Abstract: A photographic lens system composed of a negative first lens group, a diaphragm, and a positive second lens group, in this order from the object side. The second lens group has a positive meniscus lens element having a convex surface facing the image side, a cemented sub-lens group having a positive lens element and a negative lens element, and a positive single lens element, in this order from the object side, wherein the photographic lens system satisfies the following conditions:1.5<.vertline.f.sub.1 .vertline./f<5.0 (1)1.1<f.sub.2 /f<2.0 (2)0.6<D.sub.AS /f.sub.2 <1.2 (3)whereinf designates the focal length of the entire optical system;f.sub.1 designates the focal length of the first lens group;f.sub.2 designates the focal length of the second lens group;D.sub.AS designates the distance from the diaphragm to the first principal point of the second lens group.

Abstract: The invention provides an inexpensive phototaking lens system comprising a reduced number of lenses, which makes use of a diffractive optical element to make correction for first-order longitudinal chromatic aberration and chromatic aberration of magnification, and eliminates higher-order chromatic aberrations of magnification produced in a wide-angle lens system. The phototaking lens system comprises a front group having negative power, an aperture stop and a rear group having positive power, with the rear group comprising at least one positive lens and a diffractive optical element having a diffractive surface D of positive power, and satisfies conditions for making good correction for chromatic aberrations produced at a refractive system with the diffractive optical element and conditions for making well-balanced correction for longitudinal chromatic aberration and chromatic aberration of magnification.

Abstract: A retrofocus projection lens system comprising, in order from a large conjugate side a first lens group having a negative refracting power and including a plurality of lenses, a second lens group having a positive refracting power, and a third lens group having a positive refracting power and including a plurality of lenses. The lens of the first lens group which is nearest to the large conjugate side is an aspherical lens, and the lens of the third lens group which is nearest to a small conjugate side is an aspherical lens. The retrofocus projection lens system desirable satisfy the following conditional expressions (1) to (3):1.8<D.sub.1 /f<3.0 (1)1.1<f.sub.2 /f.sub.3 <1.6 (2)1.5<.vertline.f.sub.1 .vertline./f<2.3 (3)where a symbol f.sub.1 designates a focal length of the first lens group, a symbol f.sub.2 designates a focal length of the second lens group, a symbol f.sub.

Abstract: An eyepiece lens is disclosed, in which the total number of constituent lenses is reduced but good optical performance is obtained by setting forth proper rules of design for optical parameters.

Abstract: Negative, positive, and positive lens groups are disposed successively from the larger conjugate length side, and focal length adjustment is effected by the convex lens disposed on the smallest conjugate length side of the first lens group, thereby yielding a long back focus and a telecentric characteristic, decreasing distortion and chromatic aberration, and simplifying the focusing structure. Successively from the larger conjugate length side, a first lens group G.sub.1 having a negative refracting power and including a convex lens L.sub.5 disposed on the smallest conjugate length side, a second lens group G.sub.2 having a positive refracting power and causing a luminous flux diverged by the first lens group G.sub.1 to become substantially afocal, and a third lens group G.sub.3 having a positive refracting power are disposed, and the convex lens L.sub.5 disposed on the smallest conjugate length side of the first lens group G.sub.1 is moved on an optical axis so as to effect focus adjustment.

Abstract: A super-wide angle lens, sequentially from an object side, comprises a first negative lens L1, a second negative lens L2, and a third positive lens L3. The first negative lens L1 with its concave surface toward an image side has an image-side surface with a curvature larger than that on an object-side surface. The second negative lens L2 is disposed at a predetermined spacing from the first negative lens L1 and takes a negative meniscus shape with its convex surface toward the object side. The third positive lens L3 has its convex surface toward the object side.

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: The invention provides an inexpensive wide-angle lens system which is well corrected for longitudinal chromatic aberration and chromatic aberration of magnification without recourse to any anomalous dispersion glass while a long enough back focus is fully ensured. The wide-angle lens system comprises a front lens group comprising at least one positive lens and having negative power as a whole, an aperture stop 10, and a rear lens group comprising at least one negative lens and a diffractive optical element 11 having a diffractive surface of positive power, and having positive power as a whole, and satisfies 0.005<f/f.sub.DOE <0.03 where f is a focal length of the wide-angle lens system and f.sub.DOE is a focal length of the diffractive surface provided that f.sub.DOE is free of power of a substrate.

