Abstract: A compact and lightweight zoom lens system having excellent imaging performance, which is favorably applicable to an interchangeable-lens type digital camera system, is provided. The zoom lens system of the present invention includes, in order from an object side to an image side, a first lens unit having positive optical power and composed of not more than two lens elements, a second lens unit having negative optical power, a third lens unit having negative optical power, and a fourth lens unit having positive optical power. In zooming from a wide-angle limit to a telephoto limit, the fourth lens unit moves along an optical axis. Further, the following condition (9) and (10) are satisfied: 1.50<nd1<1.72, 50<vd1<75 (nd1: a refractive index to the d line of a positive lens element constituting the first lens unit, vd1: an Abbe number of a positive lens element constituting the first lens unit).

Abstract: A compact and lightweight zoom lens system having excellent imaging performance, which is favorably applicable to an interchangeable-lens type digital camera system, is provided. The zoom lens system of the present invention includes, a first lens unit having positive optical power and arranged closest to an object side, a focusing lens unit that moves along an optical axis from an infinity in-focus condition to a close-object in-focus condition, an image blur compensation sub-lens unit that includes at least one lens element and that moves in a direction perpendicular to the optical axis, and an aperture diaphragm arranged on an image side relative to the focusing lens unit and the image blur compensation sub-lens unit. The focusing lens unit, the image blur compensation sub-lens unit, and the aperture diaphragm are adjacent with one another. Further, the following condition (8) is satisfied: 0.7<BFW/fW<3.

Abstract: A compact and lightweight zoom lens system having excellent imaging performance, which is favorably applicable to an interchangeable-lens type digital camera system, is provided. The zoom lens system of the present invention includes, in order from an object side to an image side, a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having negative optical power, a fourth lens unit having positive optical power and including at least one resin lens, and an aperture diaphragm arranged in the fourth lens unit. In zooming from a wide-angle limit to a telephoto limit, an interval between the third lens unit and the fourth lens unit monotonically decreases. Further, the following condition (1) is satisfied: 1.0<T4/fW<3.5 (T4: a thickness of the fourth lens unit in an optical axis direction, fW: a focal length of the entire system at a wide-angle limit).

Abstract: Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system, in order from an object side to an image side, includes a first lens unit G1 having positive optical power, a second lens unit G2 having negative optical power, a third lens unit G3 having negative optical power and including an aspherical surface, and a fourth lens unit G4. The second lens unit G2 includes at least a lens element having a negative optical power and a lens element having a positive optical power. At the time of zooming, the third lens unit G3 moves in a direction along the optical axis such that an interval between the second lens unit G2 and the third lens unit G3 is made longer at a telephoto limit than the interval at a wide-angle limit.

Abstract: A zoom lens system includes a first unit having a positive refractive power, a second unit having a negative refractive power that moves for magnification-varying, a third unit having one of a positive refractive power and a negative refractive power that moves for magnification-varying, and a fourth unit having a positive refractive power.

Abstract: A zoom lens system having a high zoom ratio and excellently correcting various aberrations over an entire zoom range between a wide angle end and a telephoto end to obtain high optical performance in the entire zoom range, includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit, and a fourth lens unit. The fourth lens unit includes a front subunit and a rear subunit, the rear subunit being constituted by two negative lenses and at least three positive lenses. The rear subunit includes a first rear-subunit and a second rear-subunit. Each of the first rear-subunit and the second rear-subunit includes a negative lens and at least one positive lens. Lens materials are suitably set for the first rear-subunit and the rear second-subunit.

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

Abstract: Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system of the present invention, in order from an object side to an image side, includes a first lens unit G1 having positive optical power, a second lens unit G2 having negative optical power, a third lens unit G3 having negative optical power, and a fourth lens unit G4 having positive optical power. At the time of zooming, all lens units moves in a direction along the optical axis such that intervals among respective lens units varies. Further, at the time of zooming, the third lens unit G3 moves in the direction along the optical axis such that the interval between the second lens unit G2 and the third lens unit G3 is made longer at a telephoto limit than the interval at a wide-angle limit. Still further, condition (6): ?1.6<fF/f4?<?0.

