Abstract: A zoom lens includes, sequentially from an object side, a first lens group that is negative; and a second lens group that is positive, where focal length is varied by varying a distance between the first lens group and the second lens group. The first lens group includes, from the object side, a first lens that is a negative biconcave lens having at least one aspherical surface, and a second lens that is a positive meniscus lens having a convex surface facing toward the object side and at least one aspherical surface, and a first condition 0.8<|f1/f2|<1.0 and a second condition 0.5<|r2/f1|<0.8 are satisfied, where f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, r2 is radius of curvature of a surface of the first lens in the first lens group, the surface facing toward an image.

Abstract: A zoom lens system includes a negative first lens group, a positive second lens group, and a positive third lens group, in this order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, the distance between the negative first lens group and the positive second lens group decreases, and the distance between the positive second lens group and the positive third lens group increases. The negative first lens group includes a negative first lens element, a negative second lens element having a weaker negative refractive power, and a positive third lens element, in this order from the object. The second lens element of the negative first lens group satisfies the following condition: 0<(ra?rb)/(ra+rb)<0.

Abstract: A zoom lens including a first lens group with a negative refractive power and a second lens group with a positive refractive power is provided. The first lens group is composed of a first lens, a second lens, and a third lens. Refractive powers of the first lens, the second lens, and the third lens are respectively negative, negative, and positive. Moreover, the second lens group is disposed between the first lens group and an image side. The second lens group is composed of a fourth lens, a fifth lens, and a sixth lens. Refractive powers of the fourth lens, the fifth lens, and the sixth lens are respectively positive, negative, and positive. The first lens group and the second lens group are capable of moving between an object side and the image side. The zoom lens has advantages of wide angle and small volume.

Abstract: A zoom lens includes a most object-side lens unit remaining fixed on the optical axis when the magnification of the zoom lens is changed and a focusing operation is performed; a most image-side lens unit remaining fixed when the focusing operation is performed; and a plurality of moving lens units lying between the most object-side lens unit and the most image-side lens unit, moved along the optical axis when the magnification is changed. The most object-side lens unit includes, in order from the object side, a negative lens component, a reflective optical component having a reflecting surface for bending the optical path, and a positive lens component. The most image-side lens unit has at least one aspherical surface. An electronic imaging device includes an electronic image sensor located on the image side of the zoom lens.

Abstract: A zoom lens including, in order from an object side to an image side, a first group having a negative focal length, a second group having a positive focal length, a third group having a negative focal length, a fourth group having a positive focal length, and an aperture stop between the second group and the third group, wherein when changing a magnification from a short focus end to a long focus end, at least the second group monotonically moves from the image side to the object side such that a distance between the first group and the second group decreases, and a distance between the second group and the third group increases, and the third group includes a three-cemented lens having a negative lens, a positive lens and a negative lens in order from the object side.

Abstract: The present invention is directed to a wide-angle zoom lens that attains the field of view ranging from 80 to 115 degrees in field angle with the zooming power of 2× or even higher, and that is capable of approximately compensating for various types of aberration such as spherical aberration, aberration of distortion, astigmatism and the like. The wide-angle zoom lens of multi groups of lens pieces, namely, a 1st lens group of negative refractivity, a 2nd lens group of negative refractivity, and a 3rd lens group of positive refractivity varies the power from the wide-angle end to the telephoto end with the 1st and 2nd lens groups coming closer to each other, and the 2nd and 3rd lens groups being varied in interval therebetween. The zoom lens attains the widest field of view of 80 degrees or over in field angle in the relations as expressed in the following formula: 2.

Abstract: There is provided a zoom optical system having lens elements produced with less difficulty i.e. with substantially the same skill level as the conventional arrangement, with sufficient miniaturization. The zoom optical system includes a first lens group having a negative optical power, and a second lens group having a positive optical power in the order from the object side, the distance between the first lens group and the second lens group being decreased in zooming from a wide angle end to a telephoto end. The first lens group is constituted of a negative lens element and a positive meniscus lens element. The second lens group is constituted of a biconvex positive lens element and a negative meniscus lens element.

