Abstract: A zoom lens for projection includes a negative first lens group, a positive second lens group, a positive third lens group, and a positive fourth lens group, which are arranged from the magnification side of the zoom lens in the order mentioned above. The first lens group and the fourth lens group are fixed during zooming, but the second lens group and the third lens group move on optical axis Z of the zoom lens toward the magnification side, based on an operation for operating the zoom lens from wide end to tele end, in such a manner that a distance between the second lens group and the third lens group changes. Further, the following formula (1) is satisfied: 17<FG3/fw??(1), where FG3: focal length of the third lens group, and fw: focal length of entire system at wide end.

Abstract: A wide-angle projection zoom lens includes, in order from the magnification side: a first group that remains stationary during zooming and has a negative refractive power; second to fourth groups that are movable independently from each other during zooming; a fifth group that remains stationary during zooming and has a positive refractive power. The projection zoom lens is configured to be telecentric on the reduction side. The first group includes five lenses having negative, negative, negative, positive, negative refractive powers. During zooming from the wide-angle end to the telephoto end, the first group and the fifth group remain stationary, and the second to fourth groups are movable in a direction of the optical axis so as to narrow a space between the first group and the second group and widen a space between the fourth group and the fifth group.

Abstract: A wide-angle projection zoom lens includes: a first negative lens group for focus adjustment that is fixed when power varies; a second positive lens group, a third negative lens group, and a fourth positive lens group that are moved when power varies; and a fifth positive lens group that is fixed when power varies. The first to fifth lens groups are arranged in this order from a magnification side. The first lens group includes a first negative lens, which is an aspheric lens made of plastic, a second negative lens, a third negative lens, and a fourth positive lens which are arranged in this order from the magnification side. The wide-angle projection zoom lens is configured so as to satisfy four predetermined conditional expressions.

Abstract: A zoom lens for projection includes a negative first lens group, a positive second lens group, a positive third lens group, and a positive fourth lens group, which are arranged from the magnification side of the zoom lens in the order mentioned above. The first lens group and the fourth lens group are fixed during zooming, but the second lens group and the third lens group move on optical axis Z of the zoom lens toward the magnification side, based on an operation for operating the zoom lens from wide end to tele end, in such a manner that a distance between the second lens group and the third lens group changes. Further, the following formula (1) is satisfied: 17<FG3/fw??(1), where FG3 focal length of the third lens group, and fw: focal length of entire system at wide end.

Abstract: A small projection lens includes a first lens, which is a biconvex lens, an aperture, an aperture diaphragm (or an aperture), a second lens, which is a negative meniscus lens having a concave surface facing a magnification side, a third lens, which is a positive meniscus lens having a convex surface facing a reduction side, and a fourth lens, which is a biconvex lens having aspheric surfaces at both sides on an optical axis, arranged in this order from the magnification side. A minimum portion of the length of all lens elements of the small projection lens in a diametric direction vertical to the optical axis is equal to or less than 15 mm, and the small projection lens satisfies the following conditional expression: 2.5<?/S<10.0 (where S indicates the maximum length of a magnification-side image (inch) and ? indicates a magnifying power).

Abstract: A wide-angle projection zoom lens includes: a first negative lens group for focus adjustment that is fixed when power varies; a second positive lens group, a third negative lens group, and a fourth positive lens group that are moved when power varies; and a fifth positive lens group that is fixed when power varies. The first to fifth lens groups are arranged in this order from a magnification side. The first lens group includes a first negative lens, which is an aspheric lens made of plastic, a second negative lens, a third negative lens, and a fourth positive lens which are arranged in this order from the magnification side. The wide-angle projection zoom lens is configured so as to satisfy four predetermined conditional expressions.

Abstract: A wide-angle projection zoom lens includes, in order from the magnification side: a first group that remains stationary during zooming and has a negative refractive power; second to fourth groups that are movable independently from each other during zooming; a fifth group that remains stationary during zooming and has a positive refractive power. The projection zoom lens is configured to be telecentric on the reduction side. The first group includes five lenses having negative, negative, negative, positive, negative refractive powers. During zooming from the wide-angle end to the telephoto end, the first group and the fifth group remain stationary, and the second to fourth groups are movable in a direction of the optical axis so as to narrow a space between the first group and the second group and widen a space between the fourth group and the fifth group.