Abstract: Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system of the present invention, in order from an object side to an image side, includes a first lens unit G1 having positive optical power, a second lens unit G2 having negative optical power, a third lens unit G3 having negative optical power, and a fourth lens unit G4 having positive optical power. At the time of zooming, at least the first lens unit G1 moves from a wide-angle limit to a telephoto limit. The fourth lens unit G4 includes a first sub lens unit having positive optical power and a second sub lens unit having negative optical power, the second sub lens unit being arranged at the image side relative to the first sub lens unit.

Abstract: A zoom lens, including: a first lens unit and a second lens unit, in which the first lens unit includes: a first lens sub unit which does not move; a second lens sub unit which moves for focusing; and a third lens sub unit which does not move; and in which the following expression is satisfied, ?2.27×10?3<(?p??na)/(?p??na)<?1.9×10?3, where ?na and ?na represent an average value of an Abbe number ? and an average value of a partial dispersion ratio ? of negative lenses included in the first lens sub unit, respectively, ?p and ?p represent an Abbe number and a partial dispersion ratio of a positive lens having a smallest Abbe number among lenses constituting the first lens sub unit, respectively, ?=(Ng?NF)/(NF?NC), and Ng, NF and NC denote refractive indexes at the g-line, the F-line and a C-line, respectively.

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

Abstract: A zoom lens system is provided that includes a compactly constructed focusing lens unit and that has a suppressed change in the image magnification at the time of movement of a focusing lens unit. The zoom lens system according to the present invention comprises: a positive lens unit that is arranged on an object side relative to the aperture diaphragm; a negative lens unit that is arranged on an image side relative to the positive lens unit and on an object side relative to the aperture diaphragm; and a focusing lens unit that is arranged in an optical path between the negative lens unit and the aperture diaphragm. The zoom lens system satisfies the condition (4): 1.20<?NT/?NW<4.50 (here, fT/fW>3.

Abstract: A zoom lens system includes, in order of from an object side to an image side: a first lens unit which does not move for zooming; a second lens unit moving during zooming; a third lens unit moving during zooming; and a fourth lens unit which does not move for zooming. The first lens unit includes a negative lens, a positive lens, a positive lens, and a positive lens, and when an Abbe number ? and a partial dispersion ratio ? of a material of the negative lens are denoted respectively by ?n and ?n, an average value of Abbe numbers ? and an average value of partial dispersion ratios ? of materials of the positive lenses are denoted respectively by ?pa and ?pa, and a refractive power of the negative lens is denoted by ?n, the following expressions are satisfied: ?1.75×10?3<(?pa??n)/(?pa??n); and 9.1×10?3(1/mm)<|?n|.

Abstract: A zoom lens according to the present invention includes, in order from the object side to the image side, a first lens unit having a positive refracting power, a second lens unit having a negative refracting power, a third lens unit having a negative refracting power, and a fourth lens unit having a positive refracting power, wherein during zooming from the wide angle end to the telephoto end, the first lens unit, the second lens unit, the third lens unit, and the fourth lens unit move in such a way that they are located closer the object side at the telephoto end than at the wide angle end, the distance between the first lens unit and the second lens unit is larger at the telephoto end than at the wide angle end, the distance between the second lens unit and the third lens unit is larger at the telephoto end than at the wide angle end, and the distance between the third lens unit and the fourth lens unit is smaller at the telephoto end than at the wide angle end.

Abstract: A first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having the negative refractive power, and a fourth lens group having the positive refractive power are included in order from an object side, and variation of magnification from a wide-angle end to a telephoto end is performed by monotonically moving the second lens group toward an image side and compensation of a fluctuation of an image surface resulting from the variation of magnification is performed by moving the third lens group. At least one positive lens having an optical material satisfying a conditional expressions is included in at least one of the first lens group G1 and the fourth lens group.

