Abstract: A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

Abstract: A lens system (10) for image pickup includes, in order from an object side (11), a first lens group (G1) with positive refractive power that moves during focusing, a second lens group (G2) with positive refractive power that is disposed on an opposite side of a stop (St) to the first lens group and moves during focusing, and a third lens group (G3) with positive refractive power that is disposed closest to an image plane side (12) and is fixed. The third lens group includes, in order from the object side, a cemented lens (B31) composed of a lens with positive refractive power and a lens with negative refractive power. A combined focal length (f3) of the third lens group and a combined focal length (f12) of the first lens group and the second lens group satisfy a following condition: 2?f3/f12?200.

Abstract: A zoom optical system (ZL) includes: a first lens group (G1) having negative refractive power; a second lens group (G2) having positive refractive power, the second lens group (G2) being disposed further toward an image than the first lens group (G1); and a succeeding lens group (GL) having a vibration-isolating group (GVRb) that moves so as to have a displacement component in a direction orthogonal to an optical axis, the succeeding lens group (GL) being disposed further toward the image than the second lens group (G2), a distance between the first lens group (G1) and the second lens group (G2) changing and a distance between the second lens group (G2) and the succeeding lens group (GL) changing upon zooming, and the following conditional expression being satisfied: 4.899?|f1VRaw/fw|<1000.

Abstract: The objective lens has multiple focal lengths within a focal length interval and a relatively small focal-length ratio in a range from 1.05 to 2.75, and a travel-to-focal-length ratio in a range from 0.05 to 0.4. The objective lens has three main lens groups that define a negative-positive-positive optical system configuration. The first lens group has a rearward lens sub-group that is axially movable for focusing so that the lens length stays the same during focusing. The objective lenses use optical compensation rather than mechanical compensation to move between the design focal lengths each having an in-focus image. This simplifies operation while increasing reliability and reducing cost. A small set of one or more of the objective lenses can be used to replace a large set of prime lenses each having a single focal length, so that fewer lenses are needed to cover the same focal length span.

Abstract: A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

Abstract: A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object and at least one lens component at an image side of the most image side focusing lens group in the focusing lens groups; and predetermined conditional expressions being satisfied, thereby t

Abstract: A three-piece infrared single wavelength projection lens system includes, in order from an image side to an image source side: a first lens element with a positive refractive power; a second lens element with a refractive power; a third lens element with a positive refractive power; a stop disposed before an image source-side surface of the first lens element or between the image source-side surface of the first lens element and an image source-side surface of the second lens element; and the first lens element or the second lens element is made of glass. Such arrangements can provide a three-piece infrared single wavelength projection lens system with better image sensing function.

Abstract: An imaging lens includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens sequentially arranged from a magnifying side to a narrowing side. The second lens and the third lens constitute a first composite lens, the fourth lens and the fifth lens constitute a second composite lens, and the sixth lens and the seventh lens constitute a third composite lens. The imaging lens has the advantages of small size and good imaging quality.

Abstract: Embodiments of the present disclosure relate generally to a projecting status indicator for use in connection with a laboratory machine or instrument (collectively referred to as a “unit”). The indicator projects a projected visible light image or beam of light in a line directly above a particular unit so that lab personnel can tell the status of the unit from a distance. In a specific embodiment, the indicator projects an extended line of light on a ceiling above the unit, rather than a small point of light.

Abstract: The present disclosure discloses an optical imaging lens assembly. The optical imaging lens assembly includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, sequentially arranged from an object side to an image side along an optical axis. The first lens, the second lens, the fifth lens, the seventh lens, and the eighth lens may respectively have a positive focal power or a negative focal power. A combined focal power of the third lens and the fourth lens is a positive focal power. The sixth lens may have a positive focal power. An effective focal length f of the optical imaging lens assembly and a combined focal length f34 of the third lens and the fourth lens satisfy: 0.5?f/f34<1.0.

