Abstract: A lens incorporates a plurality of lens units including at least one movable lens unit which is movable to change one of the functions of the lens. The lens has an optical low-pass filter on the side of the movable lens unit which is closer to an object. The optical low-pass filter separates a light incident upon it into at least two rays of light and emits the rays in at least in two different directions. The lens is characterized in that, when a coefficient l is given by:l=S+G-SG/Fwhere F is the focal length of the lens unit disposed on the side of the optical low-pass filter closer to an image forming surface, G is the distance between the front principal plane of the lens unit and the optical low-pass filter, S is the distance between the rear principal plane of the lens unit and the image forming surface, the lens unit satisfiesl.sub.MIN /l.sub.MAX >0.7where l.sub.MAX is the absolute maximum value of l obtained in the overall movable states available in the lens, and l.sub.

Abstract: An optical low-pass filter formed in a trapezoid wave profile having the top and bottom sides of lengths "a" and "b" respectively, a height ".delta." thereof and a length of one period thereof and made from a material having a refractive index "n", and satisfying the following conditions: for a wavelength of .lambda..sub.M .gtoreq.1.6 .lambda.m, ##EQU1## wherein .lambda..sub.M and .lambda.m are respectively maximum and minimum wavelengths in a wavelength range in which the filter works, and MIN(x,y) represents the smaller one of values which variables x and y take.

Abstract: For a single lens reflex camera in which an image bearing beam from the photographic objective is reflected by a movable mirror to the finder system, techniques are disclosed that the mirror is made half-reflective, and the transmitted light of the mirror is conducted by a supplementary optical member consisting of, at least, a prism fixedly secured (not movable relative) to the mirror toward an image sensor such as that of a focus detector positioned outside the optical axes of the objective and finder, that the movable mirror is made to take a quite different direction of movement from that to which the reflected beam from the mirror goes, and that as an image pickup device such as CCD is arranged on the optical axis of the objective and behind the movable mirror, the optical characteristics of optical members such as a filter positioned in front of the image pickup device are made equivalent to those of the supplementary optical member.

Abstract: A photographic lens of long back focal length comprising, from front to rear, a first lens unit of negative refractive power, the first lens unit including a first lens of positive refractive power whose front surface is convex toward the front, a meniscus-shaped second lens of negative refractive power convex toward the front and a third lens whose front surface is concave toward the front, a stop for determining F-numbers, and a second lens unit of positive refractive power having a plurality of lenses.

Abstract: An image pickup system includes a camera body having an image conversion device and a signal processor and a detachable lens including a memory and circuitry for transmitting the memory contents to the camera body signal processor. In one embodiment, the system provides for storage in the lens memory of the spectral characteristics of both the lens and the image conversion device. In a second embodiment, the system provides for storage of spectral characteristic data concerning a plurality of different lenses in memory in the camera body, with the lenses adapted for self-identification. In a third embodiment, camera body memory stores a single lens spectral characteristic for use in common with any one of plural lenses and representative of all such lenses.

Abstract: A wide angle zoom lens of increased back focal distance 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 positive power, the first and second lens units axially moving in differential relation to effect zooming, while holding the third lens unit stationary, and satisfying the following conditions:2.0.ltoreq..vertline.f.sub.1 /f.sub.W .vertline..ltoreq.3.20.33.ltoreq..vertline.f.sub.1 /f.sub.2 .vertline..ltoreq.0.8where f.sub.1 and f.sub.2 are the focal lengths of the first and second lens units, respectively, and f.sub.W is the shortest focal length of the entire lens system.

Abstract: This invention is based on the discovery of the fact that a proportional relationship exits between a reciprocal of an exit pupil of a photographic lens and an error in light measurement value and provides a camera which is characterized by the provision of means for measuring light of a beam passing through a photographic lens into the camera and deciding an exposure value, means for generating an information corresponding to the reciprocal of the exit pupil of the photographic lens and means for applying correction to said exposure value on the basis of the information generated by said information generating means.