Abstract: A zoom lens system has, from the object side, a first lens unit having a positive optical power and a second lens unit having a negative optical power. The second lens unit is provided at the image side of said first lens unit with a variable air space formed between said first and second lens units. The zooming from the shortest focal length condition to the longest focal length condition is performed by decreasing said variable air space. The zoom lens system fulfills the following conditions:tan .omega.W.gtoreq.0.7 ##EQU1## where, .omega.W represents a half angle of view in the shortest focal length condition;fT represents a focal length of the entire zoom lens system in the longest focal length condition; andTLW represents a total length of the entire zoom lens system (a distance between a summit of the most object side surface of the entire lens system and the image plane).

Abstract: An inexpensive, compact, high performance zoom lens which has excellent production adaptability is disclosed. The zoom lens has a front lens group of positive refractive power which includes a negative lens element having a concave aspheric surface on the object-side, and a positive lens element having a convex surface on the image-side. The rear lens group consists of a negative lens element. A stop is arranged between the negative lens element and the positive lens element in the front lens group, and the following conditional formulas (1)-(3) are satisfied:0.40<f.sub.2 /f.sub.w <0.50 (1)0.01<D.sub.2 /f.sub.w <0.05 (2)-0.20<R.sub.4 /R.sub.3 <0.0 (3)wheref.sub.2 is the focal distance of the positive lens element in the front lens group,f.sub.w is the focal distance of the zoom lens at the maximum wide-angle state,D.sub.2 is the distance between the acing surfaces of the negative lens element and the positive lens element in the front lens group,R.sub.

Abstract: A compact zoom lens system includes, when viewed from an object side, a first lens group with positive refractive power and a second lens group. The magnification of the system can be changed by varying a distance between the first lens group and the second lens group, wherein the following condition is satisfied:Lt/ft<0.78wherein:Lt is the distance between the surface of lens closest to the object and the image plane; andft is the focal length of the zoom lens system.

Abstract: A compact two-group zoom lens, wherein zooming is accomplished by changing the distance between the two lens groups. In order from the object side, the first lens group G1 is of positive refracting power and includes a negative meniscus lens element L.sub.1 with its concave surface on the object side, a positive meniscus lens element L.sub.2 made of plastic having two aspherical surfaces with its convex surface on the object side, and a biconvex lens element L.sub.3 having different surface curvatures, with its surface of stronger curvature on the image side. The second lens group G2 includes a positive meniscus lens element L.sub.4 that has two aspherical surfaces with its concave surface on the object side, and a negative meniscus lens element L.sub.5 with its concave surface on the object side. It is preferable that lens element L.sub.4 has an aspherical surface of positive refracting power and lens element L.sub.2 has an aspherical surface of negative refracting power.

Abstract: A zoom lens system is composed of two lens units. The first lens unit is arranged at an object-side end and the second lens unit is arranged at an image-side end. The first lens unit has one lens element of a positive refractive power. The second lens unit has two lens elements. One is an aspherical plastic lens of non-refractive power. The other is a lens having a negative refractive power. During zooming from a wide angle end to a telephoto end, the distance between the first and second lens units is decreased.

Abstract: A zoom lens system having two lens group. The zoom lens system has a zooming ratio greater than 2.4, a viewing angle of over 70 degrees and a telephoto ratio of about 1.0. The zoom lens system includes a first lens group of a positive refractive power, which has four lenses, and a second lens group of a negative refractive power, which has three lenses. The second lens group includes one aspherical lens surface. The zoom lens system according to the present invention satisfies the following conditions:0.22<fl/ft<0.302.45<ft/fw0.74<Ll1/(ft-fw)<0.850.75<fl/Y<1.10wherefl is a focal length of a first lens group;ft is a focal length of the entire zoom lens system at a telephoto position;fw is a focal length of the entire zoom lens system at a wide angle position;Ll1 is a shift distance of the first lens group during zooming; and2Y is a diagonal length of an image.

Abstract: A compact zoom lens system includes a positive first lens group and a negative second lens group. The first lens group includes a first positive lens, a second negative biconcave lens and a third positive biconvex lens. The second lens group includes a fourth positive meniscus lens with the concave surfaces of the lens oriented towards the object side and a fifth negative meniscus lens with the concave surfaces of the lens oriented towards the object side. The zoom lens system satisfies the following conditions:0.40<f1/f.sub.W <0.60where f1 represents a focal length of the first lens, and f.sub.W represents a focal length of the zoom lens system at a wide angle position.