Abstract: A zoom lens system includes, in order of from an object side to an image side: a first lens unit which does not move for zooming; a second lens unit moving during zooming; a third lens unit moving during zooming; and a fourth lens unit which does not move for zooming. The first lens unit includes a negative lens, a positive lens, a positive lens, and a positive lens, and when an Abbe number ? and a partial dispersion ratio ? of a material of the negative lens are denoted respectively by ?n and ?n, an average value of Abbe numbers ? and an average value of partial dispersion ratios ? of materials of the positive lenses are denoted respectively by ?pa and ?pa, and a refractive power of the negative lens is denoted by ?n, the following expressions are satisfied: ?1.75×10?3<(?pa??n)/(?pa??n); and 9.1×10?3(1/mm)<|?n|.

Abstract: A zoom lens including in order from an object side to an image side: a positive first lens unit which does not move for zooming; a negative second lens unit for magnification, and a rear lens group including two or more lens units, in which: the first lens unit includes a first subunit not moving for focusing and a second subunit moving for focusing, and the first subunit includes two or more negative lenses and one or more positive lenses; and an average Abbe number and an average partial dispersion ratio of materials of the negative lenses included in the first subunit, average Abbe number and average partial dispersion ratio of materials of the one or more positive lenses included in the first lens unit, combined focal length of the negative lenses included in the first subunit, and focal length of the zoom lens at telephoto end are appropriately set.

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

Abstract: A zoom lens system including, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a negative refractive power; an aperture stop; and a fourth lens unit having a positive refractive power and including a front lens subunit and a rear lens subunit in which Abbe numbers of lenses in the rear lens subunit satisfy the following expression, 0.400<?m/(?rp??rn)<0.630, where ?m represents the Abbe number of the material of a first positive lens having the largest dispersion of the positive lenses included in the rear lens subunit, ?rp represents the average Abbe number of materials of positive lenses other than the first positive lens in the rear lens subunit, and ?rn represents the average Abbe number of materials of negative lenses in the rear lens subunit.

Abstract: A zoom lens is provided and includes: in order from an object side thereof, a first group having a positive refractive power; a second group having a negative refractive power; a stop; a third group having a negative refractive power, the third group including at least two positive lenses and at least two negative lenses; and a fourth group having a positive refractive power. Power variation from a wide angle end to a telephoto end of the zoom lens is performed by moving the second group to an image side along an optical axis thereof, while the first group and the third group are fixed, and correction of an image plane caused by the power variation and focusing is performed by moving the fourth group along the optical axis.

Abstract: A zoom lens system including, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a negative refractive power; an aperture stop; and a fourth lens unit having a positive refractive power and including a front lens subunit and a rear lens subunit in which Abbe numbers of lenses in the rear lens subunit satisfy the following expression, 0.400<?m/(?rp??rn)<0.630, where ?m represents the Abbe number of the material of a first positive lens having the largest dispersion of the positive lenses included in the rear lens subunit, ?rp represents the average Abbe number of materials of positive lenses other than the first positive lens in the rear lens subunit, and ?rn represents the average Abbe number of materials of negative lenses in the rear lens subunit.

Abstract: Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system of the present invention, in order from an object side to an image side, includes a first lens unit G1 having positive optical power, a second lens unit G2 having negative optical power, a third lens unit G3 having negative optical power, and a fourth lens unit G4 having positive optical power. At the time of zooming, all lens units moves in a direction along the optical axis such that intervals among respective lens units varies. Further, at the time of zooming, the third lens unit G3 moves in the direction along the optical axis such that the interval between the second lens unit G2 and the third lens unit G3 is made longer at a telephoto limit than the interval at a wide-angle limit. Still further, condition (6): ?1.6<fF/f4?<?0.

