Abstract: The invention relates to an image pickup optical system which can make a sensitive tradeoff between the precision of alignment of a decentration optical prism used as an image formation element for an electronic camera or the like with respect to an image pickup element and ease of fabrication. The invention provides an optical prism 100 comprising three optical surfaces 12 to 14. An entrance surface 14 is suitable for incidence of light from a subject. The incident light is subjected to at least two internal reflections to turn back an optical path. The reflected light leaves the prism through an exit surface 12 to form an image of the subject on an image pickup surface 21 located outside of the prism. At least one of the entrance surface 14 and exit surface 12 is constructed of an optical surface having a combined transmission and internal reflection action. The optical prism is used in combination with a prism frame 30 designed to be well fit therefor.

Abstract: A high-performance and low-cost image-forming optical system having a minimal number of constituent optical elements and made compact and thin by folding an optical path using reflecting surfaces arranged to minimize the number of reflections. The image-forming optical system has a first prism, a stop, and a second prism. The first prism has a first transmitting surface, a first reflecting surface, a second reflecting surface of positive power, and a second transmitting surface. The second prism has a first transmitting surface, a first reflecting surface, a second reflecting surface of positive power, and a second transmitting surface. The first transmitting surface and second reflecting surface of the first prism are the identical surface, and the first reflecting surface and second transmitting surface of the second prism are the identical surface. The image-forming optical system is approximately telecentric on the image side.

Abstract: An object of the invention is to provide a compact yet high-performance finder optical system comprising an image inversion optical subsystem having a decentered reflecting surface, which enables a bright, distortion-free image to be observed. This object is achieved by locating a rotationally asymmetric surface in the image inversion optical subsystem forming part of the finder optical system.

Abstract: A high-performance and low-cost image-forming optical system made compact and thin by folding an optical path using reflecting surfaces having power. The optical system has a plurality of reflecting surfaces having power. Among the reflecting surfaces, a reflecting surface (12) of negative power is placed closest to the object side, and a reflecting surface (22) of positive power is placed closer to the image side than the reflecting surface (12). At least one reflecting surface (13) is provided between the reflecting surface (12) and the reflecting surface (22). An axial principal ray (1) incident on the reflecting surface (13) satisfies the condition of 45.degree.<.vertline..theta..vertline., where .theta. is the angle formed between the axial principal ray and a line normal to the reflecting surface (13) in the decentration direction at a point where the axial principal ray (1) intersects the reflecting surface (13).

Abstract: A compact, thin and low-cost image-forming optical system having an optical low-pass filter, and an apparatus using the image-forming optical system. The image-forming optical system for forming an image of an object includes a stop (2), a first prism (10) placed closer to the object side than the stop (2), and a second prism (20) placed closer to the image side than the stop (2). The first prism (10) has object-side reflecting surfaces (12, 13) with an aspherical surface configuration that reflect a light beam in the prism and give a power to the light beam when reflecting it. The second prism (20) has image-side reflecting surfaces (22, 23) with an aspherical surface configuration that reflect a light beam in the prism and give a power to the light beam when reflecting it. A low-pass filter (4) for cutting off a high-frequency component is provided between the object-side reflecting surfaces (12, 13) and the image-side reflecting surfaces (22, 23).

Abstract: A real-image finder optical system having an objective optical system, an image-inverting optical system, and an ocular optical system, wherein a power is given to a reflecting surface of the image-inverting optical system that is closer to the observer side than an intermediate image, thereby achieving an increase in the finder magnification. The objective optical system has a plurality of lens units. When zooming from the wide-angle end to the telephoto end is performed, the spacing between the plurality of lens units is changed. The image-inverting optical system has a plurality of reflecting surfaces. Of the reflecting surfaces, at least one reflecting surface closer to the ocular optical system than the object image is formed from a curved reflecting surface that gives a power to a light beam. The image-inverting optical system has a rotationally asymmetric surface that corrects rotationally asymmetric decentration aberrations produced by the curved reflecting surface.

Abstract: A high-performance real-image finder with a zoom objective optical system wherein a power is given to a reflecting surface of an image-inverting optical system to reduce the size in the direction of the thickness, and at the same time, a rotationally asymmetric surface is used in the image-inverting optical system to correct rotationally asymmetric decentration aberrations. The zoom objective optical system Ob has a first lens unit G1 of negative power, a second lens unit G2 of positive power, and a third lens unit G3 of positive or negative power. The real-image finder further includes an image-inverting optical system PP for erecting an intermediate image formed by the objective optical system Ob, and an ocular optical system Oc having a positive refracting power. At least one of reflecting surfaces S.sub.8 and S.sub.

Abstract: An optical low pass filter having an optical axis common to an imaging optical system or configured as a portion of an imaging optical system for contribution to formation of an image, functioning to image components in a longitudinal direction of the image pickup device onto a desired imaging location and having refractive powers, for components in different directions, which are different from that for the components in the longitudinal direction. This optical low pass filter is suited for use with line sensors.