Abstract: A high performance zoom lens with a high zoom ratio is suitable for a wide range of uses. The zoom lens includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and the fifth lens group having a positive refractive power. A magnification of the second lens group, a magnification of the third lens group and a magnification of the fourth lens group almost simultaneously attain near equal magnification. The zoom lens system satisfies at least one predetermined condition.

Abstract: A zoom lens system has a plurality of lens units. Zooming is performed by varying distances between the lens units. A gradient index lens is included in the lens units. The gradient index lens has a gradient index in a direction vertical to an optical axis. The gradient index lens has at least one aspherical surface.

Abstract: An achromatic lens system comprising a front lens group, a diffraction lens and a rear lens group, in this order from the object side, wherein; the front lens group is provided with a frontmost convex surface on the object side and a rearmost concave surface on the image side; the rear lens group is provided with a rearmost convex surface on the image side; the front and rear lens groups are arranged to generate under-axial chromatic aberration for blue light and generate over-axial chromatic aberration for red light, with respect to green light that is considered the reference light; and, achromatic correction of light in the visible region is conducted by correcting the axial chromatic aberrations with a diffracting function of the diffraction lens.

Abstract: A zoom lens system includes a positive lens unit and a negative lens unit. Focusing in a focal length range from a shortest focal length condition to a middle focal length condition is performed by moving the positive lens unit, and focusing in a focal length range from the middle focal length condition to a longest focal length condition is performed by moving the negative lens unit. The zoom lens system fulfills the following condition: ##EQU1## where B.sub.f is a distance from a rear end surface of the zoom lens system to a film at the shortest focal length condition and .increment.t is a diagonal length of the film.

Abstract: A zoom lens, comprises a first lens group, provided in an object side, having a positive refracting power; and a second lens group, provided in an image side from the first lens group, having a negative refracting power; wherein the zoom lens changes magnification by changing a distance between the first and second lens groups, the first lens group comprises a 1a lens subgroup having a negative refracting power, a diaphragm and a 1b lens subgroup having a positive refracting power all arranged in such the order from the object side to the image side; and the zoom lens satisfies the following conditions:0.7<L/f.sub.T <1 (1)2.0<f.sub.T /f.sub.1 <4.2 (2)0.1<f.sub.1 /.vertline.f.sub.1a .vertline.<0.6 (3)in which L represents a distance between the image focal point of the zoom lens and an object side surface of the first lens group at a telephoto end position, f.sub.T represents a focal length of the zoom lens at the telephoto end position, f.sub.

Abstract: A zoom lens system comprises a first lens group of positive power and a second lens group of negative power. The zoom lens system is arranged to perform a zooming operation by varying a distance between the first lens group and the second lens group. Furthermore, the first lens group comprises a front sub lens group of negative poser and a rear sub lens group of positive power. Still further, the front sub lens group comprises a first single lens element of negative power and a second single lens element having an aspherical surface on which the radius of curvature becomes larger in the off-axis region, and the rear sub lens group of the first lens group comprises a cemented lens having a positive lens element and a negative lens element. Moreover, the zoom lens system satisfies various conditions.

Abstract: The invention comprises a zoom lens system including two lens groups. The first lens group has an overall positive refractive power, and includes three sub-group lens units. The first sub-group lens unit has a negative refractive power, the second sub-group lens unit has a positive refractive power, and the third sub-group lens unit has a positive refractive power. The second lens group has an overall negative refractive power and includes two sub-group lens units. The fourth sub-group lens unit has a positive refractive power, and the fifth sub-group lens unit has a negative refractive power. The magnification of the system can be changed by varying a distance between the first lens group and the second lens group, wherein the following conditions are satisfied:Mt/Mw>1.95,0.20<fbw/fw<0.

Abstract: A zoom lens system of the present invention comprises, from the object side, a front lens unit having a positive refractive power and a rear lens unit having a negative refractive power, and performs zooming by changing the spatial distance between the front lens unit and the rear lens unit. The rear lens unit comprises, from the object side, a positive lens and a negative lens, at least one surface of said positive lens being aspherical and the Abbe number and refraction factor of said positive lens being set appropriately.

Abstract: A zoom lens system includes, from the object to image side, a first lens unit of a positive refractive power having a first lens element with a power to both diffract and refract light. A second lens unit has a negative refractive power and may include a second lens element having both the power to diffract and refract light, and it least a third lens unit is included. A zooming operation is performed by varying the distances between the respective first, second, and third lens units.