Abstract: Variable focal length lens system comprises two adjacent lens units, one stationary, the other movable. These lens units are in order from an object side towards an image side(i) A first lens unit possessing divergent refractive power. The first lens unit is the front most lens unit. It consists of a single negative lens component.(ii) A second lens unit possessing convergent refractive power. The second lens unit, includes at least two positive power lens components and an aperture stop.

Abstract: This invention relates to a compact wide-angle lens which consists of five members. The first member and the last member are each divergent lenses of low deviation, which consist of low refractivity crown glass. The second member and the third member are convergent lenses made of high refractivity crown glass. The fourth member, which is the final member of the lens according to the invention, consists of a convergent lens and a divergent lens which are cemented to each other. Type of glass are used for this cemented member which have a very low difference in refractive index but a very high difference in dispersion. The convergent lens has a low dispersion and the divergent lens has a high dispersion. One of the two glass/air surfaces of the cemented member is aspherical. A lens such as this according to the invention has a maximum aperture ratio of at least 1:5.6 and an image angle of 105.degree.. The chromatic correction is well defined and is very substantially independent of the distance of the object.

Abstract: A retrofocus type super wide angle lens system includes a front lens group of negative power and a rear lens group of positive power, arranged in this order from the object side. The front lens group consists of a negative meniscus first lens element with a convex surface facing the object side and a second lens element having at least one aspherical surface, arranged in this order from the object side. The aspherical second lens element is shaped such that it forms a biconcave lens in the vicinity of the optical axis and forms a negative meniscus lens with a convex surface located on the object side at a peripheral portion thereof.

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 retrofocus type lens uses a rear focus method that provides high image forming performance. A retrofocus type lens includes, from an object side, a first lens group G.sub.1 having negative refractive power, which has a negative meniscus lens component L.sub.A having a convex surface facing an object side and a positive lens component L.sub.8 positioned closer to the image side than the negative meniscus lens component L.sub.A. At least one surface among all of the lens surfaces of the first lens group G.sub.1 is aspheric. A second lens group G.sub.2 is provided and has positive refractive power. The second lens group G2 has, from the object side, a front group G.sub.2F and a rear group G.sub.2R having positive refractive power. Focusing on a near object point is accomplished by moving the front group G.sub.2F and the rear group G.sub.2R of the second lens group with different moving amounts. When the moving amount of the front group G.sub.2F and the rear group G.sub.

Abstract: The invention provides a solution to a problem of allowing a symmetrical wide-angle lens system to have a large aperture ratio, and achieves an optical system which is well improved in terms of sagittal coma and curvature of field, and has a satisfactory vignetting factor as well. The optical system comprises basically a first lens group G1 having a negative refracting power, a second lens group G2 containing an aperture stop and having a positive negative power, and a third lens group having a negative refracting power. The second lens group G2 is divided into front and rear sub-groups G.sub.21 and G.sub.22, each having a positive refracting power, between which the aperture stop is located. The first lens group G1 comprises at least one negative meniscus lens convex on an object side; the front sub-group G.sub.21 of the second lens group comprises at least one set of cemented lens including a positive lens and a negative lens; and the rear sub-group G.sub.

Abstract: The invention proves a compact and simple wide-angle lens system composed of a reduced number of lenses and having high productivity, which is well suited for use on digital cameras, while making sure of the space necessary for edge, and middle thicknesses, and constructing the system and, at the same time, having a given back focus and exit pupil position, and sufficient image-forming capability, and which comprises two lens groups or, in order from the object side thereof, a negative lens group GN and a positive lens group GP with an aperture stop D midway between them and a lens located nearest to the object side thereof being defined by a positive lens, said positive lens conforming to three conditions in terms of focal length, shape factor, and ensuring sufficient edge thickness.

Abstract: A retrofocus type lens includes a front lens group including at least one negative lens and a rear lens group provided nearer than the front lens group to an image side, including at least two positive lenses and a negative lens. A positive lens of the rear lens group which is closest to an object side, is made of glass. Lenses of more than half of lens elements are made of plastic, and satisfy the following conditional expression,0.7<f.sub.G /f<4.0where f.sub.G represents a focal length of the positive lens of the rear lens closest to an object side, and f represents a focal length of an entire optical system.

