes, from an object side to an image plane side: a first lens group including a first lens having a negative refractive power and a second lens having a positive refractive power; and a second lens group including a third lens having a negative refractive power, a fourth lens having a positive refractive power, and a fifth lens having a positive refractive power. The fourth lens is bonded to the third lens. The fifth lens is formed with at least one of its convex surfaces being an aspherical surface.

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 large aperture super wide-angle lens system has an angle of view of 2&ohgr;=94° or more, an f-number of about 1.4, small variation in close-range aberrations, compactness, and high optical performance. The lens system includes, in order from an object, a negative lens group GN having negative refractive power which is fixed upon focusing, and a positive lens group GP having positive refractive power as a whole which is moved upon focusing. The positive lens group GP includes a front lens group GF having an aperture stop and a rear lens group GR having positive refractive power. Focusing at a close object is carried out by moving the front lens group GF and the rear lens group GR to the object side with different moving amounts. Prescribed conditional expressions are satisfied.

Abstract: The present invention provides a high-performance, thin wide-angle lens suitable for imaging elements with high pixel counts. The wide-angle lens includes, from an object side to an image plane side: a first lens group including a first lens having a negative refractivity and a second lens having a positive refractivity; and a second lens group including a third lens having a negative refractivity, a fourth lens having a positive refractivity, and a fifth lens having a positive refractivity. The fourth lens is bonded to the third lens. The fifth lens is formed with at least one of its convex surfaces being an aspherical surface.

Abstract: Provided is a retrofocus imaging lens in which various aberrations are satisfactorily corrected, having a sufficient space from a mechanism viewpoint so that a focus group does not interfere with a lens shutter mechanism even at the time of focusing according to a rear-focus system. A retrofocus imaging lens has, in order from an object side, a first lens group and a second lens group. The first lens group is constructed of, in order from the object side, a front-side first lens group having a negative refractive power as a whole and a rear-side first lens group having a positive refractive power as a whole. The first lens group is basically constructed to have a positive refractive power as a whole. The second lens group includes one or more positive lens and one or more negative lens and has a positive refractive power as a whole. Each of the front-side first lens group and the rear-side first lens group includes, basically, one or more positive lens and two negative lenses.

Abstract: A wide-angle lens system includes a negative first lens group, a positive second lens group, a diaphragm, and a positive third lens group. Upon focusing, the positive second lens group moves along the optical axis direction. The negative first lens group includes at least one negative lens element having an aspherical concave surface facing toward the image, and satisfies the following condition: 1.0<X1/f<3.0  (1) wherein X1 designates the distance between the aspherical surface on the optical axis to the diaphragm, and f designates the focal length of the entire wide-angle lens system at an infinite photographing distance.

Abstract: A projection optical system which sufficiently corrects variations in aberrations during focusing irrespective of a distance at which an object is located, i.e. whether the object is located at a point of infinity or at a short distance, while maintaining advantages of a rear focus retrofocus type optical system, is disclosed. This projection optical system has, in order from the enlarging side, a first lens unit having negative optical power, and a second lens unit having positive optical power and moves in a direction of an optical axis for focusing. The following condition is satisfied: 0≦|f/t1|<0.2 where reference character t1 denotes a distance from the reducing-side conjugate plane to a pupil and reference character f denotes a focal length of the entire system.

Abstract: A retrofocus-type lens system comprises, in order of the object side, three lens units wherein the first lens unit serves as the front lens group of negative refractive power and the second lens unit in combination with the third lens unit serves as the rear lens group of positive refractive power. The first lens unit has meniscus lens elements with concave surfaces on the object side. A stop is placed between the front lens group including the meniscus lens elements and the rear lens group including both the second and the third lens units. The lens element on the image side of the first lens unit of the front lens group is of negative power, and the lens element on the image side of the third lens unit is a negative biconcave lens.

Abstract: An objective lens system consisting of a first lens unit having a negative refractive power and a second lens unit having a positive refractive power wherein the first lens unit or the second lens unit comprises at least one radial type gradient index lens element which has a refractive index distribution in a radial direction from an optical axis. This objective lens system favorably corrects chromatic aberration and other aberrations by adequately selecting a value expressing an Abbe's number and a refractive power of medium for the radial type gradient index lens element.