Abstract: In a compact wide-angle zoom lens having a two-group configuration composed of positive and negative lens groups, each lens is set to have a predetermined form and satisfy a predetermined range of conditional expression, thereby attaining a high brightness at its wide-angle end, a large angle of view, and a small lens thickness at its telephoto end. The first lens group comprises a biconcave negative first lens L.sub.1 ; a cemented lens composed of a negative second lens L.sub.2 and a biconvex positive third lens L.sub.3 ; and a biconvex positive fourth lens L.sub.4. The second lens group comprises a fifth lens L.sub.5 having an aspheric surface; a sixth lens L.sub.6 having a positive meniscus form with a convex surface directed onto the image side; and a seventh lens L.sub.7 having a negative meniscus form with a convex surface directed onto the image side. The zoom lens further satisfies the following conditional expressions:0<(r.sub.3 +r.sub.4)/(r.sub.3 -r.sub.4)<3.5, 0.5<(r.sub.11 +r.sub.12)/(r.

Abstract: A zoom lens comprising, from front to rear, a first lens unit of positive refractive power and a second lens unit of negative refractive power, zooming being performed by varying a separation between the first lens unit and the second lens unit, wherein the first lens unit has at least two positive lenses and at least two negative lenses, and wherein the distance for the telephoto end from the first lens surface to the last lens surface, the diagonal length of the effective area of an image frame, the shortest and longest focal lengths of the entire system are appropriately determined.

Abstract: A zoom lens system is provided having a relatively small F-number, which remains nearly constant as the zoom lens system is moved from its wide-angle end to its telephoto end, and which provides an excellent imaging quality. The zoom lens system includes at least a first lens group G.sub.1 having a positive refractive power, and a second lens group G.sub.2 having a negative refractive power. The second lens group G.sub.2 moves uniformly toward the image while the first lens group G.sub.1 remains stationary. When the zoom lens system is moved from the wide-angle end to the telephoto end. The F-number is equal to or less than 2.1 over the entire zoom range.

Abstract: A zoom lens comprising, from the object end, a positive power first lens having a convex image side surface and a negative power second lens having a curvature on a concave object side surface larger than on an image side surface, the first and second lenses being movable relative to each other to vary the focal length of the zoom lens, the zoom lens satisfying the following relations:0.05<d.sub.1 /f.sub.w <0.20-0.25<R.sub.2 /f.sub.w <-0.15-0.65<R.sub.3 /f.sub.w <-0.35where d.sub.1 is the axial distance between the surfaces of the first lens;f.sub.w is the focal length at the wide angle end of the whole zoom lens;R.sub.2 is the radius of curvature of the image side surface of the first lens; andR.sub.3 is the radius of curvature of the object side surface of the second lens.

Abstract: In a compact two-group zoom lens composed of a positive front group (G.sub.1) and a negative rear group (G.sub.2), the rear group (G.sub.2) is constituted by negative, positive, and negative lenses, thereby improving productivity while attaining a high magnification of about 3.times.. The zoom lens is constituted by the front group (G.sub.1) comprising four sheets of lenses (L.sub.1 to L.sub.4) and the rear group (G.sub.2) comprising three sheets of lenses (L.sub.5 to L.sub.7). The rear group (G.sub.2) has the fifth lens (L.sub.5) made of a biconcave plastic lens having aspheric surfaces on both sides, whose surface with a stronger curvature is directed onto the object side on the optical axis (X); the sixth lens (L.sub.6) made of a biconvex lens having a surface with a stronger curvature directed onto the object side; and the seventh lens (L.sub.7) made of a negative meniscus lens having a concave surface directed onto the object side.

Abstract: A soft focus lens which is designed as a retrofocus type lens, comprises a front lens group having a negative power, a rear lens group having positive power, and a diaphragm located within the rear lens group. The front and rear lens groups are arranged in this order from an object side. In particular, the soft focus lens satisfies the following conditions;SAU/f<-0.10 (1)f/fF<-0.5 (2)whereSAU is spherical aberration at full open aperture, f is focal length of the whole lens system, and fF is focal length of the front lens group.

Abstract: A zoom lens system is composed of two lens units. The first lens unit is arranged at an object-side end and the second lens unit is arranged at an image-side end. The first lens unit has one lens element of a positive refractive power. The second lens unit has two lens elements. One is an aspherical plastic lens of non-refractive power. The other is a lens having a negative refractive power. During zooming from a wide angle end to a telephoto end, the distance between the first and second lens units is decreased.

