Abstract: An imaging lens device has an imaging lens system that forms an optical image and an image sensing device that converts the optical image formed by the imaging lens system into an electronic signal. The imaging lens system includes two lens elements each made of a homogeneous material and having a positive optical power, and fulfills the following condition: 1.25<L/f<2.00, where L is the distance from the most object side lens surface to the image plane, and f is the overall focal length of the lens system.

Abstract: A zoom lens of the negative lead type includes comprises, in order from an object side, a first lens unit of negative refractive power and a second lens unit of positive refractive power, variation of magnification being effected by varying a separation between the first lens unit and the second lens unit, the zoom lens satisfying the following conditions: 3?NL1?4 NL2?NL1 where NL1 and NL2 are numbers of lens elements which constitute the first lens unit and the second lens unit, respectively.

Abstract: An observation optical system including an objective optical part which forms an image of an object, an image inverting part which converts an image formed by said objective optical part into an erect image, and an eyepiece optical part which guides the erect image converted by said image inverting part to an observer. The objective optical part has a first lens unit with a negative power and a second lens unit with a positive power arranged from an object side in the order named, and said second lens unit is movable in a direction including a component perpendicular to an optical axis to stabilize an image.

Abstract: A compact two-group zoom lens that corrects aberrations in the visible and the near infrared regions and that provides a comparatively high zoom ratio includes, in order from the object side, a first lens group of negative refractive power and a second lens group of positive refractive power. The first lens group includes, in order from the object side, first and second negative meniscus lens elements having convex surfaces on the object side, a biconcave lens element, and a positive lens element. The second lens group includes, in order from the object side, a positive lens component which may be a lens element, a negative/positive doublet component, and a negative lens component which may be a lens element. Aspheric lens surfaces are disclosed. Certain conditions are satisfied to control aberrations in both the visible and the near infrared and to ensure a sufficient back focus distance.

Abstract: The invention relates to a compact two-group zoom optical system which has an angle of view of 70° or greater at the wide-angle end and satisfactory image-formation capability all over the zoom range while maintaining a zoom ratio of 3 or greater. The zoom optical system comprises a first lens group G1 having positive refracting power and a second lens group G2 having negative refracting power. For zooming from the wide-angle end to the telephoto end, the respective lens groups move toward the object side while the spacing between the first lens group G1 and the second lens group G2 becomes narrow.

Abstract: A zoom optical system includes at least two optical-element groups and a variable optical-property optical element. The two optical-element groups are movable in a magnification change and have a magnification varying function or a compensating function for compensating for a shift of an image surface caused by the magnification change. The optical element has a focusing function and is disposed on the image side of the optical-element groups. 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: A projector lens system includes a negative first lens group and a positive second lens group. The first lens group comprises a first lens element that is formed as a negative meniscus lens element, a positive or negative second lens element, a negative third lens element, a positive fourth lens element that is cemented to or separated from the third lens element, and a negative fifth lens element. The first lens group satisfies condition (1) with respect to the refractive power thereof, and satisfies condition (2) with respect to the refractive power of the negative first lens element of the negative first lens group: 0.6<fw/|fI|<1.0(fI<0)??(1) 0.3<fI/f1,1<0.7??(2) wherein fw: focal length of the entire projector lens system at the wide-angle extremity; fI: the focal length of the negative first lens group; and f1,1: the focal length of the negative first lens element of the negative first lens group.

Abstract: According to one aspect of the present invention, a zoom lens system includes, in order from an object along an optical axis, a first lens group having negative refractive power, and a second lens group having positive refractive power. A distance between the first lens group and the second lens group decreases when the state of lens group positions varies from a wide-angle end state to a telephoto end state. The second lens group is composed of, in order from the object, a first lens having positive refractive power, a first cemented lens having negative refractive power, and a second cemented lens having positive refractive power. The first cemented lens in the second lens group is constructed by a positive lens cemented with a negative lens. The second cemented lens in the second lens group is constructed by a negative lens cemented with a positive lens.

Abstract: A wide-angle lens system having a long back focal length, disposed in front of a ?? CCD camera and the focal length (f) for all lens groups is 3.0 mm, the F-number is 3.0 and the half-field angle is 46°. The following conditions are met by the first lens group: 1?d/d3<1.2; R3/R2=0.99; and d2/f=0.03. Here, (d) indicates the thickness of the second lens along the normal line at a given distance from the optical axis within the maximum effective diameter of the object side convex surface of the lens. d3 is the thickness of the second lens along the optical axis.