Abstract: An optical imaging lens may include a first, a second, a third, a fourth, a fifth and a sixth lens elements positioned in an order from an object side to an image side. The optical imaging lens may satisfy (G12+G56)/(G23+T3+G34)?2.500, wherein an air gap between the first lens element and the second lens element along the optical axis is represented by G12, an air gap between the second lens element and the third lens element along the optical axis is represented by G23, an air gap between the third lens element and the fourth lens element along the optical axis is represented by G34, an air gap between the fifth lens element and the sixth lens element along the optical axis is represented by G56, and a thickness of the third lens element along the optical axis is represented by T3.

Abstract: An optical imaging lens including a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element arranged in sequence from an object side to an image side along an optical axis is provided. Each lens element includes an object-side surface and an image-side surface. The first lens element has negative refracting power. The second lens element has negative refracting power, and a periphery region of the object-side surface of the second lens element is convex. An optical axis region of the image-side surface of the fourth lens element is concave. An optical axis region of the image-side surface of the sixth lens element is concave. A periphery region of the image-side surface of the sixth lens element is convex.

Abstract: The zoom lens consists of, in order from the object side, a positive first lens group G1, a negative second lens group G2, a negative third lens group G3, a stop, and a positive fourth lens group G4. During zooming, the first lens group G1 and the fourth lens group G4 remain stationary, and the second lens group G2 and the third lens group G3 move. The first lens group G1 consists of, in order from the object side, a negative first lens group front group G1A that remains stationary during focusing, a positive first lens group intermediate group G1B that moves during focusing, and a positive first lens group rear group G1C that remains stationary during focusing. The following conditional expression relating to an Abbe number ?n1A2 of the second negative lens from the object side is satisfied: 65<?n1A2<110.

Abstract: An imaging optical system consists of, in order from a magnification side: a first imaging optical system that forms an intermediate image on a position conjugate to a magnification side imaging surface; and a second imaging optical system that re-forms the intermediate image on a reduction side imaging surface. The second imaging optical system consists of a plurality of lens groups including at least two movable lens groups which move during zooming. The imaging optical system satisfies predetermined conditional expressions.

Abstract: The present invention includes to a camera optical lens. The camera optical lens includes, in an order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens. The first lens is made of plastic material, the second lens is made of plastic material, the third lens is made of plastic material, the fourth lens is made of plastic material, the fifth lens is made of plastic material, the sixth lens is made of plastic material, and the seventh lens is made of glass material. The camera optical lens satisfies the following conditions: ?10?f1/f??3.1; 1.7?n7?2.2; 1?f6/f7?10; ?10?(R1+R2)/(R1?R2)?10; 0.01?d13/TTL?0.2. The camera optical lens can obtain high imaging performance and a low TTL (Total Track Length).

Abstract: The present disclosure discloses a camera optical lens. The camera optical lens includes, in an order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens. The camera optical lens further satisfies specific conditions.

Abstract: The present invention includes a camera optical lens. The camera optical lens including, in an order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens. The camera optical lens further satisfies specific conditions.

Abstract: The imaging lens consists of, in order from an object side: a first lens group G1; a diaphragm; and a second lens group G2 that has a positive refractive power. The first lens group G1 consists of, in order from the object side, a first A lens group G1A that consists of two negative meniscus lenses concave toward an image side, and a first B lens group G1B that consists of only one positive lens or a negative lens and a positive lens. The second lens group G2 consists of, in order from the object side, a biconvex lens, a biconcave lens, one or two biconvex lenses, and a negative meniscus lens that is concave toward the object side. With such a configuration, the imaging lens satisfies predetermined conditional expressions.

Abstract: A zoom lens includes, in order from object-side, a fixed positive first group including three-or-more lenses, a negative second group including a unit moving toward image-side during zooming toward telephoto-end, a positive third group including a unit moving toward object-side during zooming from wide-end to telephoto-end, a negative fourth group moving during zooming and focusing, and a rear group. Focal lengths of the first group and the zoom lens at wide-end, a movement amount of a unit moving by largest amount during zooming toward telephoto-end in the second group, a largest value of position change between wide-end and telephoto-end of units moving toward an object side during zooming from wide-end to telephoto-end, refractive index for d-line of a positive lens closest to image-side in the first group, and average refractive index for d-line of positive lenses of the first group other than the positive lens are appropriately set.

