Abstract: An imaging device may generate a zoom image corresponding to a plurality of magnifications by adjusting an effective focal length through a multi-layer optical system including an active imaging array having an active imaging lens.

Abstract: A six-piece optical lens for capturing image and a six-piece optical module for capturing image are disclosed. In order from an object side to an image side, the optical lens along the optical axis includes a first lens with refractive power; a second lens with refractive power; a third lens with refractive power; a fourth lens with refractive power; a fifth lens with refractive power; a sixth lens with refractive power; and at least one of the image-side surface and object-side surface of each of the six lens elements is aspheric. The optical lens can increase aperture value and improve the imagining quality for use in compact cameras.

Abstract: A six-piece optical lens for capturing image and a six-piece optical module for capturing image are disclosed. In order from an object side to an image side, the optical lens along the optical axis comprises a first lens with refractive power; a second lens with refractive power; a third lens with refractive power; a fourth lens with refractive power; a fifth lens with refractive power; a sixth lens with refractive power; and at least one of the image-side surface and object-side surface of each of the six lens elements is aspheric. The optical lens can increase aperture value and improve the imagining quality for use in compact cameras.

Abstract: A projection system includes a first optical system, a second optical system including a first optical element and a second optical element and disposed on the enlargement side of the first optical system, and a placement mechanism configured to selectively place one of the first and second optical elements on a first optical axis of the first optical system. The first optical element has a first light incident surface, a first reflection surface disposed on the enlargement side of the first light incident surface, and a first light exiting surface disposed on the enlargement side of the first reflection surface. The second optical element has a second light incident surface, a second reflection surface disposed on the enlargement side of the second light incident surface, and a second light exiting surface disposed on the enlargement side of the second reflection surface.

Abstract: A lens module for capturing an object light-beam from an object-side is provided. The lens module includes a first lens group, a second lens group, a third lens group, a fourth lens group and a fifth lens group sequentially-arranged from the object-side to an image-side. The five lens groups respectively have at least one lens with positive refractive-power and at least one lens with negative refractive-power. The first, third and fifth lens groups are fixed groups, while the second and fourth lens groups are movable groups. An image apparatus including the lens module is also provided.

Abstract: An optical zoom device for setting an imaging scale of an imaging device, which is configured for imaging an object on an image plane of an image recording device using a microscope objective, comprising an optical element arrangement is disclosed. The optical element arrangement includes an object-side zoom entrance for optical connection to an objective exit, in particular a collimated objective exit, of the microscope objective and includes an image-side zoom exit for optical connection to an image recording entrance of the image recording device.

Abstract: A zoom lens includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a rear unit including a plurality of lens units. A distance between adjacent lens units changes during zooming. An aperture stop is arranged on an image side of the first lens unit. An image stabilizing unit Ls comprising at least part of the second lens unit moves in a direction perpendicular to an optical axis during blurring correction. The predetermined conditional expressions are satisfied.

Abstract: A zoom lens includes, in order from object side to image side, a first lens unit having positive refractive power; a second lens unit having negative refractive power; a third lens unit having positive refractive power; and a rear lens group including one or more lens units. During zooming, three or more lens units move to change an interval between adjacent lens units. The third lens unit includes, in order from object side to image side, a first lens subunit having positive refractive power, a second lens subunit having negative refractive power, and a third lens subunit having positive refractive power. The second lens subunit moves in a direction having a component perpendicular to the optical axis regarding image blurring correction, a focal length of the zoom lens at the telephoto end and a focal length of the third lens unit are set to satisfy specific mathematical conditions.

Abstract: An optical system includes, in order from an object side to an image side, a first lens unit of a positive refractive power, an aperture diaphragm, and a second lens unit of a positive refractive power. The first lens unit includes, in order from the object side to the image side, a cemented lens Lp1 made by joining a first lens of a positive refractive power and a second lens of a negative refractive power with each other, and a third lens of a positive refractive power which has a meniscus shape. The predetermined conditions are satisfied.