Abstract: A zoom lens system composed, in order from the object side, of a first positive lens unit and a second negative lens unit, and configured to change a magnification thereof by varying an airspace reserved between the first lens unit and the second lens unit. The first lens unit is composed, in order from the object side, of a first negative lens element, a second plastic lens element which has at least one aspherical surface and a remarkably weak refractive power, and a cemented lens component consisting of a third negative lens element and a fourth positive lens element.

Abstract: The invention relates to a zoom lens system which, albeit having a zoom ratio as high as about 3.4, is quite well corrected for aberrations from the wide-angle to telephoto end thereof, and comprises a very reduced number of lenses involved. The zoom lens system comprises a plurality of lens groups (G1 and G2) with spaces therebetween, wherein at least one of said spaces is varied for zooming. The lens group G2 having negative refracting power is located nearest to the image surface side of the system, and includes at least one lens having positive refracting power, which is made of a gradient index lens having a refractive index varying in a direction perpendicular to the optical axis of the system. This gradient index lens has an aspheric surface on at least one side, and at least one lens having negative refracting power is located on the image surface side with respect to that gradient index lens.

Abstract: A zoom lens system having two, positive and negative, lens units, which is designed so that the number of constituent lenses is minimized to lower the cost and reduce the size, and yet high performance is realized, and that deterioration of the performance caused when the lenses are incorporated into a lens frame is minimized, and assembling is also facilitated. The zoom lens system has a 1-st lens unit (G1) of positive power and a 2-nd lens unit (G2) of negative power and is adapted to effect zooming by varying the spacing between the 1-st and 2-nd lens units (G1 and G2). The 1-st lens unit (G1) includes a single cemented lens (L.sub.12) composed of a negative lens (L.sub.1) and a positive lens (L.sub.2). The 1-st lens unit (G1) has at least one aspherical lens surface and satisfies the condition of .nu..sub.P -.nu..sub.N >15, where .nu..sub.N is the Abbe's number of the negative lens (L.sub.1), and .nu..sub.P is the Abbe's number of the positive lens (L.sub.2).

Abstract: A small-sized zoom lens is disclosed comprising, from front to rear, a first lens unit of positive refractive power and a second lens unit of negative refractive power, zooming being performed by varying the separation between the first and second lens units, wherein the first lens unit has a negative lens and at least two positive lens, the second lens unit has a first lens and a negative second lens having a concave surface facing the object side, and the second lens unit has at least one aspheric surface, and wherein proper rules of lens design are set forth for the focal lengths f1 and f2 of the first and second lens units, the shortest focal length fw of the entire system, the refractive index N2F and Abbe number .nu.2F of the material of the first lens, and the focal lengths f2F and f2R of the first and second lenses.

Abstract: A lens system is disclosed that can be used in either a normal sharp-focus configuration or in any of several soft-focus configurations for obtaining, for example, sharply focused or soft-focus photographic images of an object. The lens system has simple construction and axially comprises, in the normal sharp-focus configuration and from the object side, a first lens group having positive refractive power, an aperture stop, and a rear lens group having negative refractive power. To obtain a sharp-focus image, light passes through both lens groups and the aperture stop. For obtaining a soft-focus image, the second lens group is retracted (i.e., displaced from the optical axis such that light from the object does not pass through the second lens group), and light passes only through the first lens group and the aperture stop.

Abstract: A small, high performance zoom optical system has a simple structure that includes a positive lens group having a positive refractive power and a negative lens group having a negative refractive power arranged on an image side of the positive lens group. The positive lens group includes, in order from an object side, a first lens component with a negative refractive power, a second lens component with a negative refractive power and a third lens component with a positive refractive power. The first lens component has a meniscus shape with a concave surface facing the object side. Zooming is performed by changing the distance between the positive lens group and the negative lens group.

Abstract: Even when the refractive index of the plastic material forming a plastic lens fluctuates due to temperature change and the like, the change in the paraxial back focus amount caused by this fluctuation is canceled by spherical aberration which is generated by an aspheric surface and yields an action in a direction opposite thereto, whereby the fluctuation in refractive index in the plastic lens due to temperature change and the like is suppressed while a demand for attaining a compact size with high performances is satisfied. The second lens (L.sub.2) in the first lens group (G.sub.1) and the fourth lens (L.sub.4) in the second lens group (G.sub.

