Abstract: A great aperture ratio zoom lens has, in succession from the object side, a first lens group of positive refractive power having a focusing function, a second lens group of negative refractive power having a magnification changing function, a third lens group of positive refractive power having a correcting function for keeping the image plane at a predetermined position, and a fourth lens group of positive refractive power having an imaging function. The first to third lens groups from a substantially a focal magnification changing portion. The fourth lens group includes, in succession from the object side, a forward group comprising a positive meniscus lens component having its convex surface facing the object side, a positive lens components having its surface of sharper curvature facing the image side, and a biconcave lens component, and a rearward group having a negative lens component and a positive lens component. The zoom lens satisfies certain conditions.

Abstract: A four-group zoom lens includes, in succession from the object side, a first group having a positive refractive power and movable on the optical axis for focusing, a second group having a negative refractive power and movable on the optical axis to vary the total focal length of the entire system, a third group having a positive refractive power and movable on the optical axis to keep the image plane at a predetermined position, and a fourth group as a relay lens system having a positive refractive power. The second group has a cemented lens component comprising three negative, positive and negative lenses cemented together and having a composite negative refractive power, and a negative lens component.

Abstract: A zoom lens has, in succession from the object side, a first lens group as a convergent focusing group, a second lens group as a divergent magnification changing group, a third lens group as a convergent correcting group, and a fourth lens group as a convergent relay system. The second group and the third group are movable relative to each other along the optical axis to thereby change the magnification while keeping the image plane at a predetermined position. During focusing to objects from infinity to a predetermined short distance, the first group is moved toward the object side and during focusing to an object at a distance still shorter than said predetermined short distance, the first group and the second group are moved along the optical axis at the same time while the third group is maintained at a predetermined position from the image plane.

Abstract: This specification discloses a large aperture ratio photographic lens with means for correcting aberrations comprising a forward group including at least one negative lens and having a composite positive refractive power, a rearward group also including at least one negative lens and having a composite positive refractive power, and a diaphragm provided between the two groups, characterized in that during the shift from an infinity object photography condition to a short distance object photography condition, focusing is effected by moving both of the two groups toward the object side while enlarging the diaphragm space between the two groups and that the photographic lens satisfies predetermined conditions.

Abstract: Compact lens systems capable of continuously effecting infinity photography to high magnification proximity photography and having a large aperture ratio and excellent imaging performance comprise, in order from the object side, a first convergent lens group, a second convergent lens group including a diaphragm, and a third divergent lens group. The first and second groups are movable toward the object side relative to the third group, while enlarging their spacing, when focusing is effected from infinity to a short distance.

Abstract: A lens system for photographing objects from infinity to a very short distance has a forward group having a positive refractive power, a rearward group disposed rearwardly of the forward group and having a positive refractive power, and a diaphragm member provided between the two groups. The forward group is movable by a predetermined distance along the optic axis of the lens system in accordance with the object distance for focusing. The rearward group is movable by an amount smaller than the amount of movement of the forward group in the direction of the optic axis in accordance with the object distance for focusing.

Abstract: A telephoto zoom lens comprises a variable power system and a relay lens system. The variable power system comprises a first group provided with a positive refracting power and capable of focusing by displacement along the optical axis, a second group provided with a negative refracting power and capable of continuously varying focal length by displacement along the optical axis and a third group provided with a positive refracting power and capable of maintaining the focal position constant regardless of the change in the focal length by displacement along the optical axis in cooperation with said second group, said system substantially constituting an afocal system to an infinite object.

Abstract: A rear conversion lens comprises a divergent forward lens group comprising three components and a divergent rearward lens group comprising two components. The three components forming the forward lens group are, in order from the object side, a biconvex positive lens, a biconcave negative lens with its more curved surface facing the image side, and a positive lens with its more curved surface facing the object side. The two components forming the rearward lens group are, in order from the object side, a biconcave negative lens with its more curved surface facing the image side and a biconvex positive lens with its more curved surface facing the object side.