Abstract: Provided is an optical system including, in order from an object side to an image side, a first lens unit and a second lens unit with a positive refractive power. One of lenses of the first lens unit is the closest to the object side and has a negative refractive power. The second lens unit includes an aperture diaphragm. One of lenses that is included in the second lens unit, located on the object side or the image side of the aperture diaphragm and the closest to the aperture diaphragm has a concave lens surface that faces the aperture diaphragm. Conditions are satisfied whose values are set by using refractive indexes of a negative lens and a positive lens of the first lens unit that respectively have the smallest Abbe number.

Abstract: A projection zoom lens is configured to have an intermediate group that essentially consists of two or three moving lens groups positioned between a first lens group and a final lens group, both of which have positive refractive powers and are fixed while changing magnification. The projection zoom lens changes magnification by moving these moving lens groups. Further, the projection zoom lens satisfies conditional formulas (1) and (2) below: d/fw<1.0??(1), 1.5<fe/fw<7.0??(2), where, d: the distance between the most-reduction-side lens surface of the intermediate group and the most-reduction-side lens surface of the final lens group along the optical axis at the wide angle end, fw: the focal length of the entire system at the wide angle end, and fe: the focal length of the final lens group.

Abstract: An optical image capturing system includes, along the optical axis in order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. At least one lens among the first to the sixth lenses has positive refractive force. The seventh lens can have negative refractive force, wherein both surfaces thereof are aspheric, and at least one surface thereof has an inflection point. The lenses in the optical image capturing system which have refractive power include the first to the seventh lenses. The optical image capturing system can increase aperture value and improve the imagining quality for use in compact cameras.

Abstract: An optical image capturing system includes, along the optical axis in order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. At least one lens among the first to the sixth lenses has positive refractive force. The seventh lens have negative refractive force, wherein both surfaces thereof can be aspheric, and at least one surface thereof has an inflection point. The lenses in the optical image capturing system which have refractive power include the first to the seventh lenses. The optical image capturing system can increase aperture value and improve the imagining quality for use in compact cameras.

Abstract: A projector used a projection lens to enlarge and project image light generated by image generator. When it is assumed that the on-optical-axis position of a lens surface where the maximum of light ray passage ranges (effective diameter) is minimized in the projection lens is a minimum diameter position, a stop is provided on a lens shifted from the minimum diameter position toward the light exiting side. The lens on which the stop is provided is a lens (for example, fourth lens closest to minimum diameter position) that satisfies 0.8?1??2??1, where ?1 represents the light flux diameter on a surface where the on-axis light flux diameter is maximized, and ?2 is the diameter of the stop.

Abstract: A single focal length lens system includes, in order from an object side to an image side, a first lens unit having positive optical power and a second lens unit including a lens element that moves in a direction of an optical axis with respect to an image surface in focusing from an infinity in-focus condition to a close-object in-focus condition. The first lens unit includes an aperture diaphragm and a lens element A located on the object side of the aperture diaphragm. A lens element B having positive optical power and a lens element C having negative optical power are located on the image side of the aperture diaphragm. Abbe numbers of the lens elements A, B, and C to the d-line and partial dispersion ratios of the lens elements A, B, and C for the g-line and the F-line satisfy a predetermined relation.

Abstract: A zoom lens is constituted by, in order from the object side: a negative first lens group; an aperture stop; a positive second lens group; a negative third lens group; and a positive fourth lens group. All of the lens groups move along the optical axis when changing magnification from the wide angle end to the telephoto end such that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group increases. The first lens group is constituted by, in order from the object side, a 1-1 lens having a negative refractive power, a 1-2 lens having a negative refractive power, and a 1-3 lens having a positive refractive power. Conditional Formula (1) below is satisfied. 1.75<ndave<1.