Abstract: A zoom optical system includes at least two optical-element groups and a variable optical-property optical element. The two optical-element groups are movable in a magnification change and have a magnification varying function or a compensating function for compensating for a shift of an image surface caused by the magnification change. The optical element has a focusing function and is disposed on the image side of the optical-element groups. 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: A small-sized and light weight zoom lens achieving high optical performance, a wide angle of view, and a high magnification, is disclosed. The zoom lens comprises, in order form the object side, a first lens unit with positive optical power, a second lens unit with negative optical power having a magnification varying function, and at least one other lens unit. The first lens unit includes, in order from the object side, a first negative lens element the object side surface of which is concave toward the object side, a second negative lens element, and a positive lens element.

Abstract: A miniature image capturing lens includes an aperture diaphragm; and a lens system consisting of a first lens having a positive refracting power in which a convex surface of the first lens is directed toward an image; and a meniscus-shaped second lens in which a concave surface of the meniscus is directed toward an object. The aperture diaphragm, the first lens and the second lens are aligned in this order from the object side, the fist and second lenses have at least one aspherical surface. The following conditional formulas are satisfied: 0.50<f1/f<0.80 0.30<(R2+R1)/(R1−R2)<1.20 where f1 is a focal length of the first lens, f is a focal length of the entire image capturing lens, R1 is a radius of curvature of the object side surface of the first lens, and R2 is a radius of curvature of the image side surface of the second lens.

Abstract: A wide-angle zoom lens is disclosed having only two lens groups, of negative and positive refractive power in order from the object side, respectively, and which provides an image angle at the wide-angle end of at least 100°. Zooming is performed by moving the first lens group and the second lens group along the optical axis. The first lens group is formed of, in sequential order from the object side, a negative meniscus lens element with its convex surface on the object side, two negative lens elements, and a positive lens element. The second lens group is formed of, in sequential order from the object side, two positive lens elements, a biconcave lens element, and two positive lens elements. Various conditions are preferably satisfied so as to minimize aberrations and make the zoom lens compact and easy to manufacture.

Abstract: A compact two-group zoom lens that corrects aberrations in the visible and the near infrared regions and that provides a comparatively high zoom ratio includes, in order from the object side, a first lens group of negative refractive power and a second lens group of positive refractive power. The first lens group includes, in order from the object side, first and second negative meniscus lens elements having convex surfaces on the object side, a biconcave lens element, and a positive lens element. The second lens group includes, in order from the object side, a positive lens component which may be a lens element, a negative/positive doublet component, and a negative lens component which may be a lens element. Aspheric lens surfaces are disclosed. Certain conditions are satisfied to control aberrations in both the visible and the near infrared and to ensure a sufficient back focus distance.

Abstract: A zoom lens is disclosed that is formed of only two lens groups. The first lens group includes, from the object side, a plastic lens element having negative refractive power and an aspheric surface, and a lens element having positive refractive power. The second lens group includes, from the object side: a biconvex lens element having an aspheric surface; a lens element having negative refractive power, a smaller curvature on its object side, and with its image-side surface joined to a biconvex lens element. The zoom lens satisfies specified conditions to: (a) allow for ease of manufacture and assembly while maintaining favorable correction of various aberrations, (b) assure that the zoom lens is compact in both the operational and retracted positions, (c) assure that the zoom lens is not easily damaged, and (d) assure that the optical performance is well-maintained despite changes in ambient conditions, such as temperature.

Abstract: The invention relates to a compact, high-performance yet wide-field real image type zoom finder comprising a positive objective optical system Ob and a positive eyepiece optical system Ep and further including an image-inverting means for erecting an real image formed by the objective optical system. The objective optical system Ob comprises a plurality of moving groups G2 and G3, and the eyepiece optical system Ep comprises positive reflecting surfaces, at least one of which is defined by a rotationally asymmetric surface, and satisfies conditions 1.25<dEP/fOC<2.0 and 0.5<lOC/fOC<1.3 where dEP is the distance as measured along an axial chief ray from a final surface to an eye point of the eyepiece optical system, fOC is the focal length of the eyepiece optical system, and lOC is the length as calculated on an air basis and measured along an axial chief ray from an intermediate image-formation plane to the final surface of the eyepiece optical system.

