Abstract: A zoom lens includes a positive first lens group fixed during zooming, a negative second lens moved to the image side upon zooming from the wide angle end to the telephoto end, a negative third lens group for image plane correction during zooming, and a positive fourth lens group fixed during zooming. The first lens group is composed of a negative first lens group front group, a positive first lens group middle group, and a positive first lens group rear group, disposed in order from the object side. The first lens group front group is composed of two negative lenses and one positive lens, disposed in order from the object side. Focusing is performed by moving only the first lens group middle group in an optical axis direction. The zoom lens satisfies a predetermined conditional expression.

Abstract: An optical lens system for taking image comprises, in order from the object side to the image side: a first lens element with positive refractive power having a convex object-side surface; a second lens element with negative refractive power having a concave image-side surface and an object-side surface cemented to an image-side surface of the first lens element; a third lens element with negative refractive power; a fourth lens element with positive refractive power having a concave image-side surface and at least one inflection point; and an aperture stop located between an object to be photographed and the third lens element. In the optical lens system for taking image, the number of the lens elements with refractive power being limited to four. A focal length of the optical lens system for taking image is f, a focal length of the first lens element is f1, they satisfy the relation: 0.8<f/f1<2.1.

Abstract: It is preferable that an image forming optical system includes in order from an 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 negative refractive power, and a subsequent lens group having a positive refractive power as a whole, and that the third lens group includes only a cemented lens having a negative refractive power, which includes a positive lens and a negative lens in order from the object side. Moreover, it is preferable that a cemented surface of the cemented lens in the third lens group has a shape which is convex toward an image side.

Abstract: An optical image lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element and a fourth lens element. The first lens element with positive refractive power has a convex object-side surface. The second lens element has refractive power. The third lens element with refractive power is made of plastic material, wherein an object-side surface and an image-side surface of the third lens element are aspheric. The fourth lens element with negative refractive power is made of plastic material, and has a concave image-side surface, wherein an object-side surface and the image-side surface of the fourth lens element are aspheric, and the fourth lens element has at least one inflection point formed on at least one of the object-side surface and the image-side surface thereof.

Abstract: This invention provides an optical imaging lens system in order from an object side to an image side including: a first lens element with positive refractive power having a convex object-side surface and a concave image-side surface, a second lens element with negative refractive power having a convex object-side surface and a concave image-side surface, a third lens element with positive refractive power, and a fourth lens element having a concave image-side surface, and at least one of the object-side and image-side surfaces thereof being aspheric; wherein the optical imaging lens system further comprises an aperture stop and an electronic sensor on which an object is imaged, and the aperture stop is positioned between an object and the first lens element; wherein there are four lens elements with refractive power. By such arrangement, total track length and photosensitivity of the optical imaging lens system can be effectively reduced while retaining high image quality.

Abstract: An optical image lens assembly includes, in order from an object side to an image side, a first lens element with positive refractive power and having a convex object-side surface, a second lens element with negative refractive power, a third lens element with negative refractive power and having a convex object-side surface and a concave image-side surface, and a fourth lens element with refractive power and having a concave image-side surface.

Abstract: A zoom lens comprises first and fourth units which don't move for zooming, and second and third units moved during zooming. The first unit includes a front side partial unit which don't move for focusing, a movable partial unit moved for focusing, and a rear side partial unit which don't move for focusing, the rear side partial unit includes positive lenses and one or more negative lenses, and the following conditions are satisfied: ?1.2×10?3<(?pa??n)/(?pa??n), and ?n<30, where ?n is the smallest Abbe number of the material of the negative lenses, ?n is the partial dispersion ratio of the material of the negative lens of the smallest Abbe number, ?pa is the average of the Abbe numbers ? of the materials of positive lenses, and ?pa is the average of the partial dispersion ratio ? of the materials of the positive lenses.

Abstract: A lens unit including a first lens, a second lens, a third lens, and a fourth lens arranged in order from an object side toward an image side. The first lens is laminated with the second lens. An aperture stop is held between the first lens and the second lens.

Abstract: A zoom lens comprises, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit, and a fourth lens unit having a positive refractive power. The fourth lens unit includes a forty-first lens unit having a negative refractive power and arranged at the object side with reference to the longest air gap and a forty-second lens unit having a positive refractive power and arranged at the image side with reference to the air gap. The forty-first lens unit includes a negative 411st lens, and the forty-second lens unit includes a positive 421st lens. Abbe numbers and partial dispersion ratios of materials of the 411st lens and the 421st lens ?d411, ?gF411, ?d421 and ?gF421 are appropriately set.