Abstract: A zoom lens includes a first lens unit having a negative optical power located closest to an enlargement side. In the zoom lens, a focal length of the zoom lens at a wide-angle end (fw) and a focal length of the first lens unit (f1) satisfy the following condition: ?2.50<f1/fw<?1.36.

Abstract: Provided are an imaging optical system in which chromatic aberrations are excellently corrected across the entire screen to realize high optical performance, and an optical apparatus including the imaging optical system. In an imaging optical system of which a back focus is longer than a focal length, a lens unit located in a reduction-conjugate side of an aperture stop includes at least one positive lens. A partial dispersion ratio and an Abbe number of the positive lens are set such that a refractive index, a position, and a power satisfy a suitable relationship.

Abstract: An observation optical system has a negative lens unit including a cemented lens, arranged at the most object-side position; an annular reflecting mirror placed on the image side of the negative lens unit, with a reflecting surface facing the image side; and an imaging lens unit arranged on the image side of the negative lens unit and the annular reflecting mirror.

Abstract: A zoom lens system comprising a first lens unit having negative power, a second lens unit having positive power and a third lens unit having positive power, wherein: the first lens unit comprises a first lens element having a concave surface at least on the image side and negative power and a second lens element having a convex surface at least on the object side and positive power; the second lens unit comprises a cemented lens element fabricated by two lens elements having optical power of mutually different signs and one single lens element; in zooming, all of the lens units move along an optical axis; and conditions (1): 5.0<?iW<20.0 and (I-2): n11?1.9 (where, 3.

Abstract: A zoom lens includes, in order from an object side, a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power. At least the first and second lens groups are movable during a change from a wide-angle end state in which a focal length becomes shortest to a telephoto end state in which the focal length becomes longest. The first lens group is constructed of a glass lens and a plastic lens, the glass lens being positioned on the object side and having a negative power, the plastic lens being positioned on an image side and having a positive power. The second lens group includes a single plastic lens having a negative power. The third lens group includes at least one plastic lens having a positive power. The lenses are satisfied predetermined conditions.

Abstract: An image pickup optical system includes a first-lens unit having negative refractive power; a second-lens unit having positive refractive power and being disposed closer to an image side than the first-lens unit; an aperture; and a diffraction optical part provided on the joint surface of a first-cemented lens closer to the image side than the aperture. The focal length of the whole system, the Abbe number of the negative lens of a second-cemented lens closer to the image side than the aperture, the focal length within the air, the Abbe number of a negative lens closer to an object side than the aperture, the average value between the curvature radius closest to the object side and the curvature radius closest to the image side of the first-cemented lens including the diffraction optical part, the curvature radius of the diffraction optical part, and so forth, are set appropriately.

Abstract: A two-group zoom projection lens is provided and includes: in order from a magnification side, a first lens group having a negative refractive power; and a second lens group having a positive refractive power, the second lens group including a front group and a rear group in order from the magnification side, the front group including a group having at least two positive lenses and a group having at least one negative lens in order from the magnification side, the rear group including a group having at least one negative lenses and a group having at least two positive lenses in order from the magnification side. The front group includes a negative lens having a concave surface directed toward the magnification side, the rear group includes a negative lens having a concave surface directed toward a reduction side, and the projection lens satisfies conditional expressions specified in the specification.

Abstract: A zoom lens system includes, in order from an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. During zooming from a wide-angle end to a telephoto end, a space between the first lens unit and the second lens unit narrows, at least the second lens unit moves only toward the object side, and the third lens unit is constituted of one positive lens.

Abstract: The present zoom lens system comprises a plurality of lens units including at least: a front lens unit having negative optical power; and a rear lens unit having positive optical power, arranged on the image side of the front lens unit, and composed of a plurality of lens elements; wherein magnification change is performed by changing an interval between the individual lens units, wherein the rear lens unit comprises: a rear A lens unit capable of moving in a direction perpendicular to an optical axis; and a rear B lens unit that is arranged on the image side of the rear A lens unit and that can move in an optical axis direction in such a manner that an interval relative to the rear A lens unit in the optical axis direction is changed, and wherein focusing adjustment during variation of the object distance is achieved by changing the interval between the rear A lens unit and the rear B lens unit.