Abstract: A projection system includes a first lens group to an n-th lens group with n being 6 or 7 sequentially arranged from a enlargement side. The first lens group includes a first-first lens group and a first-second lens group sequentially arranged from the enlargement side. The two lens groups are separated from each other by a variable distance for image plane correction. The first lens group and the n-th lens group are fixed and the second lens group to the (n?1)-th group are moved when the magnification is changed. The following conditional expression is satisfied: 2<BF/fw<2.8, where fw represents the focal length of the projection system operating at the wide angle end, and BF represents the air conversion length of the back focal distance of the projection system.

Abstract: A projection zoom lens constituting a projection optical system of a projector, which projects an image displayed on a surface of an image display element on a projected surface, so as to magnify and display the image includes, in order from the projected surface side to the image display element side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group, wherein a refractive power of the fifth lens group is weaker than the refractive power of the first lens group, the refractive power of the second lens group, the refractive power of the third lens group, and the refractive power of the fourth lens group.

Abstract: Disclosed is a projection zoom lens used in an image display device configured to project an image onto a target projection surface and display a magnified image of the image, in which the projection zoom lens has a five-lens-group configuration in which first to fifth lens groups G1 to G5 are arranged from the magnification side toward the reduction side, and each of the constituent lens groups or lenses included in the lens groups has a combination of negative and positive refractive powers, and in the lens configuration, focal lengths of the constituent lens groups, relative travel distances, lens distances to the image display element, and constituent lens shapes are properly selected.

Abstract: A zoom lens including a first lens group and a second lens group is provided. The first lens group having a negative refractive power is disposed between an object side and an image side and includes a first lens having a negative refractive power. The second lens group having a positive refractive power is disposed between the first lens group and the image side and includes a second lens, a third lens, a fourth lens and a fifth lens arranged in sequence from the object side to the image side. Refractive powers of the second lens, the third lens, the fourth lens and the fifth lens are positive, positive, negative and positive in sequence, wherein the first lens has a surface facing the object side, a radius of curvature of the surface is R1, and |R1|>700 mm.

Abstract: An imaging lens consists of, in order from the object side, a negative first lens, a positive second lens, a positive third lens, a negative fourth lens, a positive fifth lens, a positive sixth lens, and a negative seventh lens. When f is the focal length of the entire system, D4 is the air space between the second lens and the third lens, f345 is the combined focal length of the third lens, the fourth lens, and the fifth lens, f1 is the focal length of the first lens, and f2 is the focal length of the second lens, the following conditional formulae are satisfied: D4/f<0.39??(4) 1.8<f345/f??(6) f1/f2<?0.42??(7).

Abstract: A zoom lens system comprising: a negative first lens unit including at least one positive lens element; a positive second lens unit including at least one negative lens element; and subsequent lens units including an aperture diaphragm, wherein the subsequent lens units include a most-image-side lens unit fixed to an image surface in focusing, a first focusing lens unit is provided between the aperture diaphragm and the most-image-side lens unit, and the conditions: 1.0<LSW/{fT×tan(?T)}<2.6 and 0.8<LG1G2/fW<2.8 (LSW: axial distance from aperture diaphragm to image surface at wide-angle limit, fT: focal length of entire system at telephoto limit, ?T: half view angle at telephoto limit, LG1G2; axial distance between most-image-side lens element in first lens unit and most-object-side lens element in second lens unit at wide-angle limit, fW: focal length of entire system at wide-angle limit) are satisfied.

Abstract: A wide field optically athermalized orthoscopic lens system includes, in order from object to image, a first lens having a negative power, a second lens having a positive power, a third lens group having a positive power, a fourth lens having a positive power and a fifth lens having a negative power. The third lens group includes two lenses having, in order, a first lens with positive power and a second lens with negative power. The powers, shapes, Abbe dispersion values and temperature coefficients of refractive indices of the lenses are selected such that the lens system is athermalized, orthoscopic and achromatized over a wide (e.g. >140° C.) temperature range.