Abstract: According to one aspect of the present invention, a zoom lens system includes, in order from an object along an optical axis, a first lens group having negative refractive power, and a second lens group having positive refractive power. A distance between the first lens group and the second lens group decreases when the state of lens group positions varies from a wide-angle end state to a telephoto end state. The second lens group is composed of, in order from the object, a first lens having positive refractive power, a first cemented lens having negative refractive power, and a second cemented lens having positive refractive power. The first cemented lens in the second lens group is constructed by a positive lens cemented with a negative lens. The second cemented lens in the second lens group is constructed by a negative lens cemented with a positive lens.

Abstract: A wide-angle zoom lens is formed of a first lens group having a negative refractive power, a stop, and a second lens group having a positive refractive power. Magnification is varied by moving the second lens group to the object side when zooming from the wide-angle end to the telephoto end. What would otherwise be a shift of the image plane with the zooming is corrected by moving the first lens group to the image side when zooming from the wide-angle end to the telephoto end. A lens in the second lens group has at least one surface that is aspherical and is positioned on the image side of a lens in the second lens group having positive refractive power and a convex surface on the object side.

Abstract: A zoom lens system includes at least two lens groups, and a negative first lens group is positioned at the most object-side of the zoom lens system. The negative first lens group includes a negative sub-lens group and a positive sub-lens group. The positive sub-lens group includes a positive lens element and a rearmost lens element of the negative first lens group. The rearmost lens element includes a plastic lens element having at least one aspherical surface.

Abstract: A lens barrel includes a first frame member supporting a first lens group, a second frame member supporting a second lens group and being capable of movable relative to the first frame member along an optical axis, a cam follower in the first frame member, a cam frame member having a cam groove engaged with the cam follower to permit the first frame member to be movable along the optical axis, a contact portion which is provided for the second frame member and can come into contact with the cam follower, and a pushing member pushing the second frame member in the direction the cam follower comes into contact with the contact portion. The pushing member pushes the second frame member and the contact portion comes into contact with the cam follower. Thus, the position of the second lens group with respect to the first lens group can be restricted.

Abstract: A focus lens and a zoom lens group having a first zoom lens and a second zoom lens are controlled separately from one another in an internal-focus camera. The positions of the focus lens and the second zoom lens in the zoom lens group are tracked, and are controlled to approach no closer to one another than a minimum safe distance to avert collisions between the focus lens and the second zoom lens.

Abstract: A variable magnification lens performs a magnification change by changing a distance between a first lens unit G1 having a positive refracting power and a second lens unit G2 having a negative refracting power, which are arranged in this order from the object side. The first lens unit G1 includes, in order from the object side, a sub-unit 1a, an aperture stop S, and a sub-unit 1b. All lens elements constituting the first lens unit G1 are arranged with intervening air spaces between one another. The variable magnification lens satisfies the following conditions: 1.1<FLw/IH<1.35 0.80<TLt/FLt<0.94 where FLw is a focal length in a wide-angle end position, FLt is a focal length in a telephoto end position, IH is a maximum image height, and TLt is a distance, in the telephoto end position, from a first surface to an image surface along an optical axis.

Abstract: A zoom lens system is disclosed. The zoom lens system forms a final image of an object and a first intermediate real image between the object and the final image. The zoom lens system includes a first optical unit located between the object and the first intermediate real image. The first optical unit comprises at least one optical subunit which is moved to change the size (magnification) of the first intermediate real image. The zoom lens system also includes a second optical unit located between the first intermediate real image and the final image, at least a portion of which is moved to change the size (magnification) of the final image. The zoom lens system provides a wide zoom range of focal lengths with continuous zooming between the focal lengths and optional image stabilization.

Abstract: A variable-focus lens system includes a negative front lens group, and a positive rear lens group. The focal length of the variable-focus lens system is varied by changing the distance between the front and said rear lens groups. The lens system satisfies the following conditions: −3.0<fx/Fw<−2.5 3.0<fy/Fw<3.5 wherein fx designates the focal length of the front lens group, which is less than zero; fy designates the focal length of the rear lens group, which is greater than zero; and Fw designates the focal length of the entire variable-focus lens system at the short focal length extremity.

Abstract: A negative-lead type zoom lens has a diffractive optical element and is led by a lens unit having a negative optical power. In this zoom lens, various kinds of aberration including chromatic aberration are excellently corrected by properly setting the lens configuration of each lens unit so as to achieve high optical performance over the entire range of a variable power while the entire lens system is miniaturized and designed to have a wide angle. The zoom lens according to the present invention is suitable for a zoom lens with a wide angle including a wide-angle region that is a focal length of substantially 28 mm on a 35 mm single lens reflex camera basis.