Abstract: A wide-angle lens system includes a first, second, third and fourth lens components which are arranged in this order in a direction from an object side to an image surface side along an optical axis. A stop is provided between the second lens component and the third lens component. The first lens component comprises a double-concave lens, the first lens component having a first refracting power .phi.1 which is negative. The second lens component comprises a positive lens and a negative lens which are arranged in this order in the direction, the second lens component having a second refracting power .phi.2 which is positive. The third lens component comprises a negative lens, a positive lens and a negative lens which are arranged in this order in the direction, the third lens component having a third refracting power .phi.3 which is positive. The fourth lens component comprises a negative lens, the fourth lens component having a fourth refracting power .phi.4 which is negative.

Abstract: A retrofocus lens system comprises, in order from a large conjugate side: a first lens group having a negative refracting power and including a plurality of lens elements; a second lens group having a positive refracting power; and a third lens group having a positive refracting power. Each of the lens elements of the first lens group has a negative refracting power. Following conditional expressions (1) to (3) are satisfied:1.3<D.sub.1 /f<1.8 (1)0.7 <f.sub.2 /f.sub.3 <1.1 (2)1.1 <.vertline.f.sub.1 .vertline./f<1.6 (3)where D.sub.1 is air gap between the first lens group and the second lens group, f.sub.1 is a focal length of the first lens group, f.sub.2 is a focal length of the second lens group, f.sub.3 is a focal length of the third lens group, and f is a focal length of whole lens system including the first to third lens groups.

Abstract: An imaging lens system consisting of a front lens unit which comprises a negative lens component disposed on the image side and has a positive refractive power, and a rear lens unit which is composed of a positive lens component: a distance ffb as measured from an object side surface of the rear lens unit to a front focal point of the rear lens unit, a distance D as measured from an exit pupil of the front lens unit to an object side surface of the rear lens unit, and refractive powers of the front lens unit and the rear lens unit being adequately defined for the imaging lens system.

Abstract: A wide angle lens comprises in order from the object end an aperture stop, a first meniscus lens .sub.L1 having a convex object end surface and a second positive power lens element L.sub.2, the lens satisfying the following conditions:-0.10<f.sub.2 /f.sub.1 <0.74.0<f/R.sub.1 <7.50<f/R.sub.3 <1.60.01<D/f<0.22where f.sub.1, f.sub.2 and f are the focal length of the first lens L.sub.1, the second lens L.sub.2 and the overall lens system, respectively, R.sub.1 and R.sub.3 are the radii of the object end surfaces of the first and second lenses L.sub.1 and L.sub.2, respectively, and D is the axial distance between the object end surface of the first lens L.sub.1 and the image plane.

Abstract: A wide angle objective system is described for, inter alia CCD cameras, which system is compact, inexpensive and satisfactorily corrected. It comprises a front meniscus lens (L.sub.1), a thick convex-concave central lens element (L.sub.2) and a biconvex lens element (L.sub.3), the two last-mentioned elements preferably being cemented together, the pupil (P) being present at the area of the exit surface (4) of the second lens element and the first and the third element (L.sub.1,L.sub.3) being made of, for example PMMA and the second element (L.sub.2) being made of, for example PC.

Abstract: A reverse telephoto lens includes a front negative group of lens components having a front component with greater than normal separation from a rear positive group of lens elements. Preferably, the front negative group also includes a rear positive component that is meniscus concave to the front.

Abstract: A Keplerian zoom finder optical system comprises an objective lens group having a positive refracting power on the whole and constructed of, in order from an object side, a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, a third lens unit having a negative refracting power and a fourth lens unit having a positive refracting power. This finder also comprises a regulating element, disposed in the vicinity of a focal position of the objective lens group, for regulating a visual field. The finder further comprises an eyepiece unit having a positive refracting power. The finder varies a magnification by moving at least the second lens unit along an optical axis and satisfies the following condition:-5<f.sub.3 /f.sub.w <-3wheref.sub.w : the synthetic focal length of the first and second lens units in a minimum magnification state, andf.sub.3 : the focal length of the third lens unit.

Abstract: An objective lens device comprising in order from the lens closest to an object side, a negative meniscus first lens whose concave side faces the object side; a positive second lens; a positive meniscus third lens whose convex side faces an image side; a negative meniscus fourth lens whose concave side faces the object side; a negative meniscus fifth lens whose convex side faces the object side; and a positive sixth lens. The fifth and sixth lenses are cemented together to form a cemented lens subunit. The objective lens device contains six lenses in its entire lens structure, has a long back focus, and provides excellent optical properties over an entire field.