Abstract: A lens unit including a first lens, an aperture stop, a second lens, a third lens, and a fourth lens arranged in order from an object side to an image side. The first lens is a meniscus lens having positive power. The second lens is a meniscus lens including a convex object side surface and having negative power. The third lens is a meniscus lens including a convex image side surface and having negative power. The fourth lens is aspherical, includes an image side surface and an object side surface, and has at least one inflection point on each of the image side surface and object side surface. The image side surface has a concave surface facing toward the image side.

Abstract: This invention provides an imaging lens assembly including, in order from an object side to an image side: a first lens with positive refractive power having a convex object-side surface; a second lens with negative refractive power having a convex image-side surface; a third lens having a concave object-side surface and a convex image-side surface, at least one of both surfaces thereof being aspheric; a fourth lens having a concave image-side surface, at least one of both surfaces thereof having at least one inflection point; and an aperture stop disposed between an imaged object and the second lens; the on-axis spacing between the first lens and second lens is T12, the focal length of the imaging lens assembly is f, the Abbe number of the first lens and third lens is, V1 and V3, respectively, they satisfy the relations: 0.5<(T12/f)*100<20, 23<V1?V3.

Abstract: Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system of the present invention includes, in order from object side to image side, a first lens unit G1 having positive optical power, a second lens unit G2 having negative optical power, a third lens unit G3 having negative optical power, and a fourth lens unit G4 having positive optical power. An aperture diaphragm A is arranged on the object side adjacent to the fourth lens unit G4. Further, the fourth lens unit G4 includes, in order from object side to image side, a lens element L8 having positive optical power, a lens element L9 having positive optical power, and a lens element L10 having negative optical power.

Abstract: An imaging apparatus includes a first lens has a positive refractive power, a second lens has a positive refractive power, a third lens has a negative refractive power, a fourth lens has a negative refractive power, an image sensor and a driving device. The first lens, the second lens, the third lens, the fourth lens and the image sensor are arranged in the order written along an optical axis of the imaging apparatus from the object side to the image side thereof. The driving device is connected to the second lens and configured for driving the second lens to move toward the object side to perform a zoom-in function of the imaging apparatus.

Abstract: A zoom lens system includes four lens units each having positive, negative, negative and positive refractive powers in the stated order from an object side to an image side. A first lens unit includes a variable apex angle prism on the image side of at least one lens element. In this zoom lens system, a focal length of the first lens unit and imaging magnifications of a second lens unit and a fourth lens unit are set appropriately so as to suppress occurrence of decentering aberration accompanying a variation of a prism apex angle.

Abstract: A zoom lens system includes, in order from the object side to the image side, four lens units having positive, negative, negative and positive refractive powers. A first lens unit includes, in order from the object side to the image side: a front subunit having a negative refractive power; a middle subunit that has a positive refractive power and moves during focusing; and a rear subunit having a positive refractive power. The zoom lens system further includes a variable apex angle prism disposed on the image side of the front subunit. An average Abbe number of materials of a negative lens element and a positive lens element included in the front subunit is set appropriately so as to suppress occurrence of decentering aberration accompanying a variation of a prism apex angle.

Abstract: An optical lens system for taking image has, in order from the object side to the image side: a positive first lens element with a convex object-side surface; a negative plastic second lens element with a concave object-side surface; a negative plastic third lens element with a concave object-side surface; a positive fourth lens element with a concave image-side surface; and an aperture stop located between an object to be photographed and the second lens element. The second lens element is provided with at least one aspheric surface, the third lens element is provided with at least one aspheric surface, and the fourth lens element is formed with inflection points. An on-axis distance between the first and second lens elements is T12, a focal length of the optical lens system for taking image is f, they satisfy the relation: (T12/f)*100>0.7.

Abstract: An optical lens system for taking image comprises: a first lens element with positive refractive power, an Abbe Number of the first lens element being V1, and it satisfying the relation: 50<V1<60; a second lens element with negative refractive power having a concave object-side surface and a convex image-side surface; a third lens element having a convex object-side surface and a concave image-side surface, at least one of the object-side and the image-side surfaces of the third lens element being aspheric; a fourth lens element having at least one aspheric surface; and an aperture stop being located in front of the second lens element.