Abstract: A zoom lens system in which the back focus variations that accompany the movement of a shift lens unit can be compensated. During image shifting, the shift lens unit can be moved in a direction substantially perpendicular to an optical axis in order to shift an image. The shift lens unit also moves a small amount along the optical axis, thereby creating a back focus variation. A focusing lens unit is provided that moves along the optical axis to compensate for the variations in the back focus created by the shift lens unit during image shifting. A variation amount of the spherical aberration for the highest marginal rays at each focal length condition, when the shift lens unit undergoes a small change in position along the optical axis, divided by the amount of movement of the shift lens unit in the perpendicular direction is less than zero and greater than negative one.

Abstract: The invention provides a compact, lightweight yet low-cost zoom lens system which has a zoom ratio of at least about 2 and is well corrected for various aberrations, and in which sufficient attention is paid to temperature compensation when plastic lenses are used. The zoom lens system comprises in order from an object side a front lens group GF including a plurality of positive lenses containing at least a plastic lens and having a positive refracting power as a whole, and a rear lens group GR composed only of a plurality of negative lenses containing at least a plastic lens, wherein zooming is carried out by varying the spacing between the front and rear lens groups, and all the lenses satisfy the following condition (1):n.sub.d <1.75 (1)where n.sub.d is the d-line indices of refraction of the lenses.

Abstract: A zoom lens includes, in the order named from an object side, a first lens group having a positive refracting power and a second lens group having a negative refracting power, in which magnification change is conducted by changing a distance between said first and second lens groups. The first lens group has, in the order named from the object side, a 1a lens component having a negative refracting power, including a 1-1 lens having a negative refracting power and a 1-2 lens made of a plastic material, at least one surface of which is an aspherical surface, and a 1b lens component having a positive refracting power. The second lens group has, in the order named from the object side, a 2-1 lens having a positive refracting power made of a plastic material, at least one surface of which is an aspherical surface, and a 2-2 lens having a negative refracting power. The zoom lens satisfies the following conditional expression,2.5<f.sub.T /f.sub.W3.0<f.sub.T /f.sub.1 <5.0where f.sub.

Abstract: A zoom lens with antivibration function is provided, in the order from the object side, with a first lens group of a positive refractive power and a second lens group of a negative refractive power, which both axially move toward the object side with a reduction in the gap therebetween in the zooming operation from the wide angle end to the telephoto end. The focusing operation from a larger object distance to a smaller object distance is achieved by an axial movement of the second lens group while the first lens group remains still, while the blur in the taken image resulting from vibration is compensated by a movement of the first lens group in a direction substantially perpendicular to the optical axis.

Abstract: A zoom lens of compact form comprises, in order from an object side to an image side, a first lens unit of positive refractive power and a second lens unit of negative refractive power. The first lens unit includes a positive first lens of meniscus form convex toward the object side, a negative second lens, a negative third lens and a positive fourth lens. The second lens unit includes a positive fifth lens and a negative sixth lens. Zooming is effected by varying a separation between the first lens unit and the second lens unit, and the following conditions are satisfied:0.5<f1/fw<0.90.01<D6/fw<0.1where f1 is a focal length of the first lens unit, fw is a focal length in a wide-angle end of the zoom lens, and D6 is an axial air separation between the third lens and the fourth lens.

Abstract: A zoom lens system includes a first lens group having a positive focal length and a second lens group having a negative focal length, arranged in this order from the object side. A zooming operation of the lens system is carried out by varying the distance between the first and second lens groups. The first lens group may include a first sub-group and a second sub-group. The first sub-group and the second sub-group may each be provided with at least one negative lens element. The zoom lens system preferably satisfies the relationships defined by (1) 3.5<f.sub.L /f.sub.1 <5.0; (2) 1.77<N.sub.1 a N ; (3) 35<.upsilon..sub.1 a N <50; (4) 1.77<N.sub.1 b N ; and (5) 35<.upsilon..sub.1 b N <50; wherein "f.sub.L " represents the focal length of the whole lens system at a telephoto extremity, "f.sub.1 " represents the focal length of the first lens group, "N.sub.1 a N " represents the refractive index of the negative lens element of the first sub-group at the d-line, ".upsilon..sub.

