Abstract: A close-up attachment lens, for enabling close-up photograph along with a main lens, is arranged to be attached to the object side of said main lens. The close-up attachment lens comprises, in that order from the object side, a positive first lens element, a negative second lens element, and a positive third lens element formed as a meniscus lens that is convex on the image side. Furthermore, the close-up attachment lens satisfies the following conditions:0.005<d2/fA<0.040 (1)0.010<(d2+d4)/fA<0.060 (2)wherein:di designates the distance between the ith surface and (i+1).sup.th surface;fA designates the focal length of the attachment lens.

Abstract: An image magnification apparatus, for use in a video display system that displays an image of an object, comprising a connecting module for connecting the image magnifying apparatus to a lens module of the video display system, and an objective lens system for forming an optical image of the object. The apparatus also includes a conversion optical system for magnifying the optical image formed by the objective lens system. The conversion optical system further includes a first biconvex lens unit having a positive refractive power, a second biconvex lens unit having a positive refractive power, and a third biconcave lens unit having a negative refractive power.

Abstract: A telescope includes a master telescope whose aberration has been independently corrected and which has an objective lens and an ocular lens. A rear conversion lens is provided on the image side of the objective lens of the master telescope and is made of a single lens having a concave surface that faces an object side. The rear conversion lens meets the requirements defined by the following relationships: f.sub.o '/f.sub.o >1 and 0.5<(dx.sub.2 /dh.sub.2)/(dx.sub.1 /dh.sub.1)<1.3, wherein "f.sub.o " represents the focal length of the objective lens of the master telescope; "f.sub.o '" represents the resultant focal length of the objective lens of the master telescope and the rear conversion lens; "dx.sub.1 /dh.sub.1 " represents an inclination of an incident surface of the rear conversion lens at an incident point thereof, upon which light is incident at a height h.sub.1 ; "dx.sub.2 /dh.sub.

Abstract: An objective lens for microscopes has an optical unit removably disposed at the front end of the objective lens. The optical unit includes at least two kinds of optical elements having different optical properties. Thus, the objective lens for microscopes can always maintain good imaging performance in the case where either a glass or plastic vessel is used.

Abstract: A wide-conversion lens for attachment to a master lens system consists of a bi-negative first lens in a object side and a bi-positive second lens in a master lens side, and in the second lens its radii of curvature of both surfaces are selected the same.

Abstract: An afocal field of view and focal length converter for an optical lens system includes a cube-shaped frame that is interposed on an optical axis of the lens system. Lenses are mounted in four faces of the frame to provide two reversible afocal pairs and two faces are left empty. The frame is rotatable about a first axis to position the afocal pairs in the optical axis for one of four conversion positions, and about a second axis, perpendicular to the first axis, to rotate the empty faces in the optical axis for a no conversion position.

Abstract: A miniature fixed-focal-length lens system includes a lens group which consists of a plurality of lenses and has a positive refracting power and a stop disposed on the object side of the lens group. The lens nearest to the object in the lens group is a meniscus lens which is concave to front and has a positive refracting power and the lens remotest from the object in the lens group is a lens which is convex to rear and has a positive refracting power.

Abstract: An afocal optical module simulator (aoms) for use in conjunction with one or two other optical modules to simulate an afocal variator optical system. The aoms is comprised of an optical module having a front and a rear end, and includes a movable negative lens. The front end of the aoms includes a mechanism for securing a front optical module which may include as its rear most element a positive lens system which will be located juxtaposed to, but spaced from, the movable negative lens within the aoms. Similarly, the rear end of the aoms includes a mechanism for securing a rear optical module, which includes as its front most element a positive lens system which will be located juxtaposed to, but spaced from, the movable negative lens within the aoms.

Abstract: A focal length changeable lens system for use with an on-chip micro-lens equipped solid-state imaging device, whose exit pupil is located at a long distance and whose focal length is changeable between a long focal length and a short focal length. The lens system includes a first positive power lens group, a second positive power lens group and a third positive power lens group arranged in order from the object end. The lens system further includes an aperture stop fixedly disposed between the first and second lens groups where the subject focal point of the third lens group is positioned. When the second lens group is out of the optical axis, the lens system provides a long focal length, and when the first lens group is out of the optical axis, the lens system provides a short focal length.

Abstract: An attachment lens system comprising, in the order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power; having a negative refractive power as a whole; and adapted in such a manner that magnification thereof is changed by moving at least one of the first lens unit and the second lens unit along the optical axis so as to vary the airspace reserved between these lens units. This attachment lens system composes a lens system having a high vari-focal ratio when combined with a master lens system.

Abstract: An attachment lens system for close-up photography in use with a master lens system in such a fashion that the attachment lens system is attached to the front of the master lens system, comprising a first lens as a positive component, a second lens whose face on the object side is convex, the second lens serving as a positive component, a third lens whose face on the master lens side is concave, the third lens serving as a negative component, and the first to third lenses being arranged in this order from the object to the master lens system, and the specific conditions on the working distance, a negative power of the lens system of the attachment lens system on the master lens system side, and the thicknesses of the specific lenses contained in the attachment lens system being satisfied.

Abstract: An accessory lens for a far-infrared thermal imager which is quickly insted or removed to double the range. The accessory uses two or three element with alternating dielectric constants and combinations of spherical and aspherical surfaces.