Abstract: An optical lens system for taking image comprises, in order from the object side to the image side: a first lens element with positive refractive power having a convex object-side surface; a second lens element with negative refractive power having a concave image-side surface and an object-side surface cemented to an image-side surface of the first lens element; a third lens element with negative refractive power; a fourth lens element with positive refractive power having a concave image-side surface and at least one inflection point; and an aperture stop located between an object to be photographed and the third lens element. In the optical lens system for taking image, the number of the lens elements with refractive power being limited to four. A focal length of the optical lens system for taking image is f, a focal length of the first lens element is f1, they satisfy the relation: 0.8<f/f1<2.1.

Abstract: An optical lens system for taking image comprises: a first lens element with positive refractive power, an Abbe Number of the first lens element being V1, and it satisfying the relation: 50<V1<60; a second lens element with negative refractive power having a concave object-side surface and a convex image-side surface; a third lens element having a convex object-side surface and a concave image-side surface, at least one of the object-side and the image-side surfaces of the third lens element being aspheric; a fourth lens element having at least one aspheric surface; and an aperture stop being located in front of the second lens element.

Abstract: A subminiature imaging optical system including: first, second, third and fourth lenses sequentially positioned from an object side to an image side, the first lens having positive refractivity, the second lens having a concave image-side surface and having negative refractivity, the third lens having negative refractivity, and the fourth lens having positive refractivity, wherein the second lens satisfies following condition 1, and the third lens satisfies following condition 2, 20<V2<50??condition 1, 20<V3<50??condition 2, where V2 is an Abbe number of the second lens and V3 is an Abbe number of the third lens.

Abstract: There is provided a subminiature imaging optical system installed in a mobile telecommunication terminal or a PDA, or used in a surveillance camera or a digital camera. The subminiature imaging optical system including: first, second, third and fourth lenses sequentially positioned from an object side to an image side, the first lens having positive refractive power, the second lens having negative refractive power, the third lens having negative refractive power, and the fourth lens having positive refractive power, wherein each of the third and fourth lenses has at least one aspherical surface. The subminiature imaging optical system corrects chromatic aberration superbly to reduce color fringing significantly, thereby achieving high resolution and compactness as well.

Abstract: An imaging module and method of fabrication. The method comprises forming a first lens wafer with a plurality of outer negative lenses and forming a second lens wafer with a plurality of inner negative lenses The method further comprises bonding the first lens wafer and second lens wafer to create a bonded stack; forming a plurality of inner positive lenses on the second lens wafer and bonding a spacer wafer to the second lens wafer; and forming a plurality of outer positive lenses on the first lens wafer.

Abstract: A lens unit including a first lens, a second lens, a third lens, and a fourth lens arranged in order from an object side toward an image side. The first lens is laminated with the second lens. An aperture stop is held between the first lens and the second lens.

Abstract: A rear-focusing type zoom lens includes, in order from an object side, a positive first group being fixed, a negative second group moving toward an image plane along an optical axis during zooming from a wide-angle end to a telephoto end; a negative third group being fixed in an optical axis direction, and a positive fourth group moving along the optical axis direction to correct image plane variation being caused by zooming. The first group includes a first subgroup having a negative power as a whole and a second subgroup having a positive power as a whole. The first subgroup includes a negative meniscus lens having a convex surface directed toward the object side and a negative lens. The second subgroup includes a positive lens group having at least one positive lens, a negative lens, a positive lens, and another positive lens group having at least one positive lens.

Abstract: A subminiature imaging optical system including: first, second, third and fourth lenses sequentially positioned from an object side to an image side, the first lens having positive refractivity, the second lens having a concave image-side surface and having negative refractivity, the third lens having negative refractivity, and the fourth lens having positive refractivity, wherein the second lens satisfies following condition 1, and the third lens satisfies following condition 2, 20<V2<50 condition 1, 20<V3<50 condition 2, where V2 is an Abbe number of the second lens and V3 is an Abbe number of the third lens.

Abstract: At least one exemplary embodiment is directed to an optical system which includes a plurality of refractive optical elements arranged substantially symmetrically with respect to an aperture-stop. Furthermore the optical system comprises a refractive optical element being constituted by a solid material. An Abbe number ?d of the solid material and a partial dispersion ratio ?gF of the solid material can satisfy the following conditions: ?gF?(?1.665×10?7·?d3+5.213×10?5·?d2?5.656×10?3·?d+0.755)>0, ?gF?(?1.665×10?7·?d3+5.213×10?5·?d2?5.656×10?3·?d+1.011)<0.