Abstract: A zoom lens includes a front lens group and a rear lens group, which satisfies the relationship defined by the formula 1.07<Z.sub.x /Z.sub.o, wherein "Z.sub.o " represents a zoom ratio when zooming while keeping an in-focus condition for a most distant object, "Z.sub.x " represents a zoom ratio when zooming while keeping an in-focus condition for a closest object, Z.sub.x =m.sub.L /m.sub.S, Z.sub.o =f.sub.L /f.sub.S, where "m.sub.L " represents the lateral magnification of the whole lens system at a long focal length extremity and at a short object distance, "m.sub.S " represents the lateral magnification of the whole lens system at a short focal length extremity and the short object distance, "f.sub.L " represents the focal length of the whole lens system at the long focal length extremity and at the long object distance, and "f.sub.S " represents the focal length of the whole lens system at the short focal length extremity and at the long object distance.

Abstract: A compact zoom lens system is disclosed which comprises a first lens group having an overall positive refractive power and a second lens group having an overall negative refractive power. The magnification of the compact zoom lens system can be varied by varying the distance between the first lens group and the second lens group in accordance with the following condition:0.59<f.sub.I /f.sub.w <0.67where f.sub.w represents the focal length of the entire lens system, and f.sub.I represents the focal length of the first lens group.

Abstract: A compact lens system is disclosed which includes a first lens group and a second lens group. The first lens group, which has an overall positive refractive power, includes a first meniscus lens, convex toward an object, and having a positive refractive power. Also included is a second biconcave lens having a negative refractive power, and a third biconvex lens which is connected to the second lens and which has a positive refractive power. The first lens group further includes a fourth biconvex lens which has a positive refractive power. The second lens group has an overall negative refractive power, and includes: a fifth concave lens having a positive refractive power; a sixth concave lens having a negative refractive power; and a seventh lens having a negative refractive power. The magnification of the system can be changed by varying a distance between the first and the second lens group in accordance with the following condition:1.1<(f.sub.bT -f.sub.bW)/(L.sub.T -L.sub.W)<1.24where L.sub.

Abstract: A stereomicroscope comprising an objective lens system and eyepiece lens systems, the objective lens system comprising at least two lens units, permitting a working distance thereof by varying at least one airspace and having a concave surface at a location farthest from an object to be observed so as to minimize lowering of the magnification of the stereomicroscope and stereoscopic impressions of images observed through the stereomicroscope.

Abstract: To attain a compact wide-angle 2-unit zoom lens having a variable magnification range of 2.6 to 2.9 or thereabout which is well corrected for high optical performance throughout the entire variable magnification range with the total length shortened, the zoom lens comprises, in order from the object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, the separation between both the first and second lens units being varied to vary magnification, wherein an aspheric surface layer is formed on a lens surface of the object side among the lenses made of glass in the second lens unit by coating that lens surface with transparent resin and then setting the transparent resin.

Abstract: A zoom lens system includes a positive first lens group and a negative second lens group in this order from an object side. A distance between the first and second lens groups is varied during a zooming operation. The first lens group consists of a negative first sub-group and a positive second sub-group, in this order from an object side. The negative first sub-group consisting of a negative first lens element, having a concave surface facing toward the object side, and a negative second lens element, having a concave surface that faces toward an image side, in this order from the object side. The negative first sub-group being provided with at least one aspherical surface. The zoom lens system satisfies the following relationships:SF1<-34<SF2-0.4<r.sub.1-1 /f.sub.L <-0.150.15<r.sub.2-2 /f.sub.L <0.32wherein SF1 represents a shaping factor of the negative first lens element (=(r.sub.1-1 +r.sub.1-2)/(r.sub.1-1 -r.sub.

Abstract: A two-unit zoom lens system having a front lens unit of positive refractive power, and a rear lens unit of negative refractive power. The zoom lens system has a reduced number of constituent lens elements, and yet provides a zoom ratio of nearly 3 and favorable performance at reduced cost. The zoom lens system has a front lens unit (G.sub.F) of positive refractive power, and a rear lens unit (G.sub.R) of negative refractive power. Zooming is effected by varying the spacing between the two lens units. The front lens unit has a first lens component (G.sub.F1) of negative refractive power, and a second lens component (G.sub.F2) of positive refractive power. The first lens component includes no positive lens element, but has at least one aspherical surface. The second lens component includes a negative lens element and a positive lens element, which are disposed in the mentioned order.