Abstract: The invention provides a zoom lens that comprises a reduced number of lens elements, is compact and simplified, and has high image-formation capability, thereby achieving thorough size reductions in video cameras or digital cameras, and an electronic imaging system using the same. The zoom lens comprises, in order from its object side, a lens group A (G1) having negative refracting power and a lens group B (G2) having positive refracting power. For zooming, the lens groups A and B are designed to move. The lens group B is composed of three meniscus lenses, each convex on its object side.

Abstract: A wide-angle zoom lens is formed of a first lens group having a negative refractive power, a stop, and a second lens group having a positive refractive power. Magnification is varied by moving the second lens group to the object side when zooming from the wide-angle end to the telephoto end. What would otherwise be a shift of the image plane with the zooming is corrected by moving the first lens group to the image side when zooming from the wide-angle end to the telephoto end. A lens in the second lens group has at least one surface that is aspherical and is positioned on the image side of a lens in the second lens group having positive refractive power and a convex surface on the object side.

Abstract: The present invention relates to a digital still camera that is compatible with an increasing number of pixels and uses a zoom lens having a high zoom ratio yet compact, simple construction, wherein chromatic aberration of the zoom lens are reduced and the zoom lens is kept against the influences of chromatic aberrations. The zoom lens comprises a lens group G2 having negative refracting power and at least one lens group G3 located on the image side of G2 and having positive refracting power. Upon zooming, the spacing between the negative lens group G2 and the positive lens group G3 changes. The positive lens group G3 includes two doublet components, in each of which a positive lens element and a negative lens element are cemented together in order from the object side of G3. The doublet component located on the image side of G3 has a meniscus form concave on its image side.

Abstract: A lens apparatus includes four lens groups and a plurality of barrels with grooves that guide and drive the lens frames of the four lens groups in order to achieve a high zoom ratio and retraction of the lens apparatus into a camera body when the lens apparatus is not in use. Two sets of three guide grooves in a fixed barrel and three cam grooves in a cam barrel are unequally spaced around the circumference of the barrels so as to provide more room for an additional groove in the cam barrel. Some of the lens frames are fully supported by pins in the grooves and some of the lens frames are partially supported by guide rods in the lens apparatus. A single guide rod helps support two lens frames in order to save space in the lens apparatus.

Abstract: A wide-angle zoom lens is disclosed having only two lens groups, of negative and positive refractive power in order from the object side, respectively, and which provides an image angle at the wide-angle end of at least 100°. Zooming is performed by moving the first lens group and the second lens group along the optical axis. The first lens group is formed of, in sequential order from the object side, a negative meniscus lens element with its convex surface on the object side, two negative lens elements, and a positive lens element. The second lens group is formed of, in sequential order from the object side, two positive lens elements, a biconcave lens element, and two positive lens elements. Various conditions are preferably satisfied so as to minimize aberrations and make the zoom lens compact and easy to manufacture.

Abstract: A two-group zoom lens includes, in order from the object side, a first lens group that includes a negative lens component formed of a negative plastic lens element having at least one aspheric lens surface and a positive lens component, and a second lens group that includes a diaphragm, a positive lens component that is formed of a positive plastic lens element having at least one aspheric lens surface, and a negative lens doublet component. The first lens group and at least a part of the second lens group is movable along the optical axis for zooming, and either the first lens group or a lens component of the second lens group moves independently of the other lens components of the second lens group for focusing. Except for the negative lens doublet component, each lens component may be a lens element. The lens components and lens elements satisfy certain conditions.

Abstract: The relay optical system comprises, in order from the intermediate image position I toward the the exit pupil EXP side, a first unit G1 having a negative refracting power and a second unit G2 having a positive refracting power, wherein the distance from the rearmost surface of the second unit to the exit pupil position is at least 30 mm. The relay optical system allows a photographing apparatus to be mounted on a microscope without the microscope and the photographing apparatus excluding each other from their predetermined positions.

Abstract: A zoom lens has a lens group of negative refractive power at the enlarging end and a lens group of positive refractive power at the reducing end, both of which are fixed during zooming. The lens group of negative refractive power includes two lens components of negative refractive power, and at least one of the lens groups includes a thin plastic lens element with a lens surface bonded to a lens surface of a glass lens element, with the other lens surface of the plastic lens element having an aspheric shape. The lens group of negative refractive power consists of lens elements of negative refractive power. One of the two lens components is at the enlarging end of the zoom lens and includes a meniscus lens element of negative refractive power. The other lens component is adjacent the one lens component and is a biconcave lens component.