Abstract: A lens for reading an original, comprises five lenses as a whole including two positive and two negative lenses, an aspherical surface provided on at least one surface of the five lenses, a construction of four lens groups for five lenses which include a cemented lens constructed by cementing one of the positive lenses and one of the negative lenses, an aperture stop disposed between a second and third lens groups, and the cemented lens disposed adjacent to the aperture stop.

Abstract: A lens that can be used in a digital camera includes in sequence a first lens element (20), a second lens element (30), a third lens element (40), and a fourth lens element (50). The first lens element is biconvex, and includes a first aspheric surface (22) and a second aspheric surface (24). The second lens is biconcave, and includes a third aspheric surface (32) and a fourth aspheric surface (34). The third lens element is concavo-convex, and includes a fifth aspheric surface (42) and a sixth aspheric surface (44). The fourth lens element includes a seventh aspheric surface (52) and a eighth aspheric surface (54), the seventh aspheric surface and the eighth aspheric surface being wavelike. All of the lens elements are made from plastic. The lens is light, has strong impact resistance, and provides good image quality.

Abstract: A compact, lightweight, and high-performance lens and method of using the same are provided. In one embodiment, the lens includes a crown glass having a first aspheric surface, a flint glass optically coupled to the crown glass, the first flint glass having a second aspheric surface, and an air gap between the crown glass and the flint glass.

Abstract: An original reading lens includes a four-group, five-element lens configuration including three positive lenses and two negative lenses, wherein the positive lens is constructed by a glass material of low dispersion, and the negative lens is constructed by a glass material of high dispersion, a partial dispersion ?gd is defined by ?gd=(ng?nd)/(nF?nc) by a refractive index nd of d line (587.56 nm), a refractive index nc of c line (656.27 nm), a refractive index nF of F line (486.13 nm), and a refractive index ng of g line (435.

Abstract: A zoom lens according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. During a magnification change from the wide-angle end through the telephoto end, the first lens unit and the fourth lens unit shift from the image-surface side toward the object side, a space between the first lens unit and the second lens unit increases, and spaces between individual lens units change. During a focusing from an object at the infinite distance onto an object at a near distance, the second lens unit and the third lens unit individually shift independently.

Abstract: There is disclosed a zoom lens having small variations of aberration and field angle during focusing and having a small system as a whole. The zoom lens includes a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a negative optical power, a fourth lens unit having a positive optical power, and a fifth lens unit having a positive optical power, in order from an object side to an image side. During zooming, the second lens unit and third lens unit are moved, and during focusing, the fifth lens unit is moved. The fifth lens unit consists of one negative lens element and two positive lens elements in order from the object side to the image side, and the following conditions are satisfied: 0<?5<0.35 1.85<?5p/?5n.

Abstract: A high-power, four-group zoom lens is disclosed which is formed of only four lens groups, in order from the object side, a first lens group of positive refractive power, a second lens group of negative refractive power, and third lens group of negative refractive power, and a fourth lens groups of positive refractive power. The fourth lens group includes, in order from the object side, a front lens subgroup and a rear lens subgroup. The rear lens subgroup includes, in order from the object side, a lens component of positive refractive power that includes a lens element, a pair of lens elements that may form a doublet component that includes a lens element of positive refractive power, a doublet component, and a lens component of positive refractive power. Specified conditions are satisfied to minimize lateral color and curvature of field.

Abstract: A lens for reading an image of a document includes three positive lenses, three negative lenses, a diaphragm, and at least one cemented lens that includes one of the positive lenses and one of the negative lenses cemented together. The document reading lens includes at least one aspheric surface. The lens adjacent to the diaphragm has the aspherical surface, and at least one cemented lens is arranged to be adjacent to the diaphragm.

Abstract: An imaging optical system having superior optical performance with the improved correction of chromatic aberration over a wide wavelength range extending from the visible wavelength range to the infrared wavelength range is provided. According to one aspect, an imaging optical system includes, in order from an object, a front lens group GF with a positive refractive power having at least one lens element, an aperture stop SP and a rear lens group GR with a positive refractive power having at least one lens element. The front lens group GF includes a double convex positive lens GT arranged to the most object side. At least one of the front lens group GF and the rear lens group GR includes a triple cemented lens GS being adjacent to the aperture stop SP having a negative refractive power as a whole composed of a first positive lens, a negative lens, and a second positive lens. Predetermined conditional expression is satisfied.