Abstract: The invention provides a compact, lightweight yet low-cost zoom lens system which has a zoom ratio of at least about 2 and is well corrected for various aberrations, and in which sufficient attention is paid to temperature compensation when plastic lenses are used. The zoom lens system comprises in order from an object side a front lens group GF including a plurality of positive lenses containing at least a plastic lens and having a positive refracting power as a whole, and a rear lens group GR composed only of a plurality of negative lenses containing at least a plastic lens, wherein zooming is carried out by varying the spacing between the front and rear lens groups, and all the lenses satisfy the following condition (1):n.sub.d <1.75 (1)where n.sub.d is the d-line indices of refraction of the lenses.

Abstract: An optical system comprising a plural number of lens elements at least one of which is designed as a graded refractive index lens element having refractive index distribution in the radial direction, and has aberrations favorably corrected in said optical system as a whole by making most of the correcting functions of the graded refractive index lens element for Petzval's sum and chromatic aberration.

Abstract: The invention provides a zooming lens system which covers a wide-angle zone, has a zooming ratio of approximately 3 or higher, and is well corrected for various aberrations. This system comprises, in order from the object side, a first lens unit I having positive refracting power, a second lens unit II having negative refracting power, a third lens unit III having positive refracting power, a fourth lens unit IV having positive refracting power and a fifth lens unit V having positive refracting power, with at least said first, third, fourth and fifth lens units being moved toward the object side for zooming from the wide-angle end to the telephoto end, and conforms to the following conditions:-0.8<f.sub.2 /f.sub.W <-0.5 (1)-0.7<f.sub.T12 /f.sub.T <-0.3 (2)Here f.sub.2 is the focal length of the second lens unit, f.sub.W is the focal length of the entire system at the wide-angle end, f.sub.T12 is the composite focal length of the first and second lens units at the telephoto end, and f.sub.

Abstract: A wide-angle lens system comprising, in order from the object side, a front unit, a stop and a rear unit: the front unit comprising, in order from the object side, a first lens unit which comprises a plurality of lens components including a positive lens component and has a negative refractive power as a whole, a negative lens component having a concave surface on the object side and a cemented lens component; and the rear unit comprising a negative lens component disposed on the side of the stop and at least two positive lens components. This wide-angle lens system has sufficiently corrected aberrations, in particular, negative distortion, curvature of field and sagittal coma.

Abstract: An optical system comprising a plural number of lens elements at least one of which is designed as a graded refractive index lens element having refractive index distribution in the radial direction, and has aberrations favorably corrected in said optical system as a whole by making most of the correcting functions of the graded refractive index lens element for Petzval's sum and chromatic aberration.

Abstract: An optical system comprising, in the order from the object side, an objective lens unit having a positive refractive power, a relay lens unit having a positive refractive power and an eyepiece lens unit having a positive refractive power, adapted in such a manner that an inverted image formed by the objective lens unit is inverted once again by the relay lens unit for forming an erect image, using at least one graded refractive index lens element in the relay lens unit, and having a small number of lens elements or a high magnification and favorably corrected aberrations.

Abstract: A compact vari-focal lens system comprising, in the order from the object side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power and a third lens unit having a negative refractive power, and uses at least one radial type graded refractive index lens element arranged at the image side location in the second lens unit. The vari-focal lens system has a high vari-focal ratio and aberrations corrected favorably over the entire vari-focal range from the wide position to the tele position, and consists of a very small number of lens elements.

Abstract: An optical system comprising a plural number of lens elements at least one of which is designed as a graded refractive index lens element having refractive index distribution in the radial direction, and has aberrations favorably corrected in said optical system as a whole by making most of the correcting functions of the graded refractive index lens element for Petzval's sum and chromatic aberration.

Abstract: The invention provides a compact, light-weight varifocal lens system that has a varifocal ratio of about 3, comprises fewer lenses than in the prior art, has a short total length and is well corrected in terms of various aberrations from the wide angle to telephoto ends. This lens system comprises a first positive lens unit G1, a second positive lens unit G2 and a third negative lens unit G3, wherein varifocal motion is achieved by moving each unit in such a way that, from the wide angle to telephoto ends, the air space between the first and second lens units increases, while the air space between the second and third lens units decreases.

Abstract: A compact vari-focal lens system comprising, in the order from the object side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power and a third lens unit having a negative refractive power, and uses at least one radial type graded refractive index lens element arranged at the image side location in the second lens unit. The varifocal lens system has a high vari-focal ratio and aberrations corrected favorably over the entire vari-focal range from the wide position to the tele position, and consists of a very small number of lens elements.

Abstract: A vari-focal lens system including, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, an aperture stop, a third lens unit having a positive refractive power and a fourth lens unit having a negative refractive power; and using at least one radial GRIN lens element on each side of the aperture stop. This vari-focal lens system has only a very small number of lens elements and had favorably corrected aberrations.

Abstract: An imaging lens system comprising, in the order from the object side, a first lens component having a convex surface on the object side and a positive refractive power, a second lens component having a concave surface on the image side and a negative refractive power, and a third lens component. Through the imaging lens system is of a triplet or Tessar type, the lens system is designed so as to have a high aperture ratio and favorably corrected coma by arranging a radial GRIN lens element having a concave surface on the image side and a positive refractive power at the most image side location in the third lens component.