Abstract: In an image forming optical system having a positive lens group, a negative lens group, and an aperture stop, the negative lens group is disposed at an image side of the of the aperture stop, the negative lens group has a cemented lens which is formed by cementing a plurality of lenses, and in a rectangular coordinate system in which, a horizontal axis is let to be Nd and a vertical axis is let to be ?d, when a straight line indicated by Nd=?×?d+? (where, ?=?0.017) is set, Nd and ?d of at least one lens forming the cemented lens are included in both of areas namely, an area which is determined by a line when a lower limit value is in a range of a following conditional expression (1), and a line when an upper limit value is in a range of the following conditional expression (1), and an area determined by following conditional expressions (2) and (3). 1.45<?<2.15??(1) 1.30<Nd<2.20??(2) 3<?d<12??(3) Here, Nd denotes a refractive index, and ?d denotes an Abbe's number.

Abstract: A zoom lens system consists, in order from an object side to an image-forming side, of a first negative lens group G1, a second positive lens group G2, and a third positive lens group G3. The first lens group G1 consists of one negative lens and one positive lens, the second lens group G2 consists of a cemented lens composed of a positive lens and a negative lens, and one meniscus lens that is concave on the image-forming side, the third lens group G3 consists of a single positive lens, and a combined focal length f2 of the second lens group, a focal length Lf23 of the meniscus lens of the second lens group, a combined focal length fw of the zoom lens system at a wide angle end, a combined focal length f3 of the third lens group, a radius of curvature Ro of an object side surface of the positive lens in the cemented lens, and a radius of curvature Ri of an image-forming side surface of the positive lens in the cemented lens satisfy the following conditions 0<|f2/Lf23|<0.3 ?2.0<Ri/Ro<?1.0 0.

Abstract: The projection zoom lens system includes a negative first lens group, a positive second lens group, a third lens group, a positive fourth lens group, a fifth lens group, and a positive sixth lens group. The lens system is nearly telecentric on a reduction side. During zooming, the second to fifth lens groups are moved while the first and six lens groups remain stationary. The third lens group includes a positive lens LP having a convex surface directed to a magnification side, and a negative lens LN having a concave surface which is directed to the reduction side and has a curvature stronger than a magnification-side surface of the negative lens LN. The conditional expression of 5.0?|fG3/RLN-2| is satisfied. Here, fG3 denotes a focal length of the third lens group, and RLN-2 denotes a radius of curvature of the reduction-side surface of the negative lens LN.

Abstract: A projection lens system includes, in order from the magnification side, a negative first group G1 and positive second to fifth groups G2 to G5. In the lens system, the first group G1 has aspheric surface, a lens closest to the magnification side (L7) in the fourth group G4 has an aspheric surface, and the fifth group G5 is formed of one positive lens. During zooming, the first group G1 and the fifth group G5 remain stationary, while the second to fourth groups G2 to G4 are moved separately. Furthermore, the lens system satisfies the expression 0.8<d34/fw, where fw denotes a focal length of the whole system at the wide-angle end, and d34 denotes an air space between the third lens group G3 and the fourth lens group G4 at the wide-angle end.

Abstract: A zoom lens system comprising, in order from an object along an optical axis: a first lens group having a negative refractive power; a second lens group having a positive refractive power; and a third lens group having a positive refractive power; the following conditional expression being satisfied: 0.6<Ymax×ft/f12<1.0 where Ymax denotes the maximum image height of the zoom lens system, ft denotes a focal length of the zoom lens system in a telephoto end state, and f1 denotes a focal length of the first lens group.

Abstract: A zoom lens includes a first lens group having negative power, a second lens group having positive power, a third lens group having positive power, and a fourth lens group having positive power, disposed in this order from the enlargement side to form the entire structure. At the time of zooming from the wide angle side to the telephoto side, the first lens group shifts from the enlargement side to the reduction side and the second and third lens groups shift from the reduction side to the enlargement side and the fourth lens group is fixed. The overall length of the zoom lens becomes the maximum at the wide angle end.