Abstract: A wide angle lens is constituted by four sheets of concave, concave, convex, and convex lenses successively arranged from the object side so as to satisfy predetermined conditional expressions concerning focal lengths, whereby various kinds of aberration are favorably corrected and, while the cost required for molding each lens is minimized, a higher brightness can be obtained as compared with the conventional wide angle lens. From the object side, first, second, third, and fourth lenses (L.sub.1 to L.sub.4) are successively disposed. Each of the first lens (L.sub.1) and second lens (L.sub.2) is made of a negative meniscus lens whose concave surface with a stronger curvature is directed toward the imaging surface (1), while each of the third lens (L.sub.3) and the fourth lens (L.sub.4) is made of a biconvex lens whose surface with a stronger curvature is directed toward the imaging surface (1), such that f.sub.2 /f.sub.1 is 0.888 thereby satisfying a conditional expression of 0.8<f.sub.2 /f.sub.1 <1.

Abstract: A high-performance taking lens system suitable for a lens shutter type camera, which is capable of displaying superior optical performance as far as the edges of film image field with minimal deterioration of the performance despite a simple arrangement. The taking lens system has a front lens unit including at least one positive lens (G1) and at least one negative lens (G2) whose image-side surface has a higher curvature than that of the object-side surface thereof, and a rear lens unit disposed behind the front lens unit and including a doublet (G3) which consists of one positive lens and one negative lens and which has a positive refractive power, and a positive lens (G4). The lens surface of the doublet (G3) that is the closest to the image side is concave toward the image side. The intermediate lens surface of the doublet (G3) is convex toward the image side. The negative lens (G2) is preferably a meniscus negative lens having a concave surface directed toward the image side.

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 retro-focus-type lens is provided from a large conjugate side with a first lens group having a negative refracting power, a second lens group having a positive refracting power which is spaced away from the first lens group at an air interval D1, and a third lens group having a positive refracting power. The following conditions are satisfied when focal lengths of the first lens group, the second lens group, the third lens group, and a total lens system are assumed respectively as f1, f2, f3, and f:1.8<D1/f<3.01.1<f2/f3<1.61.5<.vertline.f1.vertline./f<2.3.A projection lens constructed by inserting a mirror in a lens system of thus constructed retro-focus type lens is used in a projection-type display apparatus.

Abstract: An observation optical system for endoscopes configured so as to allow observation of objects located in liquids, comprising an objective lens system and relay lenses for relaying an image formed by the objective lens system, and satisfies the following conditions (1) and (2):0.08.ltoreq.N.sub.w .multidot.f tan [sin.sup.-1 {(1/N.sub.w) sin .theta..sub.Al }]/I.sub.1 .ltoreq.1.18 (1)0.9.ltoreq.N.sub.w .multidot.f.multidot.tan[sin.sup.-1 {(1/N.sub.w) sin .theta..sub.A0.5 }]/I.sub.0.5 .ltoreq.1.1 (2)wherein the reference symbol f represents a focal length of the objective lens system, the reference symbol N.sub.w designates a refractive index of a liquid, the reference symbols .theta..sub.Al and .theta..sub.A0.5 denote field angles at the maximum image height and a half of the maximum image height in water respectively, and the reference symbols I.sub.1 and I.sub.0.5 represent a maximum image height and a half of the maximum image height.

Abstract: A single focal length lens system has a first negative lens element and a last negative lens element. The first negative lens element is disposed at an object side end of the lens system and the object side surface thereof is concave. The last negative lens element is disposed at an image side end of the lens system. The lens system fulfills the following condition: ##EQU1## wherein .phi.f represents the refractive power of the first negative lens element; and .phi.1 represents the refractive power of the last negative lens element.

Abstract: An optical system of a projection display apparatus includes a projection lens assembly having a first lens group having a negative power, a second lens group having a negative power and a third lens group having a positive power, all arranged in this order from a side of a screen. An air space is provided between the first and second lens groups and also between the second and third lens groups. Each air space is longer than the entire length of the second lens group as taken along the optical axis of the assembly.

Abstract: An inverse telescopic wide angle lens comprising: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; anda rear lens group of an integral positive refractive power, positioned behind the diaphragm and having plural lenses;wherein the rear lens group includes a movable lens group consisting of plural lenses which are integrally moved for focusing, wherein the front lens group is fixed, and the focusing is conducted by the movement of the movable lens group alone in such a manner as to vary the rear focal length between the movable lens group and the image plane.