Abstract: A color image readout lens having four lens groups of positive, positive or negative, negative, and positive refractive power, respectively, in order from the object side. The first lens group is formed of a first lens element having a convex surface on the object side. The second lens group has a convex surface of the object side and is formed of a biconvex lens element that is cemented to a biconcave lens element. The third lens group is formed of a fourth lens element that is cemented to a fifth lens element, with the fifth lens element having positive refractive power and a convex surface on the image side. A fourth lens group is formed of a sixth lens element having a convex surface on the image side. Various conditions are satisfied in order to favorably correct the various aberrations.

Abstract: An optical system provided with a lens, a stop and a diffraction grating is characterized in that when in a state wherein the diffraction grating is absent, the value of the coefficient of chromatic aberration of magnification of the wavelength of the long wavelength side relative to the reference wavelength of light is positive, the diffraction grating is disposed more adjacent to an incidence surface side than the stop, and when in the state wherein the diffraction grating is absent, the value of the coefficient of chromatic aberration of magnification of the wavelength of the long wavelength side relative to the reference wavelength of the light is negative, the diffraction grating is disposed more adjacent to an emergence side than the stop.

Abstract: A color image readout lens having four lens groups of positive, positive or negative, negative, and positive refractive power, respectively, in order from the object side. The first lens group is formed of a first lens element having a convex surface on the object side. The second lens group has a convex surface of the object side and is formed of a biconvex lens element that is cemented to a biconcave lens element. The third lens group is formed of a fourth lens element that is cemented to a fifth lens element, with the fifth lens element having positive refractive power and a convex surface on the image side. A fourth lens group is formed of a sixth lens element having a convex surface on the image side. Various conditions are satisfied in order to favorably correct the various aberrations.

Abstract: A real image type view finder comprising an objective optical system which has positive refractive power and forms an intermediate image, an image erecting optical system which erects the intermediate image and an eyepiece optical system which leads the intermediate image to an observer's eye, in which the objective optical system comprises a first positive lens unit, a second negative lens unit, a third negative lens unit and a fourth positive lens unit, moves the second lens unit and the third lens unit for a magnification change, has a vari-focal ratio on the order of 4, and has favorable optical performance over an entire zooming region.

Abstract: In an image readout lens comprising four lens elements having positive, negative, negative, and positive refracting powers, respectively, the glass material for at least one of the second and third lenses is defined in terms of relative partial dispersion and Abbe number, so as to yield an image readout lens which favorably corrects chromatic aberration and is suitable as a color-image readout lens. Disposed successively from the object side are a first lens L1 made of a positive meniscus lens which is convex toward the object, a second lens L2 and a third lens L3 each having a surface on an image side concave toward the image and a negative refracting power, and a fourth lens L4 made of a biconvex lens, wherein a lens glass material of at least one of the second lens L2 and third lens L3 satisfies the following conditional expression (1): &thgr;g·F+0.0019&ugr;d<0.

Abstract: An original reading lens for imaging the image information on the surface of an original on the surface of a sensor, includes an original reading lens having, in succession from the original side, a meniscus-shaped positive first lens having its convex surface facing the original side, a meniscus-shaped negative second lens having its convex surface facing the original side, a stop, a meniscus-shaped negative third lens having its convex surface facing the sensor side, and a meniscus-shaped positive fourth lens having its convex surface facing the sensor side, and the surface of a diffracting optical element disposed near the stop.

Abstract: A Bravais lens includes a front, positive power lens group and a rear, negative power lens group. These lens groups, in combination, provide the Bravais lens with a negative focal length and a negative power. The front, positive power lens group includes a positive power lens element and a negative power lens element. The rear, negative power lens group includes another negative power lens element and another positive power lens element.

Abstract: A zoom lens optical system has a first-lens set having a positive refracting power, a second-lens set having a negative refracting power, a third-lens set having a negative refracting power, a fourth-lens set having a positive refracting power, and an optical path splitter means. The first through fourth-lens set and the optical path splitter means are located in this order from the side of a plane of image formation. The zoom lens optical system satisfies the conditions1.2 fw<f1<2.4 fw, and0.4 fw<f3/f2<0.8 fwwhere fw is a number equal to the minimum focal length of the whole system in millimeters, f1 is a number equal to the composite focal length of the first-lens set in millimeters, f2 represents the composite focal length of the second-lens set in millimeters, and f3 represents the composite focal length of the third-lens set in millimeters.