Abstract: A small projection lens includes a first lens, which is a biconvex lens, an aperture, an aperture diaphragm (or an aperture), a second lens, which is a negative meniscus lens having a concave surface facing a magnification side, a third lens, which is a positive meniscus lens having a convex surface facing a reduction side, and a fourth lens, which is a biconvex lens having aspheric surfaces at both sides on an optical axis, arranged in this order from the magnification side. A minimum portion of the length of all lens elements of the small projection lens in a diametric direction vertical to the optical axis is equal to or less than 15 mm, and the small projection lens satisfies the following conditional expression: 2.5<?/S<10.0 (where S indicates the maximum length of a magnification-side image (inch) and ? indicates a magnifying power).

Abstract: A transparent member having refractive power as a result of curved surface thereon is used in one or more light paths of a three-color projection device in order to correct for the lateral color aberration of the projection lens. The transparent member is positioned between one or more optical modulation element(s) and the beam combining prism of a prism optical system, or alternatively, is on or affixed to the beam combining prism surface. When correcting an image that is enlarged by the projection lens, the curved surface of the transparent member should be convex and positioned on the side of the transparent member nearest the display panels. The focal length of a correction lens that optimally corrects the lateral color of the projection lens depends on the maximum image height at the image input display panel, the lateral color aberration generated by the projection lens, and the air conversion length from the image input display panel to the on axis position of the curved surface.

Abstract: First, second, third, and fourth set lenses are located in this order from the direction of a screen. The first lens group comprises a plastic lens having a weak refracting power and at least one aspherical surface. The second lens group comprises a plastic lens having a weak refracting power and at least one aspherical surface, and an achromatic lens system having a substantial effect on the refracting power of the whole projecting lens. The achromatic lens system is composed of three or four glass lenses, and a plastic lens having a positive refracting power and at least one aspherical surface. The third lens group comprises a plastic lens having a weak refracting power and at least one aspherical surface. The fourth lens group comprises a plastic lens having at least one aspherical surface, and a field flattener lens, which is located with its concave surface facing the screen and which constitutes a liquid optical coupler.

Abstract: A mechanical compensation type zoom lens system capable of improving performances of large diameter lenses, wide angle lenses and highly variable magnification zoom lenses. This zoom lens system comprises a convergent lens group fixed during zooming, movable lens groups for zooming and an image-forming lens group. The movable lens groups comprise three groups including a first movable divergent lens group, a second movable convergent lens group and a third movable convergent lens group as arranged in the forward order. In the movable lens groups, an interval between the second movable convergent lens group and the third movable convergent lens group is increased on the wide angle side, whereby the movement value of the first movable divergent lens group is decreased. As the result, an entrance pupil position on the wide angle side is hardly changed, so that the distortional aberration can be corrected.

Abstract: A zoom lens system having a wide angle of view, a large diameter and a large zooming ratio in which the distortion is well corrected. The zoom lens system includes a movable lens group and a fixed lens group for zooming. A relay lens is provided behind the zooming lens group. A compensating lens having a small refractive power is inserted between the movable lens group and the fixed lens group and is moved in association with the zooming operation. The compensating lens consists of an aspherical lens of small refractive power or a group of spherical lenses having a small refractive power as a whole. The compensating lens is located at a position between the movable lens group and the fixed lens group where the light flux advancing along the optical axis of the zoom lens system converges to the image side.

Abstract: In a zoom lens system dividable into a zooming lens component which varies the magnification without moving the image plane and a relay lens component, at least a part of the relay lens component is made to have no power so that the axial movement thereof may not vary the focal length of the zoom lens system and is moved along the optical axis in association with the zooming lens component to compensate the fluctuation of aberration caused by the movement of the zooming lens component.