Abstract: A zoom lens assembly may enlarge/reduce an image without shifting a position of a lens set. A housing, a zoom lens unit and a drive unit may be provided. The zoom lens unit may include a plurality of lenses stationarily arranged within the housing by being spaced apart in prescribed distance from each other along an optic axis. The plurality of the lenses respectively have variable refractive indexes without a position shift. The drive unit may pressurize a prescribed one of the lenses to vary the refractive index of the prescribed lens. The controller may control the drive unit to change a focal distance of the zoom lens unit to enlarge or reduce an image.

Abstract: A zoom lens system used in a spectrum region including visible light has movable lens groups moved for zooming, and has, in a movable lens group, a negative lens element made of a material fulfilling the conditional formulae Vd<55 and 0.0018×Vd+P<0.65 and, in a movable lens group, a positive lens element made of a material fulfilling the conditional formulae 60<Vd, 0.645<0.0018×Vd+P, and 9×10?6<dN/dT, where Vd is the Abbe number for a d-line; P=(Ng?NF)/(NF?NC); Ng, NF, and NC are the refractive indices for the g-, F-, and C-lines respectively; and dN/dT is the variation rate in refractive index accompanying variation in room temperature. The negative and positive lens elements move in the same direction during zooming.

Abstract: A tunable, achromatizing optical system for use with a broadband imaging modality system for imaging objects having a range of longitudinal chromatic aberration (LCA) values. The optical system includes an achromatizing component and a parfocal component, for example, a zoom system. A method for tuning the wavefront curvature of different chromatic components of objects having a range of longitudinal chromatic aberration (LCA) values when imaged by a broadband imaging modality system includes the steps of providing a broadband imaging modality system having an entrance pupil, for imaging an object having longitudinal chromatic aberration; providing a tunable, achromatizing optical system; and varying the focal length of the parfocal component while maintaining a conjugate relationship between the achromatizing component and the entrance pupil of the broadband imaging modality system.

Abstract: To provide an image forming optical system that can achieve good correction of chromatic aberration, which is seriously needed particularly when the zoom ratio is high, while achieving slimness and a high zoom ratio and to provide an electronic image pickup apparatus equipped with such an image forming optical system, an image forming optical system has a lens group A including a lens component made up of a positive lens LA and a negative lens LB cemented together and having a negative refracting power as a whole. The lens group A is arranged between a lens group I closest to the object side and an aperture stop. The distance between the lens group I and the lens group A changes for zooming. The lens component has an aspheric cemented surface, and a certain condition concerning the shape of the aspheric surface is satisfied.

Abstract: A zoom lens includes a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, the first, second, third, and fourth lens groups being arranged in order from an object side, and satisfies conditional expression (1) and conditional expression (2) below, (1) 0.95<|fw12|/fw<1.2 and (2) 140<f1/?t234<150, where, fw12 denotes a synthetic focal length of the first lens group and the second lens group at a wide-angle end, fw denotes a focal length of a whole lens system at the wide-angle end, f1 denotes the focal length of the first lens group, and ?t234 denotes the synthetic magnification of the second lens group, the third lens group, and the fourth lens group at a telephoto end.

Abstract: A condensing optical system having a condensed light spot with a small size and a large focal depth without causing a problem of a decrease in intensity of the condensed light spot or discontinuity of an intensity distribution in front and rear areas of a focal position is provided. The condensing optical system that condenses a laser beam generated by a laser source at a predetermined focal length is designed to satisfy Expressions (a) to (d), thereby producing 3rd and 5th spherical aberrations: |Z8|?0.1? or |Z15|?0.05?,??(a) Z8/Z15?3 or Z8/Z15<1,??(b) |Z8|<1.4?, and??(c) |Z15|<0.5?,??(d) where ? is a wavelength, Z8 is an 8th coefficient of coefficients of the Zernike fringe polynomial of wavefront aberration corresponding to a 3rd order spherical aberration, and Z15 is a 15th coefficient of the coefficients of the Zernike fringe polynomial of wavefront aberration corresponding to a 5th spherical aberration.

Abstract: This invention provides an imaging lens system including, in order from an object side to an image side: a first lens group with negative refractive power comprising a single first lens element with negative refractive power; a second lens group with positive refractive power comprising, in order from the object side to the image side: a second lens element with positive refractive power; a third lens element with negative refractive power; an aperture stop; and a fourth lens element with negative refractive power; and a third lens group with positive refractive power comprising a single fifth lens element with positive refractive power; wherein by moving the first lens group and the second lens group along the optical axis while keeping the third lens group stationary, the zooming operation is performed such that the system switches between a wide-angle mode and a telephoto mode.