Abstract: A wide-angle zoom lens includes a front lens unit with positive refracting power and a rear lens unit with negative refracting power so that spacing between the front lens unit and the rear lens unit is changed to thereby vary the magnification of the zoom lens. In this case, the rear lens unit has a first lens component with positive refracting power and a second lens component with negative refracting power so that an aspherical surface is not included in any lens component, and satisfies the following conditions: 2.5<fT/fW<5 0.7<tan &ohgr;w<1.5 where fT is the focal length of the entire system of the wide-angle zoom lens at the telephoto position, fW is the focal length of the entire system of the wide-angle zoom lens at the wide-angle position, and &ohgr;w is a half angle of view at the wide-angle position.

Abstract: A telescopic zoom lens system has a minimum magnification thereof is more than 2, and includes a positive objective lens group, and a positive eyepiece lens group, in this order from the object. Further, a zooming lens group which is made moveable along the optical axis upon zooming is positioned on the side of the object with respect to the primary image forming plane of the objective optical system.

Abstract: A soft-focus lens system includes a master lens group and a soft-focus lens group. The soft-focus lens group includes a positive sub lens group and a negative sub lens group. The positive sub lens group and the negative sub lens group are moved to set the normal photographing mode or the soft-focus photographing mode. Each of the sub lens groups is arranged to move with respect to the master lens group and the other of the sub lens groups so that the focal point and the focal length are not substantially varied before and after the switching of the soft-focus photographing mode to the normal photographing mode or vice versa.

Abstract: A soft-focus lens system includes a master lens group and a soft-focus lens group. The soft-focus lens group includes a positive sub lens group and a negative sub lens group. The positive sub lens group and the negative sub lens group are moved to set the normal photographing mode or the soft-focus photographing mode. Each of the sub lens groups is arranged to move with respect to the master lens group and the other of the sub lens groups so that the focal point and the focal length are not substantially varied before and after the switching of the soft-focus photographing mode to the normal photographing mode or vice versa.

Abstract: A standard photographic lens is disclosed that includes a front lens group, a diaphragm stop, and a rear lens group, in order from the object side. The front lens group is formed of a negative meniscus lens with its convex surface on the object side, and a positive meniscus lens with its convex surface on the object side. The rear lens group is formed of a third lens element of negative refractive power with a concave surface on the object side, a fourth lens element of positive refractive power with a convex surface on the image side, and a fifth lens element, of meniscus shape with its concave surface on the image side. Organic material is preferably used for the second and third lens elements. Various conditions are satisfied so as to provide a lens having a bright image with favorably corrected aberrations.

Abstract: A zoom lens is provided. The zoom lens includes a positive power first lens group having a first lens element and a second lens element, and a negative power second lens group having a third lens element. The first lens element can be made from plastic having either or both of its surfaces aspheric with a meniscus shape concave or convex to an object side. The first lens group includes a variable iris having a mechanical aperture stop positioned between the first lens element and the second lens element.

Abstract: The object of the present invention is to provide a catadioptric imaging system, or the like, which is capable of obtaining a desired image-side NA and an image circle without increasing the size of a reflecting mirror with a smaller number of lenses. This catadioptric imaging system comprises a first imaging optical system and a second imaging optical system, wherein the first imaging optical system is provided with a positive first lens group, an aperture stop, and a positive second lens group in the order from the object side, and the second imaging optical system is provided with a primary mirror comprising a concave first reflecting surface having a first radiation transmitting portion at the center thereof, and a secondary mirror comprising a second reflecting surface having a second radiation transmitting portion at the center thereof.

Abstract: An endoscope objective optical system includes a negative first lens group, a positive second lens group, and an imaging device, in this order from the object.

Abstract: The invention relates to a two-group zoom lens of +− construction, which, albeit having a high zoom ratio, is reduced in length not only at the wide-angle end but also at the telephoto end and has a low telephoto ratio at the telephoto end where the length of the system becomes longest. The zoom lens comprises a first lens group G1 having positive refracting power and a second lens group G2 having negative refracting power. For zooming from the wide-angle end to the telephoto end of the system, each lens group moves toward the object side while the spacing between the first and second lens groups G1 and G2 becomes narrow. Specific conditions for the focal length of the second lens group G2, the amount of movement of the second lens group G2 and the zoom ratio shared by the second lens group G2 are satisfied.