Abstract: Low-power objective lenses for a microscope are disclosed. The objective lenses exhibit apochromatic optical performance at a numerical aperture of at least 0.1 and have a magnification of about 2.times. or less. Each such objective lens comprises, in order from the object side, a first lens group having positive refractive power; a second lens group having negative refractive power and comprising a negative meniscus lens with a concave surface oriented toward the image side; a third lens group having negative refractive power and having at least one cemented surface; and a fourth lens group having positive refractive power and comprising a positive meniscus lens element with a convex surface oriented toward the image side, and a positive cemented lens including a negative lens element cemented to a positive lens element. The objective lenses satisfy the condition: 1.2<f.sub.1 /D.sub.1 <2.3 and other conditions, wherein f.sub.l is focal length of the first lens group and D.sub.

Abstract: In a Xenotar type image-readout lens of a four-group five-element configuration, predetermined conditional expressions are satisfied so as to attain a bright lens system, while favorably correcting chromatic aberration. In a Xenotar type lens system composed of five sheets of lenses (L.sub.1 to L.sub.5), the second lens (L.sub.2) and the third lens (L.sub.3) are cemented together, a stop (i) is disposed between the third lens (L.sub.3) and the fourth lens (L.sub.4), and the following conditional expressions are satisfied:1.78.ltoreq.N.sub.1, 47.0<.upsilon..sub.3 +.upsilon..sub.4 <57.0, 1.4<f.sub.123 /f<2.0, 22<.upsilon..sub.2 -.upsilon..sub.3,1.37<.vertline.f.sub.2 /f.sub.3 .vertline.<1.64, 1.24<R.sub.42 /R.sub.41 <1.37, 33<.upsilon..sub.5 .times.(N.sub.

Abstract: A zoom lens system having a high zoom ratio and a high aperture ratio includes a first lens group having a positive power, a second lens group having a negative power, a third lens group having a negative power, and a fourth lens group having a positive power. The second lens group has a magnification varying function and is moved during a zooming operation. The third lens group has a focus compensating function and is moved during the zooming operation. The fourth lens group has an image forming function and is not moved during the zooming operation.

Abstract: A zoom lens system comprising, in order from the object side, a first lens unit which has a positive refractive power and is to be kept stationary for zooming the lens system, a second lens unit which has a negative refractive power and is movable for zooming said lens system, and a third lens unit which has a positive refractive power and is to be kept stationary for zooming the lens system: the second lens unit consisting of a front subunit having a negative refractive power and a rear subunit having a negative refractive power. The zoom lens system is configured so as to corect a deviation of an image location by varying, during zooming, an airspace reserved between the front subinit and the rear subunit.

Abstract: A zoom lens system comprises in the following order from the object side: a first lens group of a positive refracting power; a second lens group of a negative refracting power; a third lens group; and a fourth lens group of a positive refracting power, wherein, when changing a focal length of the zoom lens system from a wide-angle end to a telephoto end, the second lens group is shifted in one direction along an optical axis of the zoom lens from the object side toward the image side, the third lens group is shifted so as to reciprocate along the optical axis, and the first lens group has a gradient index lens whose refractive index varies along the direction of the optical axis and which satisfies the following condition:-10.6<(.nu.2-.nu.1)/[(n2-n1).multidot.100]<-0.9whereinn1: a refractive index at an object-side vertex of the gradient index lens,n2: a refractive index at an image-side vertex of the gradient index lens,.nu.1: Abbe number at the object-side vertex of the gradient index lens,.nu.

Abstract: A copy lens comprising four lens elements arranged symmetrically with an aperture, namely, in order from the object end to the image end, a first biconvex element and a biconcave element, which are positioned on one side of the aperture, a third biconcave element identical with the second biconcave element and a fourth biconvex element identical with the first biconvex element, which are positioned on another side of the aperture.

Abstract: An imagery lens system for image reading consists of first to fourth lens elements which are arranged in this order from the object side. The first and fourth lens elements respectively are double-convex lenses, and the second and third lens elements respectively are double-concave lenses. The following formulae are satisfied.0.35<f1/f<0.51--(1)0.34<f4/f<0.45--(2)0.11<d7/f<0.16--(3)0.29<d/f<0.41--(4)wherein f represents the synthetic focal length of the overall lens system, f1 represents the focal length of the first lens element, f4 represents the focal length of the fourth lens element, d represents the axial surface separation between the object side face of the first lens element and the image side face of the fourth lens element and d7 represents the central thicknesses of the fourth lens element.