Abstract: Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system of the present invention, in order from an object side to an image side, includes a first lens unit G1 having positive optical power, a second lens unit G2 having negative optical power, a third lens unit G3 having negative optical power, and a fourth lens unit G4 having positive optical power. At the time of zooming, at least the first lens unit G1 moves from a wide-angle limit to a telephoto limit. The fourth lens unit G4 includes a first sub lens unit having positive optical power and a second sub lens unit having negative optical power, the second sub lens unit being arranged at the image side relative to the first sub lens unit.

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

Abstract: A zoom lens includes, from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and including a reflective member configured to fold an optical path, a third lens unit having a negative refractive power, an aperture stop, and a rear lens unit having a positive refractive power as a whole and including at least one lens unit. During zooming, the second lens unit does not move and the distances between the adjacent lens units change.

Abstract: A first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having the negative refractive power, and a fourth lens group having the positive refractive power are included in order from an object side, and variation of magnification from a wide-angle end to a telephoto end is performed by monotonically moving the second lens group toward an image side and compensation of a fluctuation of an image surface resulting from the variation of magnification is performed by moving the third lens group. At least one positive lens having an optical material satisfying a conditional expressions is included in at least one of the first lens group G1 and the fourth lens group.

Abstract: A zoom lens has, in order from the object side to the image side, a first lens unit that does not move during zooming and has positive refractive power, a second lens unit that performs zooming and has negative refractive power, a third lens unit that corrects image plane variation caused by zooming and has negative refractive power, and a fourth lens unit that does not move during zooming and has positive refractive power. The first lens unit has, in order from the object side to the image side, a first lens subunit that does not move during focusing and has negative refractive power, a second lens subunit that is configured to move along the optical axis during focusing and has positive refractive power, a third lens subunit that does not move during focusing and has positive refractive power. The second lens subunit has at least one aspherical lens surface AS12.

Abstract: A zoom lens system comprising a plurality of lens units each composed of at least one lens element, wherein an interval between at least any two lens units is changed so that an optical image is formed with a continuously variable magnification, the zoom lens system comprises a first lens unit having positive power, a second lens unit that includes a lens element having a reflecting surface and has negative power and subsequent lens units including at least one lens unit having positive power, and the condition: 0.50<(C?S)/H<1.00(C=?{square root over ( )}(2R·dR?dR2), S is a sag of the image side surface of the most object side lens element in the second lens unit at height H, H is one-half of an optical axial thickness of the lens element having a reflecting surface, R is a radius of curvature of the image side surface, and dR is an interval between the most object side lens element and the lens element having a reflecting surface) is satisfied.

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

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

Abstract: A zoom lens is provided and includes: in order from an object side thereof, a first group having a positive refractive power; a second group having a negative refractive power; a stop; a third group having a negative refractive power, the third group including at least two positive lenses and at least two negative lenses; and a fourth group having a positive refractive power. Power variation from a wide angle end to a telephoto end of the zoom lens is performed by moving the second group to an image side along an optical axis thereof, while the first group and the third group are fixed, and correction of an image plane caused by the power variation and focusing is performed by moving the fourth group along the optical axis.

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

Abstract: A zoom lens includes, in order from object to image sides, first and second lens units having positive and negative refractive power, respectively, and a rear lens group including at least one lens unit having positive refractive power. The rear lens group includes a lens unit IS having negative refractive power and movable in a direction having a component perpendicular to an optical axis so as to displace an imaging position, and a lens unit R_IS having positive refractive power and arranged on the image side of the lens unit IS. The distance between the lens units IS and R_IS is varied during zooming. The following conditions are satisfied: 0.05<|fIS/fT|<0.18 2.0<f1/fR—IS<4.5 where fIS, fT, f1, and fR_IS are focal lengths of the lens unit IS, entire zoom lens at a telephoto end, first lens unit, and lens unit R_IS, respectively.