Abstract: A taking lens device has a zoom lens system, including a plurality of lens units, for forming an optical image of an object with variable magnification achieved by varying the distances between the lens units, and an image sensor for converting the optical image formed by the zoom lens system into an electric signal. The zoom lens system includes, from the object side to the image side a first lens unit that has a negative optical power, that is composed solely of a single negative lens element having a sharper curvature on the image side than on the object side thereof, and that is moved along the optical axis during zooming, and a second lens unit that is disposed with an aerial distance secured between itself and the first lens unit, that has a positive optical power, and that is moved along the optical axis during zooming. Moreover, the following conditional formulae are fulfilled: 0.3<t1/Y′<1.5 and 1.

Abstract: An observation optical system including an objective optical part which forms an image of an object, an image inverting part which converts an image formed by said objective optical part into an erect image, and an eyepiece optical part which guides the erect image converted by said image inverting part to an observer. The objective optical part has a first lens unit with a negative power and a second lens unit with a positive power arranged from an object side in the order named, and said second lens unit is movable in a direction including a component perpendicular to an optical axis to stabilize an image.

Abstract: A negative-lead type zoom lens has a diffractive optical element and is led by a lens unit having a negative optical power. In this zoom lens, various kinds of aberration including chromatic aberration are excellently corrected by properly setting the lens configuration of each lens unit so as to achieve high optical performance over the entire range of a variable power while the entire lens system is miniaturized and designed to have a wide angle. The zoom lens according to the present invention is suitable for a zoom lens with a wide angle including a wide-angle region that is a focal length of substantially 28 mm on a 35 mm single lens reflex camera basis.

Abstract: A wide-angle zoom lens is disclosed having only two lens groups, of negative and positive refractive power in order from the object side, respectively, and which provides an image angle at the wide-angle end of at least 100°. Zooming is performed by moving the first lens group and the second lens group along the optical axis. The first lens group is formed of, in sequential order from the object side, a negative meniscus lens element with its convex surface on the object side, two negative lens elements, and a positive lens element. The second lens group is formed of, in sequential order from the object side, two positive lens elements, a biconcave lens element, and two positive lens elements. Various conditions are preferably satisfied so as to minimize aberrations and make the zoom lens compact and easy to manufacture.

Abstract: An image-capturing lens is formed of front and rear lens groups having negative and positive refractive power, respectively, in order from the object side. The rear lens group is formed of, in relative sequential order from the most object side of the rear lens group, a biconvex lens element that is cemented to a biconcave lens element, a biconvex lens element, and a biconvex lens element. A specified condition is satisfied so as to make the cemented lens of the rear lens group insensitive to de-centering errors which may occur either in making the cemented lens or in assembling the image-capturing lens.

Abstract: The object of the present invention is to provide a negative-positive, two-group type zoom lens system having a uniquely high zoom ratio of about 3.5, and having relatively small diameter and compactness with small number of lens element. According to one aspect, a zoom lens system includes, in order from an object-side, a first lens group having negative refractive power and a second lens group having positive refractive power. Zooming is carried out by varying the space between the first lens group and the second lens group. The first lens group includes, in order from the object side, a negative lens group G1F composed of one or two negative lens element, and a positive lens group G1R. The following conditional expressions are satisfied: 4.5≦|X2|·ft/fw2≦15  (1) 0.7≦|f1|/(fw·ft)½≦1.

Abstract: A retro-focus-type camera lens is disclosed that is formed of, in order from the object side: a front lens group having negative refractive power, a diaphragm, and a rear lens group having positive refractive power. The front lens group is formed of, in order from the object side, a positive lens element and two negative lens elements, and the rear lens group is formed of, in order from the object side, a positive lens element, two sets of lens elements that are cemented together to form two joined lenses, and a positive lens element. Various conditions are preferably satisfied in order to provide a lens having an image angle of about 38°, an F number of about 1.4, and which suppresses the occurrence of color shading while providing a sufficient back focus to insert a color separation optical system between the retro-focus-type camera lens and the image plane.

Abstract: The invention relates to a compact two-group zoom optical system which has an angle of view of 70° or greater at the wide-angle end and satisfactory image-formation capability all over the zoom range while maintaining a zoom ratio of 3 or greater. The zoom optical system comprises a first lens group G1 having positive refracting power and a second lens group G2 having negative refracting power. For zooming from the wide-angle end to the telephoto end, the respective lens groups move toward the object side while the spacing between the first lens group G1 and the second lens group G2 becomes narrow. The first lens group G1 consists of a first lens unit U1 having negative refracting power, a second lens unit U2 having positive refracting power and a third lens unit U3 having positive refracting power. Each lens unit consists of a single lens or a doublet.