Abstract: A zoom lens includes a first and a second lens group respectively having negative and positive refractive power, and changes a focal length by changing a distance between the first and the second lens group. The second lens group includes a first lens having positive refractive power and a convex surface, a second lens having positive refractive power, an aspheric surface, and a convex surface, a third lens having negative refractive power, a fourth lens having positive refractive power, and a fifth lens including one lens or more having positive refractive power. The third and the fourth lenses are connected, and the zoom lens satisfies Nd21>1.8 and ?d24>80, where Nd21 is a refractive index of the first lens of the second lens group at a d-line, and ?d24 is an Abbe number of the fourth lens of the second lens group at a d-line.

Abstract: A three-unit zoom lens system includes in order from an object side thereof a first lens unit G1 having a negative refracting power, a second lens unit G2 having a positive refracting power, a third lens unit G3 having a negative refracting power, and an aperture stop which is at an image side of the first lens unit G1, and at the object side of a lens surface nearest to the image side of the second lens unit G2, and which moves integrally with the second lens unit. At a time of zooming from a wide angle end to a telephoto end, a distance between the first lens unit G1 and the second lens unit G2 is narrowed, and a distance between the second lens unit G2 and the third lens unit G3 changes. The second lens unit G2 moves toward the object side at the time of zooming from the wide angle end to the telephoto end. The third lens unit G3 moves to be positioned at the object side at the telephoto end, with respect to the wide angle end.

Abstract: A three-unit zoom lens includes, in order from the object side, a negative first lens unit G1, a positive second lens unit G2 and a third lens unit G3, wherein during zooming from the wide angle end to the telephoto end the distance between the first lens unit G1 and the second lens unit G2 decreases and the distance between the second lens unit G2 and the third lens unit G3 changes. The first lens unit G1 is composed of one negative lens component including, in order from the object side, a negative lens having a concave surface directed toward the image side and a positive lens having a convex surface directed toward the object side. The second lens unit G2 includes at least one negative lens and a plurality of positive lenses, wherein at least three lenses among these lenses are cemented to adjacent lenses, the total number of lens components included in the second lens unit G2 is two or less. The third lens unit is composed of one lens component composed of two or less lenses.

Abstract: A zoom lens including a first lens group with a negative refractive power and a second lens group with a positive refractive power is provided. The first lens group includes a first lens, a second lens, and a third lens arranged from an object side to an image side in sequence. The refractive powers of the first, second, and third lenses are negative, negative, and positive sequentially. The second lens group includes a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged from the object side to the image side in sequence. The refractive powers of the fourth, fifth, sixth, and seventh lenses are positive, positive, negative, and positive sequentially. The first lens group and the second lens group are capable of moving between the object side and the image side.

Abstract: A zoom lens includes, in order from the object side thereof, a first lens unit G1 having a negative refracting power and a second lens unit G2 having a positive refracting power. During zooming from the wide angle end to the telephoto end, the distance between the first lens unit G1 and the second lens unit G2 decreases. Letting the term “lens component” refer to a lens member whose surfaces that are in contact with air on the optical axis include only two surfaces, one being an object side surface and the other being an image side surface, the first lens unit G1 is comprised of a negative lens component in the form of a cemented lens having a negative refracting power that has, in order from the object side, a negative lens having a concave surface directed toward the image side and a positive lens having a convex surface directed toward the object side, and the second lens unit G2 includes a lens component in the form of a cemented lens having at least one negative lens and a positive lens.

Abstract: An image capturing lens including: in order from an object side, a first lens group having a negative refractive power; a stop; and a second lens group having a positive refractive power; the first lens group including, in order from the object side, a first lens in a meniscus shape having a convex surface which faces the object side and a negative refractive power, and a second lens in a meniscus shape having a convex surface which faces the object side and a positive refractive power, and the second lens group including, in order from the object side, a third lens in a double-convex shape having a positive refractive power, a fourth lens in a double-concave shape having a negative refractive power, and a fifth lens having a positive refractive power.