Abstract: A zoom lens includes, from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and including a reflective member configured to fold an optical path, a third lens unit having a negative refractive power, an aperture stop, and a rear lens unit having a positive refractive power as a whole and including at least one lens unit. During zooming, the second lens unit does not move and the distances between the adjacent lens units change.

Abstract: To provide a high performance compact zoom lens with a small lens aperture which projects an image from a light valve such as a DMD (Digital Micromirror Device) in which an image is formed by changing reflecting directions of light on to a screen or the like in an enlarged fashion, according to the invention, there is provided zoom lens comprising, in order from a magnifying side thereof, a first lens group having a positive or negative refractive power as a whole, a second lens group having a negative refractive power as a whole, a third lens group having a positive or negative refractive power as a whole and a fourth lens group having a positive refractive power as a whole, wherein changing the magnification of the whole lens system thereof is attained by configuring such that the first lens group is left fixed while a magnification varying operation is effect, the second lens group, the third lens group and the fourth lens group are made to move on an optical axis.

Abstract: A zoom lens has, in order from the object side to the image side, a first lens unit that does not move during zooming and has positive refractive power, a second lens unit that performs zooming and has negative refractive power, a third lens unit that corrects image plane variation caused by zooming and has negative refractive power, and a fourth lens unit that does not move during zooming and has positive refractive power. The first lens unit has, in order from the object side to the image side, a first lens subunit that does not move during focusing and has negative refractive power, a second lens subunit that is configured to move along the optical axis during focusing and has positive refractive power, a third lens subunit that does not move during focusing and has positive refractive power. The second lens subunit has at least one aspherical lens surface AS12.

Abstract: A zoom lens includes in the order from an object a first lens group having a negative refractive power, including at least one negative lens and one positive lens, wherein a negative plastic lens having one or more aspherical surfaces is arranged on a side closest to the object; a second lens group having positive refractive power, including a first positive lens, a second positive lens and a negative lens in the order from the object; and a third lens group, wherein each lens group is moved in a direction of an optical axis for zooming, and the following expressions are satisfied: 2.0<|f1/fw|<3.0 1.2<|f1a/fw|<1.8 where f1, f1a and fw represent focal lengths of the first lens group, of the negative plastic lens arranged closest to the object, and at a wide-angle end of an entire zoom lens, respectively.

Abstract: An image pickup apparatus includes a zoom lens including at least two movable lens groups; an image pickup element that converts an optical image formed with the zoom lens into an electric signal; and an image processor that electrically corrects a lateral chromatic aberration to be generated at the zoom lens. The zoom lens satisfies Conditional Expressions (1) and (2) as follows, ?5.0<W_ate(X)/T_ate(X)<?0.2??(1) 0.003<|Max_ate(10)/Himg |<0.03??(2) where W_ate(X) is an aberration amount of the lateral chromatic aberration from the C-line to the g-line, at a wide-angle end, corresponding to a (X×10) % image height, T_ate(X) is an aberration amount of the lateral chromatic aberration from the C-line to the g-line, at a telephoto end, corresponding to a (X×10) % image height, Max_ate(X) is one of W_ate(10) and T_ate(10), the one having a larger absolute value, and Himg is a diagonal length of the image pickup element.

Abstract: An image pickup apparatus includes an image pickup element and an optical system configured to form an image on the image pickup element. The optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and including a reflecting member configured to deflect an optical axis, and a rear lens unit having a positive refractive power and including at least one lens unit having a positive refractive power. The second lens unit is stationary for zooming. During zooming, the image pickup element moves, and an interval between the first lens unit and the second lens unit and an interval between the second lens unit and the rear lens unit vary.