Abstract: A linear motion control device for use in a linear control system is presented. The linear motion control device includes a coil driver to drive a coil that, when driven, effects a linear movement by a motion device having a magnet. The linear motion control device also includes a magnetic field sensor to detect a magnetic field associated with the linear movement and an interface to connect an output of the magnetic field sensor and an input of the coil driver to an external controller. The interface includes a feedback loop to relate the magnetic field sensor output signal to the coil driver input.

Abstract: A compact zoom lens system includes, in order from an object side to an image side along an optical axis thereof, a first lens group having positive refractive power, a second lens group having positive refractive power and a third lens group also having positive refractive power. The first lens group is stationary and includes a reflecting element for bending the optical path. The second and third lens groups are movable along the optical axis, and each of the first, second and third lens groups has at least one aspheric lens surface. When zooming from a wide-angle end to a telephoto end, the second lens group moves toward the object side and the third lens group moves toward the image side, so as to reduce the spacing between the first and second lens groups and increase the spacing between the second and third lens groups. By this specific optical configuration, the compact zoom lens system has the advantages of small size, simple structure, low cost, good reliability and better image quality.

Abstract: A zoom lens comprises, in order from its object side, a front lens group having negative refracting power at a wide-angle end and a rear lens group having positive refracting power at the wide-angle end. The front lens group comprises, in order from the object side, a first lens group of positive refracting power and a second lens group of negative refracting power, and the rear lens group comprises, in order from the object side, a third lens group of positive refracting power and a fourth lens group of positive refracting power. There is an aperture stop interposed between the lens surface located in, and nearest to the object side of, the second lens group and the lens surface located in, and nearest to the image size of, the third lens group.

Abstract: An optical system includes a first negative lens element disposed nearest a front side and a first positive lens element whose front surface resides within a distance 0.4 L from the surface nearest the front side toward a rear side of the optical system having a total lens length L. By appropriately determining the materials for the two lens elements, the optical system realizes a wide angle of view while correcting lateral chromatic aberration well.

Abstract: Disclosed is a phase retardation film including two outer layers facing each other, and an inner layer interposed between the outer layers, each of the outer layers are formed of a non-styrene polymeric material and the inner layer being formed of a polymeric material with a negative intrinsic birefringence, wherein the phase retardation film has a negative intrinsic birefringence and a Haze from 0% to 1%. A liquid crystal display device including the phase retardation film is also disclosed.

Abstract: A display element having a plurality of pixel portions arranged two-dimensionally with a predetermined pixel pitch and a microlens array including a plurality of microlenses arranged two-dimensionally corresponding to the plurality of pixel portions on an incident side or an emission side of light with respect to the pixel portions, wherein, in the microlens array, each microlens has a lens surface of a hyperboloid of revolution, and a lens pitch of the plurality of microlenses is set to a pitch smaller than the lens pitch able to substantially equivalently maintain a converging efficiency of a lens of the hyperboloid of revolution and a lens of an ellipsoid of revolution with respect to the incident light and able to maintain a converging efficiency higher than the converging efficiency of the lens of the ellipsoid of revolution or wherein, in the microlens array, each microlens has a lens surface of a hyperboloid of revolution, and a lens pitch is 20 ?m or less; a display device; and a microlens array.

Abstract: A zoom lens includes, in order from the object side, the first lens unit consisting of one negative lens component in which a plurality of lens components are cemented to one another and the second lens unit including one negative lens component and having positive refracting power as a whole. In this case, the zoom lens satisfies the following condition: 0.15<t1/fw<0.6 where t1 is the thickness, measured along the optical axis, of the first lens unit and fw is the focal length of the entire system at the wide-angle position of the zoom lens.

Abstract: A diffraction grating device (100) has both reflecting (108) and transmitting (106) gratings inter leaved to allow both transmission diffraction patterns and reflection diffraction patterns to be formed by means of the same device (102). This makes it possible, for example, to produce a diffraction pattern of one older with a beam (134) directed to be diffracted by the reflecting diffraction grating or with a beam (132) directed to be diffracted by the transmitting diffraction grating when either beam is incident alone. It also makes it possible to generate a diffraction pattern of a different order when both beams are incident simultaneously, which reduces effective order of the grating.

