Abstract: A zoom lens of the rear focus type is disclosed, whose back focal distance is increased to accommodate a three-color separation prism and other optical elements, comprising, 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, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, the second lens unit and the fourth lens unit being moved to effect zooming and the fourth lens unit being moved to effect focusing, wherein the third lens unit has a negative lens disposed closest to the object side and having a concave surface facing the object side and has a positive lens disposed closest to the image side, and a lens surface on the image side of the positive lens has a refractive power which is stronger than that of a lens surface on the object side of the positive lens.

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, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, zooming from a wide-angle end to a telephoto end being effected by moving the second lens unit toward the image side, and shifting of an image plane due to zooming being compensated for by moving the fourth lens unit, wherein the second lens unit consists of four separate single lenses including three negative lenses and one positive lens, and the third lens unit has at least one positive lens both surfaces of which are aspherical.

Abstract: A zoom lens of the rear focus type having an increased range with the back focal length long enough to accommodate a color separation prism, 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, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, the second and the fourth lens units moving axially to effect zooming and the fourth lens unit moving axially to effect focusing, wherein the second lens unit is constructed with a negative first lens, a negative second lens, a negative third lens and a positive fourth lens.

Abstract: A zoom lens of the retrofocus type includes, in order from a longer-distance conjugate point side to a shorter-distance conjugate point side, a front lens unit of negative refractive power, and a rear lens unit of positive refractive power, wherein a separation between the front lens unit and the rear lens unit varies according to variation of magnification, and at least one of the front lens unit and the rear lens unit is provided with a diffractive optical element.

Abstract: In a camera having a first image pickup device arranged to pick up a still image by using a silver-halide film, a second image pickup device arranged to electrically pick up a moving image by using a photoelectric conversion element, and an image pickup optical system arranged to guide an image light flux both to the first image pickup device and the second image pickup device, the image pickup optical system includes a fixed half mirror for guiding the image light flux both to the first image pickup device and the second image pickup device, a first light quantity adjusting device provided for the first image pickup device, and a second light quantity adjusting device provided for the second image pickup device.

Abstract: A camera includes a fixed first mirror for both reflecting a light flux and transmitting the light flux therethrough, a second mirror for reflecting a part of the light flux transmitted through the first mirror toward a particular device, the second mirror being capable of moving between a non-exposure position and a mirror-retracted position, and a light blocking member movable in interlocked relationship to a movement of the second mirror in such a manner that, when the second mirror is located at the non-exposure position, the light blocking member is located at a light blocking position at which the light blocking member blocks at least a part of the light flux transmitted through the first mirror, and, when the second mirror is retracted to the mirror-retracted position, the light blocking member moves to a retracted position at which the light blocking member is retracted from the light blocking position.

Abstract: A zoom lens includes, from front to rear, 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, at least the second and fourth lens units being moved to effect zooming, wherein the maximum image angle is increased while the diameter of the first lens unit is extremely reduced.

Abstract: A zoom lens of the rear focus type including, from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power having a stop, and a fourth lens unit of positive refractive power. During zooming from a wide-angle end to a telephoto end, the second lens unit is moved toward the image side, the third lens unit and the stop are moved in unison in a locus convex toward the object side, and the fourth lens unit is moved in a locus convex toward the object side. During focusing, the fourth lens unit is moved, and the following condition is satisfied: -0.3<M3max/.phi..sub.1 <-0.04, where M3max is a maximum value of an amount of axial movement of the third lens unit and the stop from the wide-angle end (a moving direction to the object side being taken as "-"), and .phi..sub.1 is the outer diameter of a frontmost lens of the zoom lens.

Abstract: A zoom lens includes, from front to rear, 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, at least the second and fourth lens units being moved to effect zooming, wherein the maximum image angle is increased while the diameter of the first lens unit is extremely reduced.

Abstract: A zoom lens includes, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, zooming being performed by moving the second and fourth lens units, and focusing being performed by moving the fourth lens unit, wherein the second lens unit is constructed from three single lenses, i.e., from front to rear, a negative first lens having a strong concave surface facing the image side, a negative second lens of bi-concave form and a positive third lens having a strong convex surface facing the object side.