Abstract: A zoom lens includes, in order from an object side, a first lens group fixed upon zooming and wholly having a negative refractive power, a second lens group formed by an optical-path bending prism fixed upon zooming and, a third lens group allowed to move upon zooming and wholly having a positive refractive power, a fourth lens group allowed to move upon zooming and wholly having a negative refractive power, and a fifth lens group fixed upon zooming and wholly having a positive refractive power. By arranging a zooming group having the positive third and negative fourth lens groups without arranging a positive fixed lens group in back of the prism, the overall length can be easily reduced as compared to the structure arranging a fixed lens group between a prism and a zooming group.

Abstract: A zoom lens includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. When a lens positional state changes from a maximum wide angle state to a maximum telephoto state, the second lens group moves on an optical axis toward an object, and the first and the third lens groups also move in an optical axis direction such that a gap between the first lens group and the second lens group decreases, while gap between the second lens group and the third lens group is increased. When a change in subject position occurs, close-range focusing is performed by movement of the third lens group, and image shift is provided by shifting the second lens group in directions approximately perpendicular to the optical axis.

Abstract: A projection zoom lens is provided and includes: in order from the magnification side, a negative first lens group performing focusing with being fixed during power-varying; a positive second lens group, a positive third lens group, a positive fourth lens group, a positive fifth lens group, which are moved with correlation; and a positive sixth lens group fixed during the power-varying. An aperture diaphragm is moved between the fourth lens group and the fifth lens group during the power-varying to keep Fno constant in the whole power-varying region. In addition, the expression of 1.7<Bf/f<3.0 is satisfied, where f is a focal length of the whole system, and Bf is a back focal length (air conversion distance) of the whole system.

Abstract: A microscope optical system includes, in order from an object side to an image side, a first lens group, a second lens group, a stop, a third lens group, a fourth lens group and a sensor. The first to fourth lens groups all have at least one lens element and at least one of lens elements of the first to fourth lens groups has an aspheric surface. The microscope optical system satisfies several specific conditions so as to provide microscope images of high resolution and high zoom ratio. A digital microscope having the microscope optical system adopts a CCD sensor so that a observer may observe microscope images displayed on a large display screen and store the images for subsequent edition or inspection.

Abstract: A zoom lens system comprising a first lens unit of negative power, a second lens unit of positive power and a third lens unit of positive power, wherein in zooming, the lens units move respectively along an optical axis so that an interval of first lens unit and second lens unit decreases while an interval of second lens unit and third lens unit changes with variable magnification, the first lens unit comprises one object side negative lens element and one image side positive lens element, which have an aspheric surface, and the conditions: n12>1. 88, v12<26 and 5.0<?iW<20.0 (?W>30, n12 and v12 are refractive index and Abbe number, respectively, of the image side positive lens element of the first lens unit, ?i W is an incident angle of the principal ray onto the image sensor at the maximum image height at a wide-angle limit) are satisfied.

Abstract: A three-unit zoom lens system includes in order from an object side thereof, a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, and a third lens unit having a refracting power. The first lens unit includes a biconcave negative lens component nearest to the object side, and the biconcave negative lens component is the only negative lens component in the first lens unit. The second lens unit includes a cemented lens component which includes in order from the object side thereof, at least three lenses cemented mutually on an optical axis, namely a first positive lens, a negative lens, and a second positive lens. A surface on the image side of the negative lens is a concave surface, and the negative lens has an Abbe's number smaller than the Abbe's number for the first positive lens and the second positive lens, and has a refractive index higher than a refractive index of the second positive lens.

Abstract: A zoom lens for forming an optical image of an object on a sensing surface of an image sensor at a variable magnification has first, second, third, fourth and fifth lens groups with positive-negative-positive-negative-positive zoom arrangement. Between the second lens group and the fourth lens group, an optical aperture stop is located. The fourth lens group is composed of one negative lens element having at least one aspherical surface and having a paraxial radius of curvature of an image side surface smaller than a paraxial radius of curvature of an object side surface, and satisfies conditional formula ?1.15<f4/?{square root over (fw·ft)}<?0.5 (where f4 represents a focal length of the fourth lens group, fw represents a focal length of an entire system at a wide-angle end, and ft represents a focal length of the entire system at a telephoto end).