Abstract: A projection lens includes a first lens group, a second lens group and a third lens group, all of which are arranged in sequence from an projection side to an image source side along an optical axis. The first lens group is with negative refractive power and includes four lenses. The second lens group is with positive refractive power and includes two lenses. The third lens group is with positive refractive power and includes a stop and six lenses.

Abstract: A zoom lens includes in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. At the time of zooming, distances between the lens units change, and a distance between the first lens unit and the second lens unit at a telephoto end is shorter than a distance between the first lens unit and the second lens unit at a wide angle end, and an aperture stop is disposed on an image side of an image-side surface of the first lens unit, and on an object side of an image-side surface of the second lens unit, and the zoom lens satisfies the conditional expressions.

Abstract: A zoom lens includes: a first lens group having a negative refractive power; and a second lens group having a positive refractive power, provided in this order from an object side. Magnification is changed by moving the first lens group and the second lens group. The first lens group includes a first lens having a negative refractive power, a second lens, a third lens having a negative refractive power, and a fourth lens having a positive refractive power, provided in this order from the object side. The zoom lens satisfies predetermined conditional formulae.

Abstract: A zoom lens includes: a first lens group having a positive refractive power which is fixed while changing magnification; a second lens group constituted by two or more magnification changing groups; an aperture stop; and a third lens group having a positive refractive power which is fixed while changing magnification, provided in this order from an object side. The magnification changing groups respectively move along an optical axis while changing magnification from a wide angle end to a telephoto end. The zoom lens satisfies the following conditional formula: u?/u<0.5??(1) wherein u is the angle of inclination of a paraxial chief ray of light that enters the lens surface most toward the object side within the first lens group, and u? is the angle of inclination of the paraxial chief ray of light that exits the lens surface most toward an image side within the first lens group.

Abstract: A zoom lens and a zoom lens module are provided. The zoom lens is configured to form an image of an object at an object side onto an image plane at an image side. The zoom lens includes a first lens group, a second lens group, a third lens group and a fourth lens group disposed in sequence from the object side towards the image side. The refractive powers of the first lens group, the second lens group, and the third lens group are negative, positive, and negative, respectively. The zoom lens satisfies 1.90<|T1G/FW|<2.40. T1G is a distance of the first lens group along an optical axis of the zoom lens, and FW is an effective focal length of the zoom lens when the zoom lens is at a wide-end.

Abstract: A zoom lens system comprising, in order from an object side: a first lens group G1 having negative refractive power; and a second lens group G2 having positive refractive power, a distance between the first lens group and the second lens group varying upon zooming from a wide-angle end state to a telephoto end state, the first lens group G1 including, in order from the object side, a first lens component having negative refractive power, a second lens component having negative refractive power, a third lens component having positive refractive power, and a fourth lens component having positive refractive power, thereby providing a downsized zoom lens system having excellent optical performance, an optical apparatus equipped therewith and a method for manufacturing the zoom lens system.

Abstract: A zoom lens includes a front group, an aperture stop, and a rear group. The front group includes a lens unit configured not to move during zooming and a front variable power lens unit including one or more lens units and configured not to move during zooming. The rear group includes, in order from a magnification conjugate side to a reduction conjugate side, a rear variable power lens unit having one or more lens units and configured to move during zooming, and a lens unit configured not to move during zooming. The aperture stop moves during zooming, and the front group has an auxiliary stop which moves during zooming. A length from a focal point position of the front group to the aperture stop, and imaging magnifications of the rear group, at a wide angle end and a telephoto end, are set to adequate values.

Abstract: A zoom lens includes: a first lens group having a negative power; and a second lens group having a refractive power, in this order from an object side. The zoom lens satisfies the following conditional formulae: 1.0<D2g/D1g<1.6, 0.08<D2t/ft<0.19, 1.15?ft/|f1|<1.8, and 1.1<ft/f2<1.9, wherein D1g is the distance from a most object side lens surface to a most image side lens surface within the first group, D2g and D2t are the distance from a most object side lens surface to a most image side lens surface within the second group and the distance between an object side partial second lens group and an image side partial second lens group when focused on infinity at a telephoto end, respectively, ft is the focal length of the entire system at the telephoto end, and f1 and f2 are the focal lengths of the first group and the second group, respectively.