Abstract: An active optical zoom system changes the magnification (or effective focal length) of an optical imaging system by utilizing two or more active optics in a conventional optical system. The system can create relatively large changes in system magnification with very small changes in the focal lengths of individual active elements by leveraging the optical power of the conventional optical elements (e.g., passive lenses and mirrors) surrounding the active optics. The active optics serve primarily as variable focal-length lenses or mirrors, although adding other aberrations enables increased utility. The active optics can either be LC SLMs, used in a transmissive optical zoom system, or DMs, used in a reflective optical zoom system. By appropriately designing the optical system, the variable focal-length lenses or mirrors can provide the flexibility necessary to change the overall system focal length (i.e.

Abstract: In a nearer order from its object, a first lens group which has a negative refractive power, a brightness diaphragm, and a second lens group which has a positive refractive power, and a moving lens group which moves on an optical axis, conditions such as 2?DL/fW?6, and ?2?DVH/fW?0.37 are satisfied under condition that DL (mm) indicates an air-converged length from an end surface near an image in the first lens group to an end surface nearer to an object in the moving lens group, fW (mm) indicates a focal length in an entire system in a wide angle end, DVH (mm) indicates a distance from the end surface near the object in the moving lens group to a front principal point. By doing this, it is possible to provide an objective optical system which can obtain a high magnification while securing a sufficient distance between the diaphragm which is disposed behind the optical axis direction converting element such as a prism to the moving lens group.

Abstract: A zoom optical system includes only one optical-element group moved in a magnification change and at least one deformable mirror having a compensating function for compensating for a shift of an image surface caused by the magnification change and a focusing function. According to this configuration of the zoom optical system, it is possible to attain a zoom optical system and an imaging apparatus using the zoom optical system that have as small a number of movable lenses as possible, are very small in size, and work with an extremely low power consumption and low operation noise.

Abstract: The invention provides a zoom lens device that can include lens groups. A third lens group (compensator lens group) can be disposed between two lens groups (a second and a fourth lens groups) forming a variator lens group. The two lens groups (the second and fourth lens groups) forming the variator lens group can be retained by a common variator-lens frame and moved together. Accordingly, a zoom lens device, an optical apparatus, and a projector can be provided in which, even when a plurality of lens groups are assembled, degradation of optical characteristics due to decentering between the lens groups can be prevented.

Abstract: A coma compensating element has two refraction surfaces. The refraction surfaces provide, as a whole, no aberration with respect to rays perpendicularly incident thereon, while the refraction surfaces provide coma with respect to rays obliquely incident thereon.

Abstract: An optical system includes a diffractive optical element in which a phase given to incident light from an optical axis toward the peripheral part in the radial direction is not reversed in an effective area and an absolute value of optical power on the optical axis is made minimum. In the optical system, chromatic aberration of magnification of a high order is satisfactorily corrected and flare caused by additional diffraction light (unnecessary diffraction light) is suppressed to as minimum as possible while maintaining a high imaging performance up to peripheral part of a field angle.

Abstract: A zoom lens includes a first lens unit with a positive refractive power, a second lens unit with a negative refractive power, a third lens unit with a positive refractive power, and a fourth lens unit with a positive refractive power, which are arranged in this order from an object side. At least the first, third and fourth lens units are moved along an optical axis to vary spatial distances of the lens units to thereby change the magnification of the zoom lens. The third lens unit includes a first lens subunit with a positive refractive power, and a second lens subunit with a negative refractive power, and the second lens subunit is moved to have at least a perpendicular vector component with respect to the optical axis to thereby displace an image.

Abstract: A zoom lens is disclosed comprising, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of negative refractive power, a fifth lens unit of positive refractive power and a sixth lens unit of negative refractive power, wherein, during zooming from the wide-angle end to the telephoto end, the air separations between the i-th and (i+1)st lens units are made to vary properly and the ratio of the focal length of the fourth lens unit to the longest focal length of the entire system is made to have a proper value. In particular, a zoom lens is disclosed wherein the second lens unit is made to decenter to stabilize the image.