Abstract: A variable-power imaging optical system is provided and includes three, negative, positive and positive lenses. A first group includes a negative lens and a positive lens. A second lens group includes a positive lens, a negative lens and an aberration-correcting lens. A third lens group includes an aberration-correcting lens L6. During zooming, the first and second lens groups are independently moved from each other. During focusing, the first and second lens groups are moved jointly. Ng2>1.6, ?g2<29 and TL/YIM<11.0 are satisfied. (Ng2: refractive index of the second lens L2, ?g2: Abbe number of the second lens L2, TL: maximum lens-system overall length, YIM: image height (a half length of a diagonal line).

Abstract: Disposed in order from a magnification side are a negative first group which is fixed during zooming to effect focusing, second to fifth groups of positive refractive power which move with mutual relationship during magnification variation, and a fixed sixth group. A negative lens made of a glass material which has an anomalous dispersion property and which has 70 or more in Abbe number is disposed in the first lens group. A positive lens made of a glass material which has an anomalous dispersion property and which has 70 or more in Abbe number is disposed in the third group located closer to a reduction side than a diaphragm. The negative lens and the positive lens are cemented to their adjacent lenses, respectively. Also, bf/fw ?2.7 is satisfied where bf denotes a back focus, and fw denotes a focal length of the entire system at a wide-angle end.

Abstract: An optical zoom lens includes, in this order from the object side to the image side thereof, a first lens group of negative refraction power, a second lens group of positive refraction power, and a third lens group of positive refraction power. The optical zoom lens satisfies the formulas of: ?0.45 <Fw/f1<?0.3; and 0.4<f2/|f1|<0.8, where Fw is the smallest effective focal length of the optical zoom lens, f1 is the effective focal length of the first lens group, and f2 is the effective focal length of the second lens group.

Abstract: The zoom lens includes a plurality of lens units. The first lens unit is disposed closest to a magnification side in the plurality of lens units and has a negative optical power, and magnification-varying lens units that are disposed closer to a reduction side than the first lens unit and moves for variation of magnification. The first lens unit includes, in order from the magnification side, a first-A lens sub-unit having a negative optical power and a first-B lens sub-unit having a positive optical power. For focusing from an infinite side to a close side, the first-A and first-B lens sub-units move as a distance therebetween increases, and the first-B lens sub-unit moves toward the reduction side. The zoom lens is capable of correcting well variation of curvature of field due to a projection distance change and has a good optical performance.

Abstract: A zoom lens comprises a plurality of lens units including a first lens unit disposed most adjacent to an enlargement side and having negative refractive power, wherein one or more lens units of the plurality of lens units are moved in the direction of the optical axis thereof during magnification change, and wherein the first lens unit includes a 1-1st lens unit comprising at least one lens of negative refractive power and moved during focusing and a 1-2nd lens unit having positive refractive power, and fixed during focusing.

Abstract: A two-unit zoom lens system includes in order from an object side thereof, a first lens unit G1 having a negative refracting power, a second lens unit G2 having a positive refracting power, and an aperture stop which is disposed between the first lens unit G1 and the second lens unit G2, and which moves integrally with the second lens unit. At a time of zooming from a wide angle end to a telephoto end, a distance between the first lens unit G1 and the second lens unit G2 is narrowed. At the time of zooming from the wide angle end to the telephoto end, the first lens unit G1, after moving toward an image side, moves toward an object side. At the time of zooming from the wide angle end to the telephoto end, the second lens unit G2 moves toward the object side. The second lens unit G2 includes in order from the object side thereof, a front sub-unit having a positive refracting power, and a rear sub-unit having a negative refracting power.

Abstract: An optical system used for an image pickup apparatus including an image pickup element is provided. The optical system includes a negative lens disposed furthest away on the enlargement conjugation side and satisfies the following condition: 80 degrees<2?, where 2? (degrees) denotes an angle of view of the optical system. In addition, the following parameters of the optical system are optimally determined: a lens open angle ? of a surface of the negative lens on the reduction conjugation side, an index of refraction Ndn and an Abbe number vdn of a material of the negative lens for a d-line, and a relative partial dispersion ?gFn of the material of the negative lens for a g-line and an F-line.

