Abstract: A zoom lens of the negative lead type includes comprises, in order from an object side, a first lens unit of negative refractive power and a second lens unit of positive refractive power, variation of magnification being effected by varying a separation between the first lens unit and the second lens unit, the zoom lens satisfying the following conditions:3.ltoreq.NL1.ltoreq.4NL2.ltoreq.NL1where NL1 and NL2 numbers of lens elements which constitute the first lens unit and the second lens unit, respectively.

Abstract: In a camera of the kind arranged to obtain an object image through a photo-taking lens at an arbitrary image plane size on a photosensitive surface by using an image plane size varying member, either the nearest shootable distance of the photo-taking lens is arranged to become shorter than the normally nearest shootable distance or the magnification varying range of the power varying part of the photo-taking lens is arranged to be expanded on the wide-angle side, as the diagonal length of the image plane size becomes shorter.

Abstract: A zoom lens has, in succession from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power. The second and third lens units are moved to thereby effect zooming. When variations in the magnifications of the second and third lens units from the wide angle end to the telephoto end are Z.sub.2 and Z.sub.3, respectively, the zoom lens satisfies the condition that Z.sub.3 /Z.sub.2 >1.4. The zoom lens is compact and yet covers a wide angle range of an angle of view of 60.degree.-80.degree..

Abstract: A zoom lens having a first lens unit remaining stationary and having positive refracting power, a second lens unit having negative refracting power, a third lens unit having positive refracting power, a fourth lens unit having negative refracting power and a fifth lens unit remaining stationary and having positive refracting power to perform zooming by moving at least the second lens unit and the fourth lens unit and to perform focusing an infinite object to a nearest object by moving the fourth lens unit toward the image surface.

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: A zoom lens having a first lens unit remaining stationary and having positive refracting power, a second lens unit having negative refracting power, a third lens unit having positive refracting power, a fourth lens unit having negative refracting power and a fifth lens unit remaining stationary and having positive refracting power to perform zooming by moving at least the second lens unit and the fourth lens unit and to perform focusing an infinite object to a nearest object by moving the fourth lens unit toward the image surface.

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 rear-focus zoom lens system with four lens group. A stationary first lens group of a positive refractive power; a second lens group of a negative refractive power that moves for zooming; a stationary third lens group of a positive refractive power; a fourth lens group of a positive refractive power that moves for zooming and focusing. The first through fourth lens groups are arranged in that order from the object side. This zoom lens system also satisfies the following conditional expression:3.7<f.sub.4 /fw<6wherein f.sub.4 is the focal length of the fourth lens group and fw is the focal length of the zoom lens system at the wide-angle end.

Abstract: In a camera of the kind arranged to obtain an object image through a photo-taking lens at an arbitrary image plane size on a photosensitive surface by using an image plane size varying member, either the nearest shootable distance of the photo-taking lens is arranged to become shorter than the normally nearest shootable distance or the magnification varying range of the power varying part of the photo-taking lens is arranged to be expanded on the wide-angle side, as the diagonal length of the image plane size becomes shorter.

Abstract: A zoom lens comprising, from front to rear, a first lens group of negative power, a second lens group of positive power and a third lens group of negative power, wherein as zooming from the wide-angle end to the telephoto end is performed by moving the first, second and third lens groups, the second and third lens groups both are directed forward and the speed of movement of the third lens group is faster than that of movement of the second lens group, the zoom lens satisfying the following conditions:1<S1w/S2w<3.20.15<.vertline.f3.vertline./FT<0.432<FT/FW<5where S1w and S2w are air separations between the first and second lens groups and between the second and third lens groups in the wide-angle end respectively, f3 is a focal length of the third lens group, and FW and FT are shortest and longest focal lengths of the entire lens system respectively.

Abstract: A zoom lens comprising, from front to rear, a first lens unit of negative power, a second lens unit of positive power and a third lens unit of negative power, the second and third lens units being moved to effect zooming, and the third lens unit having its focal length f.sub.3 laid in the following range:0.5 f.sub.W <.vertline.f.sub.3 .vertline.<4 f.sub.Twhere f.sub.W and f.sub.T are the shortest and longest focal lengths of the entire system.

Abstract: A high-magnification zoom lens having a compact size has a front lens group of positive refractive power and a rear lens group of negative refractive power which groups are aligned in that order from the object side. The front lens group includes five lens elements and satisfies the following conditions.0.015<D2/fW<0.070.06<D3/fW<0.20.005<D5/fW<0.018where D2 is the air separation interval between the first and second lens elements; D5 is the air separation interval between the third and fourth lens elements; D3 is the center thickness of the second lens element; and fW is the focal length of the overall zoom lens system when it is set at its wide-angle end.

Abstract: A zoom lens comprising, from front to rear, a first lens unit of negative power, a seconde lens unit of positive power, a third lens unit of positive power and a fourth lens unit of negative power, wherein zooming from the wide-angle end to the telephoto end is performed by moving at least the second and fourth lens units toward the object side in such a way that the air separations between the first and second lens units and between the third and fourth lens units are shorter in the telephoto end than in the wide-angle end.

Abstract: A zoom lens of simple structure is disclosed comprising, from front to rear, a first lens unit of positive refractive power, a second lens unit of positive refractive power and a third lens unit of negative refractive refractive power, wherein these three lens units each are constructed from a single block, and zooming from the wide-angle end to the telephoto end is performed by moving the first and third lens units axially toward the object side independent of each other.

Abstract: This specification discloses a magnification changing lens which has, in succession from the object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive or negative refractive power and in which at least the second and third lens unit are moved toward the object side to thereby accomplish the magnification change from the wide angle end to the telephoto end. This magnification changing lens particularly satisfies the following condition:0.13<bf.multidot.min/fw<0.7,where bf.multidot.min is the shortest distance of the back focus in the whole magnification change range and fw is the focal length of the entire system at the wide angle end.

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.

Abstract: A zoom lens including at least two lens units of which the front one is of positive refractive power and the rear one is of negative refractive power, the units being axially movable to decrease their separation in zooming from the wide angle to the telephoto end. At least one of the lens units is provided with at least one refractive index distribution type lens arranged on a common optical axis of the other lenses in order to achieve a great advance in compactness.

Abstract: An optical system housed within a waterproof package includes, from front to rear, front lens and a rear group of lenses. For both of the front and rear surfaces of the front lens, proper numerical limits of the refractive power of the rear lens group are given to provide an amphibious camera which give a proper optical performance not only in the air but also under water without the necessity of focus adjustment.