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

Abstract: A first lens group (G1) fixed with respect to the image plane includes a lens (11) having a negative refractive power, a lens (12) having a positive refractive power and a lens (13) having a positive refractive power. A second lens group (G2) has a negative refractive power as a whole, and causes a zooming action when moved along the optical axis. An aperture stop is fixed with respect to the image plane. A third lens group (G3) includes a lens (31) having a negative refractive power and a lens (32) having a positive refractive power, has a positive or negative refractive power as a whole, and is fixed with respect to the direction of the optical axis when zooming and when focusing. A fourth lens group (G4) has a positive refractive power as a whole, and moves along the optical axis such that the image plane, which is displaced by a movement of the second lens group (G2) along the optical axis and by a movement of the object, is maintained at a constant position with respect to a reference plane.

Abstract: A zoom lens system capable of correcting a secondary spectrum is disclosed. The zoom lens system includes a first lens unit with a positive optical power, a second lens unit with a negative optical power, an aperture stop, and a rear lens component including at least one lens unit in an order from an object side to an image side. In the zoom lens system, during zooming from a wide angle end to a telephoto end, an interval between the first lens unit and the second lens unit increases, and an interval between the second lens unit and the aperture stop decreases. Then, a material satisfying the following conditions: ?d1n<35 ?gF1n <?0.0027?d1n+0.680 is used for the negative lens in the first lens unit. Herein, ?d1n represents an Abbe number, and ?gF1n represents a partial dispersion ratio.

Abstract: A zoom lens includes first to fourth lens units arranged in order from an object, respectively. The first lens unit is fixed during power-varying and has positive optical power. The second lens unit is movable during power-varying. The third lens unit is movable so as to compensate image-plane fluctuation in accordance with the power-varying. The fourth lens unit is fixed during the power-varying and has positive optical power. The first lens unit includes a first lens subunit having positive optical power, and a second lens subunit having negative optical power, arranged in order from the object, respectively. One of the first and second lens subunits moves upon focus adjustment. Further, the following conditions are satisfied: ?2.5<f1b/f1a<?0.6 and 0.2<f1/fT<0.8. Wherein f1, f1a, f1b, and fT respectively represent the focal lengths of the first lens unit, the first lens subunit, the second lens subunit, and the overall system of the zoom lens at its telephoto end.

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

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

Abstract: A zoom lens includes, 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 arranged to move during variation of magnification, a third lens unit arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has a first lens subunit of negative refractive power, and an image is displaced by moving the first lens subunit in such a way as to have a component perpendicular to an optical axis of the zoom lens.

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

Abstract: The zoom lens has, in order from the object to image sides, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power, wherein the second lens unit and the fourth lens unit move during zooming. The following condition is satisfied: ?23<20.0, N23>1.9, ?1.0<f2/f2t<?0.05, where f2 represents a focal length of the second lens unit, ft represents a focal length of the entire system at a telephoto end zoom position, and ?23 and N23 represent an Abbe number and a refractive index of the material forming the third lens of the second lens unit, respectively.

Abstract: A compact, ultra-light and high-performance projection optics lens assembly using Diffractive Optics Technology, plastic and glass optics, and Aspheric optics has been designed with only four elements. The lens may be included as is, or scaled to be included in all instruments using conventional Double-Gauss lens forms. The preferred lens is only 20 mm in diameter and 15 mm long has a weight of only 8 g. Thus, two lenses for head mounted stereo displays is only 16 g. Such a stereo display, known as a head-mounted projective display (HMPD), consists of a pair of miniature projection lenses, beam splitters, and miniature displays mounted on the helmet, and retro-reflective sheeting materials placed strategically in the environment.

Abstract: A zoom lens having only four lens groups is disclosed. In order from the object side, these are: a first lens group having positive refractive power, a second lens group having negative refractive power that moves for zooming, a third lens group having negative refractive power that moves for correcting a shift in the image surface position when zooming, and a fourth lens group having positive refractive power and formed of front and rear subgroups, with the rear subgroup consisting of a single positive lens element that moves to correct for different back focus lengths that are required when the zoom lens is used in different television cameras. Various conditions are preferably satisfied in order to maintain favorable correction of spherical aberration and astigmatism even when the back focus of the zoom lens is adjusted slightly so as to compensate for manufacturing tolerances.