Abstract: An afocal zoom lens system comprising a first positive lens unit, a second negative lens unit, a third positive lens unit and a fourth negative lens unit, wherein the first lens unit and the fourth lens unit are kept stationary, the second lens unit is moved so as to vary an airspace reserved between the first lens unit and the second lens unit, and an airspace reserved between the second lens unit and the third lens unit, the third lens unit is moved so as to vary an airspace reserved between the second lens unit and the third lens unit, and an airspace reserved between the second lens unit and the third lens unit, and an airspace reserved between the third lens unit and the fourth lens unit. The afocal zoom lens system for stereoscopic microscopes satisfies the following condition (1): 0.6<f3/f1<0.

Abstract: A zoom lens set with a fixed distance between lenses comprises at least one gradually changed curvature lens. The surface with a gradually changed curvature surfaces is locally limited by a suitable size pupil along an optical axis. In assembling, gradually changed curvature lenses are installed within a system so that the two lenses are retained within a fixed distance. Thereby, the or more gradually changed curvature lenses are adjusted and chosen by a local pupil to have a desired local curvature pairs or sets by relative transverse movement or rotation of the two or more lenses. Therefore, the focus of the system is changed to achieve the zooming purposed. By a simple design, the system can be completely matched with the zoom lens set with a fixed distance between the lenses so that the manufacturing cost of the system can be reduced effectively.

Abstract: A prism-type objective lens is provided for use in the pickup head of an optical disc drive capable of driving two types of optical discs such as a CD and a DVD. The prism-type objective lens allows the pickup head to be made more compact in size with reduced structural complexity, and also allows the pickup head to read data from two different types of optical discs. The prism-type objective lens includes a prism having a cross section substantially in the shape of a right triangle, a front aspherical plano-convex lens, and a rear aspherical plano-convex lens, where the planar surface of each lens is attached to one or the other of the leg sides of the prism. The hypotenuse side of the prism can be formed with two aperture areas where different reflective layers are coated. Alternatively, the hypotenuse side of the prism can be formed with a reflective HOE layer that allows the laser beam incident on it and reflected from it to be diffracted into two beams which are focused at different points.

Abstract: A zoom lens system has the first and second lens units. During zooming from a wide-angle end to a telephoto end, the lens units are moved to decrease a distance therebetween. The first lens unit has a positive refractive power. The second lens unit has a negative refractive power. The zoom lens system is provided with at least one surface having a power to diffract light.

Abstract: In a process for imaging image points of a video picture by means of a light bundle which is controlled in intensity with respect to the brightness of the image points and which is deflected and then projected onto a screen by a lens or a lens system, a variable focal length is provided for the lens, the lens system or a partial lens system of the lens system and an object-side focal point is maintained stationary when the focal length is varied.

Abstract: A projection zoom lens system is used in imaging and non-imaging modes for entertanment and architectural illumination, providing 8:1 zoom ratio in an imaging mode and 20:1 zoom ratio in a non-imaging mode. When coupled with a variable aperture iris, beam size control is obtained with 120:1 ratio. The lens system comprises four lens groups: a first group having a positive refractive power, a second group having a negative refractive power, a third group having a negative refractive power, and a fourth group having a positive refractive power. In the imaging mode, the third group is adjusted axially to vary magnification while the second group is adjusted axially to focus on the object. In the non-imaging mode, the second and third groups are brought into close proximity with each other and adjusted axially as a unit to vary magnification. The fourth group remains fixed and the first group can be adjusted axially to focus the image at different throw lengths.

Abstract: An offset reverse telephoto projection zoom lens 300 comprising a moving zoom group 302, a moving compensation group 304, and a fixed rear lens group 306. According to one embodiment of the projection lens, the zoom group 302 has four lenses, the compensation group 304 has four lenses, and the fixed rear group 306 has three lenses. An aperture stop 308 is located in the fixed rear group 306. The fixed rear group 306 has a small diameter which helps alleviate interference with illumination optics. Additionally, a fixed rear group 306 does not require zoom mechanisms at the rear of the lens 300 where space is at a premium.