Abstract: A zoom lens of the rear focus type is disclosed comprising, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, the second and fourth lens units axially moving to effect zooming, and the fourth lens unit axially moving to effect focusing. The third lens unit includes at least one positive lens at a front position and a negative lens of meniscus form concave toward the image side at a rearmost position. The fourth lens unit includes one negative lens and two positive lenses. The focal lengths f3 and f4 of the third and fourth lens units, respectively, satisfy the following condition:0.73<f3/f4<1.00.

Abstract: A zoom lens includes, in the order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power. The first and third lens units are stationary. The second lens unit is moved in one direction to vary the magnification. The fourth lens unit is moved so as to compensate for the shift of an image plane resulting from the variation of the magnification, and focusing is performed by moving the fourth lens unit. The third lens unit has a bi-convex lens and a negative meniscus lens having a strong concave surface facing the object side, and the fourth lens unit has a negative meniscus lens having a strong concave surface facing the image side, a bi-convex lens and a positive lens having a strong convex surface facing the object side.

Abstract: A zoom lens having four groups and wherein at least one of the four groups is equipped with an index distribution type lens. A first lens group has a positive refracting power; a second group has a negative refracting power; a third lens group has a positive refracting power; and a fourth lens group has a positive refracting power. The first through fourth lens groups are arranged in this order from the object side, and the second group is moved to perform zooming while the fourth lens group is moved to compensate for image plane fluctuation which is incident to the zooming and also to perform focusing.

Abstract: This specification discloses an image stabilizing photo-taking lens system having a lens system in which a plurality of lens units are disposed and at least one lens spacing is changed to change the focal length, and a variable vertical angle prism unit whose vertical angle is changed and driven to refract the optic axis immediately rearwardly of a predetermined lens surface which satisfies the condition that .vertline.Fa.vertline.<10 Ft, where Fa is the combined focal length from the front lens surface of the lens system to the predetermined lens surface, and Ft is the focal length of the entire lens system at the telephoto end thereof.

Abstract: A zoom lens is disclosed comprising, from front to rear, a first lens unit of positive power, a second lens unit of negative power, a third lens unit of negative power and a fourth lens unit of positive power, zooming being performed by moving the second and third lens units axially in differential relation, whereby the focal length F2 of the second lens unit lies in the following range:0.09<.vertline.F2/FT.vertline.<0.14where FT is the longest focal length of the entire lens system. With this, though the optical total length is shorter than ever, the zoom lens gets a higher range of variation of the focal length.

Abstract: A zoom lens of the rear focus type of the invention comprises, from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power. The second lens unit is moved toward an image side to effect zooming from a wide-angle end to a telephoto end, while an image shift resulting from the zooming is compensated for by moving the fourth lens unit, and focusing is performed by moving the fourth lens unit. Letting the focal length of the i-th lens unit be denoted by F.sub.i, the local length of the entire lens system in the telephoto end by F.sub.T, the F-number at full open aperture in the telephoto end by F.sub.

Abstract: In an optical system arranged to detect a distance to an object to be photographed by projecting beams of light from a light emitting element which emits visible light or infrared rays or the like and by receiving reflected light from the object at a light receiving element, a light projecting lens system having a plurality of optical axes is arranged in front of the light emitting element to have a spherical or aspherical surface on the side of the object and a plurality of planes for forming the plurality of optical axes on the side of the light emitting element.

Abstract: A zoom lens comprising, from front to rear, a first lens group of positive power, a second lens group of negative power axially movable for zooming, a third lens group axially movable for compensating for the image shift resulting from the movement of the second lens group, a fourth lens group of positive power, optical filter means and a fifth lens group of positive power, and satisfying the following condition:0.7<f4/L<0.95where f4 is the focal length of the fourth lens group and L is the distance from an image point formed by the first to third lens groups to the front principal point of the fourth lens group.

Abstract: A zoom lens comprising a first lens unit of positive power, a second lens unit of negative power as the variator, a third lens unit of negative power as the compensator, and a fourth lens unit of positive power stationary during zooming, the fourth lens unit being composed of a bi-convex first lens, a positive second lens, a negative third lens of strong concave curvature at the front, a positive fourth lens, a fifth lens of strong concave curvature at the rear, and a positive sixth lens, and satisfying the following condition:0.5<D/Fw<1.5where D is the air separation between the fourth and fifth lenses, and Fw is the shortest focal length of the entire lens system.

Abstract: A zoom lens comprising a plurality of lens units in which at least one of the air separations between the units is varied to effect zooming, whereby at least one of the plurality of lens units is included with at least one refractive index distribution type lens element on a common optical axis of the other elements.