Abstract: An automatic visibility regulator for a camera viewfinder includes a focusing detector system that is adapted to detecting whether or not an object image to be photographed, having passed through the viewfinder, is focused on the retina of the user's eyeball and a focal position shifting device adapted to shifting a focal position of an ocular system and thereby to shift a position at which the object image is focused. The focal position shifting device is actuated to shift the ocular system when the focusing detector system detects that the object image is not focused on the retina of the user's eyeball. The focal position shifting device is not actuated, and, consequently, the focal position of the ocular system is not changed, when the focusing detector system detects that the object image is focused on the retina.

Abstract: Described herein is a variable magnification duplicator lens system which is provided with, on the subject side of a stop, a front lens group including a 1st lens element consisting of a meniscus lens of positive power and facing the convex side thereof toward the subject, a 2nd lens element consisting of a meniscus lens of negative power facing the convex side thereof toward the subject, a 3rd lens element with positive power, and a 4th lens element with negative power, and on the image-forming side of the stop, a rear lens group including 5th, 6th, 7th, and 8th lens elements arranged symmetrically with the 1st to 4th lens elements of the front lens group, respectively. Of these lens elements, the 3rd to 6th lens elements and at least one of the 1st and 8th lens elements are movable.

Abstract: A variable scale duplicator lens system, including: front and rear lens group each consisting of three lenses and located on the opposite sides of a stop, the front group on the side of the subject and the rear group on the image-forming side; the front group on the subject side including a 1st lens consisting of a meniscus lens of positive power facing the convex side thereof toward the subject, a 2nd lens consisting of a meniscus lens having negative power facing the convex side thereof toward the subject, and a 3rd lens of positive power; the rear lens group including 4th to 6th lenses arranged symmetrically with the 1st to 3rd lenses of the front lens group, respectively. Of these six lens members, at least one of the 1st and 6th lenses is movable.

Abstract: A zoom lens system for use as a copying lens, for example, comprises first to sixth elements arranged in this order from front to rear with a stop disposed between the third and fourth elements. The first element is a positive lens convex to the front and the second element is a negative lens concave to the front. The first and second elements together form a first stationary lens group having negative power. The third element is a positive lens and forms a first movable lens. The sixth, fifth and fourth elements are reverse duplicates of the first, second and third elements. The fourth element forms a second movable lens, and the fifth and sixth elements together form a second stationary lens group. The lens system is axially movable as a unit between fixed image and object planes. The first and second movable lenses are axially movable in response to the axial movement of the entire lens system to vary the magnification of the image. The following three conditions are satisfied.0.4<fV/f.sub.1.0 <0.

Abstract: A zoom lens system in accordance with this invention is composed of a first fixed lens group, a first movable lens group, a second movable lens group and a second fixed lens group arranged in this order from front to rear, wherein a stop is are located at the center of the whole lens system and the first fixed lens group and the second fixed lens group consist of the same lens elements and located symmetrically with respect to the stop, and similarly the first movable lens group and the second movable lens group consist of the same lens elements and are located symmetrically with respect to the stop. The first movable lens and the second movable lens are asymmetrically moved with respect to the stop in accordance with the location of the whole lens system that is changed to vary the magnification, whereby the distortion and the focus shift caused by the field curvature fluctuation are eliminated throughout the variable range of magnification.

Abstract: A projection lens system comprises a positive meniscus lens G1 (as numbered consecutively from front to rear) convex to the front, a biconcave lens G2, a biconvex lens G3, a positive meniscus lens G4 convex to the front, and a biconcave lens G5. The projection lens system is designed to be well matched with the halogen lamp of cold mirror type in which the distance to the secondary focus is short by using a negative lens at the rear end thereof, making the Petzval sum small, locating the entrance pupil as near to the aperture as possible and shortening the back focal distance. The image surface is made flat and spherical aberration and astigmatism are well corrected. The high order comatic flares are markedly reduced and an image of high sharpness and contrast can be obtained thereby. Further, the radii of curvature of all the surfaces in the lens system are made not smaller than 0.68f so that the lenses can be manufactured at a low cost.