Abstract: A projection zoom lens includes, from a screen side to an image source side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power and a fifth lens group having a positive refractive power. Zooming the projection zoom lens from the wide-angle end to the telephoto end causes the second, third and fourth lens groups to move toward the screen side, and the first and fifth lens groups are kept stationary. The projection zoom lens may further include an auto iris being axially movable with the fourth lens group, a composite prism and a cover glass. The projection zoom lens satisfies several conditions so that it can effectively eliminate aberrations and improve the projection image quality.

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: A zoom lens is disclosed. The zoom lens comprises a first lens group located adjacent to an object side and having a negative refractive power, and a second lens group located adjacent to an image side and having a positive refractive power, wherein zooming is made as an interval between the first lens group and the second lens group is varied.

Abstract: To provide a compact, high-performance zoom lens having a small lens aperture for enlarging an image from a light valve such as a DMD for forming an image by changing a reflecting direction of light and projecting the image so enlarged on to a screen or the like, and a zoom lens so provided includes, in order from a magnifying side, a first lens group having a negative refractive power as a whole, a second lens group having a positive refractive power as a whole, and a third lens group having a positive refractive power as a whole, wherein changing the magnification of a whole lens system thereof is attained by configuring such that while a magnification varying operation is in effect, the third lens group is left fixed, the first lens group and the second lens group are made to move on the optical axis.

Abstract: An image projection optical system introduces light from an image-forming element by a zoom lens via an optical element. The optical element satisfies ?(Di×Ndi)/fw>4.0. The zoom lens includes, in order from a magnification side, first and second lens units, and lens units disposed closer to a reduction side than the second lens unit. The first lens unit is a negative lens unit. The lens units disposed closer to the reduction side than the second lens unit satisfy |dn/dt|<1.0×10?5. Magnification-side positive lens elements disposed closer to the magnification side than a negative lens element whose effective diameter is smallest in the lens units disposed closer to the reduction side than the second lens unit satisfy {9.0×?(1/fpA)+5.0×?(1/fpB)+0.5×?(1/fpC)}/?(1/fp)<1. Reduction-side positive lens elements disposed closer to the reduction side than the negative lens element whose effective diameter is smallest satisfy {9.0×?(1/fpA)+0.3×?(1/fpB)+2.0×?(1/fpC)}/?(1/fp)<1.

Abstract: A zoom lens, including: a first group optical system having a negative focal length; a second group optical system having a positive focal length; a third group optical system having a positive focal length, the first group optical system, the second group optical system and the third group optical system being arranged in this order from an object side to an image side; and an aperture stop configured to move together with the second group optical system and disposed on the object side of the second group optical system, a change in magnification being carried out by decreasing a space between the first group optical system and the second group optical system when the change in magnification is carried out from a short focal length end to a long focal length end.

Abstract: At least one exemplary embodiment is directed to a zoom lens including, 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 third lens unit having a positive refractive power. An interval between respective adjacent lens units varies during zooming. The first lens unit includes a composite optical element. The composite optical element includes a lens element and a resin layer having an optical characteristic different from that of the lens element and laid on the lens element. The zoom lens satisfies at least one of predetermined conditions.

Abstract: A variable magnification optical system having at least a first lens group having a negative optical power, a second lens group having a positive optical power, a third lens group having a negative optical power, and a fourth lens element having a positive optical power, in the optical axis direction in zooming, keeps the third lens element immobile with respect to an image surface while moving at least the second lens group and the fourth lens group, whereby: an interval between the first lens group and the second lens group decreases, an interval between the second lens group and the third lens group increases, and an interval between the third lens group and the fourth lens group decreases. Moreover, the variable magnification optical system moves the third lens group in an in-surface direction vertical to the optical axis direction to thereby correct shake resulting from imaging on the image surface, and fulfills predetermined conditional formula.