Abstract: A zoom lens includes: a first lens group having a negative refractive power; and a second lens group having a positive refractive power, provided in this order from an object side. Magnification is changed by moving the first lens group and the second lens group. The first lens group includes a first lens having a negative refractive power, a second lens, a third lens having a negative refractive power, and a fourth lens having a positive refractive power, provided in this order from the object side. The zoom lens satisfies predetermined conditional formulae.

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

Abstract: A variable magnification optical system for projection consists of a negative lens group and a positive lens group in this order from a magnification side. A distance on an optical axis between the negative lens group and the positive lens group changes during magnification change, and an entire system substantially consists of six lenses. The negative lens group consists of a first lens including an aspheric surface and a second lens that is a negative single lens in this order from the magnification side.

Abstract: A projector for projecting light onto a projection surface includes a first group (1) with a negative meniscus, a second group (2) with positive refractive power, a third group (3) with a single lens, a fourth group (4) with a lens with positive refractive power, and a field lens (5) with positive refractive power, such that the light passes through the projection objective from the fourth to the first group. In order to be provide a high image quality with a small number of optical components and the smallest dimensions, the projector is configured so the common focal width of the fourth group (4) and the field lens (5) is smaller than twice the image circle diameter (9) of the projection objective and the maximum free diameter (8) is smaller than the overall focal width, and in particular smaller than 0.8 times the overall focal width of the projection objective.

Abstract: A zoom lens includes, in order from an object side to an image side, first to fourth lens units having negative, positive, negative, and positive refractive power, respectively. Each lens unit moves during zooming so that a distance between the first lens unit and the second lens unit at the telephoto end is shorter than at the wide-angle end and a distance between the second lens unit and the third lens unit and a distance between the third lens unit and the fourth lens unit at the telephoto end are larger than those at the wide-angle end. A focal length of the third and fourth lens units, a focal length of the entire zoom lens at the wide-angle end, a focal length of the entire zoom lens at the telephoto end, and a sum of axial thicknesses of the first to fourth lens units are appropriately set.

Abstract: An aperture stop is arranged on the reduction side of the most reduction-side lens element in a fourth group; during zooming from the tele-end to the wide-end through a middle position that fulfills conditional formula 0.99<fm/(ft×fw)½<1.01, first and fifth groups remain stationary, the composite power of third and fourth groups is constantly positive, and the third and fourth groups move from the enlargement side to the reduction side, satisfying conditional formulae: 7<?TM3/|?TM2|, 7<?TW3/|?TW2|, 7<?TM4/|?TM2|, 7<?TW4/|?TW2|, 0.9<?TM4/?TM3<1.1, 0.9<?TW4/?TW<1.1 (ft, fm, and fw are the entire-system focal lengths at the tele-end, the middle position, and the wide-end; ?TM2-4 are the movement amounts of the second to fourth groups from the tele-end to the middle position; and ?TW2-4 are the movement amounts of the second to fourth groups from the tele-end to the wide-end).

Abstract: A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The lens groups that are moved during magnification change substantially consist of three lens groups, wherein the most enlargement-side lens group is a negative lens group. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the last lens group, and a focal length of the first lens group are satisfied.

Abstract: A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The most enlargement-side lens group (the second lens group) of the lens groups that are moved during magnification change has a negative refractive power. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the second lens group and a focal length of the last lens group are satisfied.

Abstract: The zoom lens includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a rear unit including one or more lens units, a distance between every adjacent lens units varies during zooming, and an aperture diaphragm on the image side of the first lens unit, a combined focal length of the rear unit at a wide-angle end being positive. One lens unit LG on the object side of the aperture diaphragm is made of a solid material, and includes an optical element GnNL having a negative refractive power and another optical element having a positive refractive power, and the predetermined conditions are satisfied.