Abstract: The invention provides a photographic lens which uses a low-hygroscopicity resin lens component as a constitutional component, is made compact without incurring some expense, and enables the optical properties to be kept stable to an atmospheric humidity change. The photographic lens is of the single-focus or varifocallength type that comprises a plurality of lens components among which at least one or more lens components are resin lens components, wherein at least one of the resin lens components is formed of a low-hygroscopicity resin. For instance, the invention is applicable to a single-focus lens comprising four lens components, i.e., a positive meniscus lens component convex on the object side, a double-concave lens component, a double-convex lens component and a negative meniscus lens component convex on the image surface side.

Abstract: The invention provides a two-unit zoom lens system comprising a front unit G.sub.F of positive refracting power and a rear unit G.sub.R of negative positive power which achieves a zoom ratio as high as about 3 with the use of a reduced number of lenses, and in which the spacing between both units is varied for zooming, said front unit including on the side proximate to the object a first lens component G.sub.F1 comprising a lens of plastic material having weak power, said first lens component including at least one aspheric surface, said rear unit including at least one positive lens and at least one negative lens, and said zoom lens system conforming to 0.2>.vertline.f.sub.W /f.sub.F1 .vertline. and 1.65<N.sub.RN where f.sub.W is the focal length of the overall system at the wide-angle end, f.sub.F1 is the focal length of said first lens component, and N.sub.RN is the refractive index of the negative lens of said rear unit.

Abstract: A lens system has a front unit having a positive refractive power and a rear unit having a negative refractive power, in order from the object side, and performs a refractive power varying (zooming) operation by changing an air gap between the two units. The front unit is composed of three lens components of negative, negative, and positive refractive powers.

Abstract: A zoom lens system which includes a positive first lens group and a negative second lens group, arranged in this order from an object side so that a distance between the first and second lens groups is changed to alter the focal length. The first lens group includes a first negative sub-lens group, and a first positive sub-lens group. The first negative sub-lens group includes a first negative lens made of glass, and a second negative lens made of plastic. The first positive sub-lens group includes a positive third lens made of glass. The negative second lens group includes a positive fourth lens made of plastic, and a negative fifth lens made of glass lens, in this order from the object side. The zoom lens system satisfies the following relationships:SF1=(r.sub.1-1 +r.sub.1-2)/(r.sub.1-1 -r.sub.1-2).ltoreq.0;andSF2=(r.sub.2-1 +r.sub.2-2)/(r.sub.2-1 -r.sub.2-2)>0where SF1 designates the shaping factor of the first negative lens, SF2 the shaping factor of the second negative lens, and r.sub.

Abstract: A compact yet high-performance zoom lens system which is well corrected in terms of aberrations, includes reduced number of lens elements and has a reduced total lens thickness. The system has a first lens group G1 including, in order from the object side, a lens having a meniscus shape convex on the object side and negative refracting power (first lens), a lens of weak refracting power (second lens) and a lens having positive refracting power together with at least one aspheric surface (third lens). The first lens group has a positive refracting power in its entirety. The system further has a second lens group G2, the focal length of the overall system being variable by varying an axial separation between the first and second lens groups G1 and G2, and conforms to the following condition: (1) relation to the refracting power range of the lens of weak refracting power and the following condition (2) relating to the axial position of the lens of weak refracting power:-0.35<f.sub.W /f.sub.LW <0.9 (1)0.

Abstract: A two lens unit zoom lens of plus, minus configuration where the rear negative group provides the primary variator function and the positive first lens unit consists of a negative sub-unit and a positive sub-unit and where the sub-units may move differentially during zooming.

Abstract: A zoom lens system for a compact camera, having a zoom ratio of approximately 2 or 3 and a smaller overall lens length at the telephoto end than the focal distance at the telephoto end, and which optically experiences only a small focus shift due to environmental changes such as temperature or humidity. The zoom lens system includes a positive lens group and a negative lens group. A positive plastic lens element is disposed in either the positive lens group or the negative lens group. The magnification of the system is adjusted by varying .?.the.!. .Iadd.a .Iaddend.distance between the positive and negative lens groups. The zoom lens system satisfies the following conditions:0.9<f.sub.t /f.sub.p <1.6 (1)0.6<m.sub.p '-m.sub.p <1.2 (2).?.2.9<.!. .Iadd.3.13.ltoreq..Iaddend.m.sub.MAX <4.0 (3)where f.sub.t is the focal length of the overall system at the telephoto end, f.sub.p is the focal length of the positive plastic lens element, m.sub.