Abstract: In order to provide a large relative-aperture super wide-angle lens having the inclusive angle of 2 &ohgr;=115° or more with the conventional projection method (y=f·tan &thgr;) having the relative-aperture of about F 2.8, having compactness and high optical performance, and having small variation of aberration in relatively close object distance, the lens includes, in order from the object, a divergent lens group Gn having negative refractive power and a convergent lens group Gp having positive refractive power, and the divergent lens group Gn includes at least one aspherical negative lens, and the aspherical lens satisfies predetermined conditional expressions.

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: A large aperture super wide-angle lens system has an angle of view of 2&ohgr;=94° or more, an f-number of about 1.4, small variation in close-range aberrations, compactness, and high optical performance. The lens system includes, in order from an object, a negative lens group GN having negative refractive power which is fixed upon focusing, and a positive lens group GP having positive refractive power as a whole which is moved upon focusing. The positive lens group GP includes a front lens group GF having an aperture stop and a rear lens group GR having positive refractive power. Focusing at a close object is carried out by moving the front lens group GF and the rear lens group GR to the object side with different moving amounts. Prescribed conditional expressions are satisfied.

Abstract: A retrofocus-type lens system comprises, in order of the object side, three lens units wherein the first lens unit serves as the front lens group of negative refractive power and the second lens unit in combination with the third lens unit serves as the rear lens group of positive refractive power. The first lens unit has meniscus lens elements with concave surfaces on the object side. A stop is placed between the front lens group including the meniscus lens elements and the rear lens group including both the second and the third lens units. The lens element on the image side of the first lens unit of the front lens group is of negative power, and the lens element on the image side of the third lens unit is a negative biconcave lens.

Abstract: Compactness of a projection type image display apparatus is realized by achieving miniaturization and wide-angle of a projection lens apparatus while various kinds of aberration are satisfactorily compensated. A first lens group having a negative refracting power, a second lens group having a positive refracting power, and a third lens group having a positive refracting power are positioned in this order, from a screen side, toward an image display element side, in the projection lens apparatus. When f, f1, f3, f23, and fb represent, respectively, a focal length of the whole lens system, a focal length of the first lens group, a focal length of the third lens group, a combined focal length of the second and third lens groups, and a back focus of the whole lens system, the projection lens apparatus satisfies the following conditions: 1.4<|f1|/f  (1) 2.8<f3/f  (2) 3.6<fb/f  (3) 0.1<|f1/f23|<0.3.

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. Furthermore, the a wide-angle lens system satisfies the following conditions: 0.5<H1/H2R<0.9  (1) 1.7<nPAV  (2) 0.5<Xan/Xbn<1.

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 wide-angle lens system includes a negative first lens group, a positive second lens group, a diaphragm, and a positive third lens group. Upon focusing, the positive second lens group moves along the optical axis direction.

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: A wide-angle projection lens is disclosed having three lens groups of negative, positive, and positive refractive power, respectively, in order from the enlarging side, and that favorably corrects both distortion and lateral color. The wide-angle projection lens includes a diaphragm positioned between the second lens group and the third lens group, and is especially suitable for use in a rear-projection-type image display device that uses a multi-display technique wherein multiple projection lenses arranged in an array, with each projection lens displaying image information for a particular segment of the image to be displayed. By satisfying specified conditions, the wide-angle projection lens, when used in a projection-type image display device, enables the image display device to be more compact.

Abstract: A lens system has the first and second lens components from the object side. The first lens component has a negative optical power. The second lens component has a positive optical power. The lens system fulfills the conditions: 0.0<PRL/Y′<0.5, 0.5<Pf/f<1.0. In the conditions, PRL represents a distance in a direction perpendicular to the optical axis between the optical axis and an incident position where a lower ray of a most off-axial rays enters said second lens component, Y′ represents a largest image height, f represents a focal length of the entire lens system, and Pf represents a focal length of said second lens component.

Abstract: Provided is a retrofocus imaging lens in which various aberrations are satisfactorily corrected, having a sufficient space from a mechanism viewpoint so that a focus group does not interfere with a lens shutter mechanism even at the time of focusing according to a rear-focus system. A retrofocus imaging lens has, in order from an object side, a first lens group and a second lens group. The first lens group is constructed of, in order from the object side, a front-side first lens group having a negative refractive power as a whole and a rear-side first lens group having a positive refractive power as a whole. The first lens group is basically constructed to have a positive refractive power as a whole. The second lens group includes one or more positive lens and one or more negative lens and has a positive refractive power as a whole. Each of the front-side first lens group and the rear-side first lens group includes, basically, one or more positive lens and two negative lenses.