Abstract: A zoom lens system that is free from parallax, is compact, and offers excellent optical performance has, from the object side, a positive first lens unit, a negative second lens unit, a positive third lens unit, and a negative fourth lens unit. The zoom lens system has a half-prism between the second lens unit and the third lens unit so that a light beam having passed through the second lens unit is split by reflection.

Abstract: The invention is directed to an afocal zoom system for a surgical microscope. The zoom system has an even number of members and is symmetrically configured.

Abstract: A zoom lens system includes two lens components, and zooming is performed by moving a first lens component. The zooming is performed along a zoom curve such that the first lens component is moved out so that in-focus condition is obtained at a subject distance predetermined with respect to each focal length. As the subject distance, an excess focal length or a subject distance where the far side of the depth of field is the maximum flash reachable distance or a subject distance where the near side of the depth of field is the shortest object distance or a subject distance where the object distance or the magnification is fixed is set according to the purpose.

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: A zoom lens system with vibration-reduction function, comprising, 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;a fourth lens group having a positive refractive power; anda fifth lens group having a negative refractive power;wherein, when zooming, each of the distances between the first and second lens groups, the second and third lens groups, the third and fourth lens groups, and the fourth and fifth lens groups, respectively, changes. The fourth lens group has a shift lens unit movable in a direction across an optical axis, has positive refractive power, and a fixed lens unit fixed in the direction across the optical axis.

Abstract: A lens system has nominal focal length and aberrations and includes a plurality of lens components defined by design parameter values and a special airspace distance. The lens system is characterized in design such that manufacturing deviations from the design parameter values cause a variation from the nominal focal length and a variation in at least one of the aberrations. Both of these deviations can be offset simultaneously by a single change in the special airspace distance.

Abstract: A zoom lens having the vibration-reduction function includes, in succession from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having negative refractive power, and a fourth lens unit having positive refractive power. The fourth lens unit includes, in succession from the object side, a front group having positive refractive power and a rear group having positive refractive power. During the focal-length change from the wide angle end to the telephoto end, the spacing between the first lens unit and the second lens unit is increased, the spacing between the second lens unit and the third lens unit and the spacing between the third lens unit and the fourth lens unit are non-linearly varied. At least one of the third lens unit and the front group in the fourth lens unit is provided for movement in a direction substantially orthogonal to the optical axis thereof.

Abstract: A zoom lens of the rear focus type is disclosed, comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of positive refractive power and a fifth lens unit of negative refractive power, wherein at least the second lens unit and the fourth lens unit are moved to vary magnification and the fourth lens unit is moved to effect focusing, and wherein the third lens unit comprises, in order from the object side to the image side, a positive lens and a negative lens having a strong concave surface facing the image side.

Abstract: In order to reduce complexity and cost of fabrication of zoom lenses, the real image forming lens group module at the front of the zoom lens is replaced with a two-element group where one of the elements has a diffractive lens on a curved surface thereof instead of the usually cemented doublet of the front group, but with substantially the same aberrations as a front group with three elements, including a cemented doublet. Aberrations (chromatic and monochromatic) produced by the first and second groups remain corrected by the combination of these groups over the zoom range of the lens. A second group housing two-elements, one of which has a curved surface on which a diffractive lens is provided, may be also be used to replace the three-element second lens group and particularly the cemented doublet thereof.

Abstract: A projection optical system. The system (10) contains two movable lens groups, a zoom lens group (20) and a compensator group (18). The compensator group (18) includes a movable aperture stop (21), thereby eliminating the need for a variable aperture stop. Both groups contain at least one aspheric lens element (22, 32) for elimination of aberrations. The compensator group has a positive power, with the zoom group having a negative power, resulting in a reverse telephoto configuration.

Abstract: A zoom lens system has at least three lens groups in which two lens groups are moved together during the zooming operation. One of the two lens groups moved has a small degree of contribution to the variation of magnification and is referred to as lens group .alpha. The other lens group moved has a large degree of contribution to the variation of magnification and is referred to as lens group .beta.. Lens groups .alpha. and .beta. have focusing sensitivities K.alpha. and K.beta. of different signs on the telephoto extremity, and the relationships:12<.vertline.K.beta..vertline., (1)and-0.5<K.alpha./K.alpha.<-0.1.