Abstract: An inverse telephoto large aperture wide angle lens comprises a first lens group with a negative refractive power, a second lens group with a positive refractive power, a stop, a third lens group with a negative refractive power, and a fourth lens group with a positive refractive power arranged in the named order from a side of an object, in which for focusing on a near object from infinity the first lens group is fixed with respect to an image surface, and the second, third, and fourth lens groups are moved along an optical axis thereof toward the object such that a space between the first lens group and the second group and a space between the second lens group and the third lens group decrease, but a space between the third lens group and the fourth lens group increases.

Abstract: A fixed-focal-length lens system includes first and second lens groups arranged in order from front to rear. The first lens group consists of a plurality of lenses and has a negative refracting power and the second lens group consists of a plurality of lenses and has a positive refracting power. The fixed-focal-length lens system satisfies the following conditions0.58<.vertline.f.sub.1 /f.vertline.<0.95 (1)0.50<.vertline.f.sub.1 /f.sub.2 .vertline.<1.0 (2)1.6<Bf/f<2.9 (3)1.1<f.sub.2 /f<1.45 (4)wherein f represents the focal length of the fixed-focal-length lens system, f.sub.1 represents the focal length of the first lens group, f.sub.2 represents the focal length of the second lens group and Bf represents the back focus of the lens system.

Abstract: A retrofocus type lens having a plurality of lenses divided into three lens units, or, in the order from a screen, a first lens unit, a second lens unit and a third lens unit, wherein letting the focal length of the entire lens system be denoted by fT, and the distance from a lens surface on the side of an original image to the original image by SK,SK>0.7 fTis satisfied, and the second lens unit and the first lens unit or the third lens unit each is provided with at least one aspherical lens of which at least one of the lens surfaces is aspherical.

Abstract: A retrofocus type lens includes, in order from the screen side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power with a longest air separation in the lens system left therebetween, wherein a lens positioned closest to the screen side in the second lens unit is formed to a meniscus positive lens convex toward the screen side.

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: An air spaced reverse telephoto objective lens for use in a laser chemical vapor deposition system or the like having a quartz plate window. The objective lens includes a negative component having a first air-spaced doublet wherein each doublet element is made of crown glass and a negative meniscus crown glass element spaced from said first air-spaced doublet. The objective lens further includes an aperture stop, a positive component including second and third doublet components for effecting color correction, and a pair of bi-convex elements for effecting spherical aberration correction. The objective lens provides a common focal plane for both illuminating light and laser light passing through the objective lens and the quartz plate window.

Abstract: A retro-focus wide-angle lens system having, in order from the object side, a negative power front group and a positive power rear group having a diaphragm stop. The front group comprises a positive first lens element and a negative meniscus second lens element having a convex surface directed towards the object. The rear group comprises a positive third lens element, a negative fourth lens element having an aspheric surface and a positive fifth lens element. The negative power of the fourth lens element increases toward the outer edge.

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.

Abstract: A lens system is provided which includes two lens units. The first lens unit includes two meniscus lenses whose concave surfaces face each other and the second lens unit has a positive power. The system can be configured to have a wide field of view and/or to be telecentric. In its basic form, a well-corrected lens having a relatively large aperture and field of view is achieved through the use of only three lens elements.

Abstract: A zoom lens system comprising, in the order from the object side, a front lens unit having a negative refractive power as a whole and a rear lens unit having a positive refractive power as a whole; and said rear lens unit comprising a first positive lens element, a second positive lens element having a convex surface on the image side, a third biconcave lens element and a fourth biconvex lens element, and the second lens element and the third lens element being cemented to each other so as to compose a cemented doublet, adapted so as to perform variation of focal length by varying the airspace reserved between said front lens unit and said rear lens unit.

Abstract: A behind stop wide angle lens system comprises a negative meniscus lens L.sub.1 having a convex surface directed to the object, a positive meniscus lens L.sub.2 having a convex surface directed to the object, a double-side-concave negative lens L.sub.3 having both surfaces concaved, a double-side-convex positive lens L.sub.4 having both surfaces convexed, and a stop S. These lenses are arranged in the mentioned order from the end adjacent the object. The lenses satisfying the following conditions (1) to (4):-2.8f<f1<-1.3f (1)0.7f<f2<0.82f (2)1.5<r1/r2<2.3 (3)0.13<r3/r4<0.4 (4)wherein f represents the focal distance of the whole lens system, f1 represents the focal distance of the negative meniscus lens L.sub.1, f2 represents the focal distance of the positive meniscus lens L.sub.2, r1 and r2 respectively represent the radii of curvature of the object-side surface and the image-side surface of the negative meniscus lens L.sub.