Abstract: The invention relates to a large-apertured microlithography projection lens. The diaphragm error is also systematically corrected, so that the pupil plane is slightly curved and the lens can be stopped down without comprising quality. The system diaphragm of the projection lens is located in the area of the last lens cluster of positive refractive power on the image side. The telecentrics of the projection lens remain stable on the image side during stopping down.

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. The wide-angle lens system satisfies the following conditions: 0.5<TL2/f<1.0  (1) 4<f1/f2<−2  (2) wherein TL2 designates the distance, in the second lens group, between the most object-side surface of the most object-side lens element and the most image-side surface of the most image-side lens element; f designates the focal length of the entire lens system when an object at an infinite distance is in an in-focus state; f1 designates the focal length of the first lens group; and f2 designates the focal length of the second lens group.

Abstract: A retrofocus lens system comprises a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power. The first lens group includes a first lens, a meniscus-shaped second lens having a negative power and a convex surface facing the large conjugate side, a third lens having a negative power, and a fourth lens. The second lens group includes a fifth lens having a positive power. The third lens group includes a sixth lens having a negative power, both surfaces of which are concave, a seventh lens having a positive power, both surfaces of which are convex, an eighth lens having a positive power, both surfaces of which are convex, and a ninth lens having a positive axial power. The system satisfies 0.9<f2/f3<1.8, 1.5<|f1|/f<2.

Abstract: A projection lens having a first lens group of negative refractive power and a second lens group of positive refractive power, in order from the enlarging side of the projection lens. A stop is positioned within a specified distance of the projection lens element surface nearest the reducing side. The second lens group consists of four lens elements of positive, positive, negative, and positive refractive power, in order from the enlarging side. Specified conditions are preferably satisfied in order to make the projection lens compact and to ensure that various aberrations are favorably corrected.

Abstract: A wide-angle projection lens is disclosed having three lens groups of negative, positive, and positive refractive power, respectively, in order from the enlarging side, and that favorably corrects both distortion and lateral color. The wide-angle projection lens includes a diaphragm positioned between the second lens group and the third lens group, and is especially suitable for use in a rear-projection-type image display device that uses a multi-display technique wherein multiple projection lenses arranged in an array, with each projection lens displaying image information for a particular segment of the image to be displayed. By satisfying specified conditions, the wide-angle projection lens, when used in a projection-type image display device, enables the image display device to be more compact.

Abstract: In order to provide a large relative-aperture super wide-angle lens having the inclusive angle of 2&ohgr;=115° or more with the conventional projection method (y=f·tan &thgr;) having the relative-aperture of about F 2.8, having compactness and high optical performance, and having small variation of aberration in relatively closed object distance, the lens includes, in order from the object, a divergent lens group Gn having negative refractive power and a convergent lens group Gp having positive refractive power, and the divergent lens group Gp includes at least one aspherical negative lens, and the aspherical lens satisfies predetermined conditional expressions.

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 the object. The wide-angle lens system satisfies the following condition: −1.4<f1/f<−1.1  (1) wherein f1 designates the focal length of the first lens group, and f designates the focal length of the entire lens system.

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 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 wide-angle zoom lens system having a short optical total length not only at the wide-angle end but also at the telephoto end and a reduced telephoto ratio despite the fact that it has a high zoom ratio, with a view to achieving a reduction in size of cameras. The zoom lens system has a first lens unit G1 of positive refractive power, a second lens unit G2 of negative refractive power, a third lens unit G3 of positive refractive power, and a fourth lens unit G4 of negative refractive power. When the zoom lens system is zoomed from the wide-angle side to the telephoto side, each of the lens units moves toward the object side such that the space between the first lens unit G1 and the second lens unit G2 increases, whereas the space between the third lens unit G3 and the fourth lens unit G4 decreases.

Abstract: A retrofocus lens system has a negative first, a positive second and a positive third lens group. The first lens group includes an aspheric first lens, a negative meniscus second and third lenses that are convex on the large conjugate side, and a negative meniscus fourth lens being convex on the small conjugate side. The second lens group includes a positive fifth lens and a sixth lens joined to the fifth lens. The third lens group includes a positive meniscus seventh lens being convex on the small conjugate side, a biconcave eighth lens, a positive ninth lens joined to the eighth lens, a biconvex tenth and eleventh lenses, and an aspheric twelfth lens. The system satisfies 0.8<f2/f3<1.5, 1.6<|f1|/f<2.

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 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 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.