Abstract: A projection optical apparatus has a projection optical system for projecting from a primary image an enlarged or reduced secondary image. A line connecting a center of an aperture diaphragm of the projection optical system to a center of an enlargement-side image plane forms a predetermined angle with respect to a normal to the enlargement-side image plane. The enlargement-side image plane and a reduction-side image plane are approximately parallel to each other. The projection optical system provides, on its enlargement side, curvature of field that is convex toward the projection optical system.

Abstract: A Zoom lens system, from the enlargement side, has the first to fourth lens units having the negative, positive, negative, positive optical power, respectively. The third lens unit has a meniscus lens having a convex surface on the enlargement side. The fourth lens unit has two positive lenses. During zooming from the shortest focal length condition to the longest focal length condition, the second and third lens units move along the optical axis so that a distance between the second and third lens units increases and a distance between the third and fourth lens units decreases. The zoom lens system fulfills the following conditions:0.30<.vertline..PHI.3.vertline..multidot.fs<0.903.ltoreq..vertline.(r.sub.MB +r.sub.MA)/(r.sub.MB -r.sub.MA).vertline.Here, .PHI.3 represents an optical power of the third lens unit; fs reprents a focal length of the entire zoom lens system in the shortest focal length condition; r.sub.MB and r.sub.

Abstract: An imaging optical system transmits a primary image. The optical system does not form an intermediate image. The primary image is projected on a screen as a secondary image. The optical system has a projection optical system and a reflection optical system. An optical axis of the reflection optical system forms an angle other than 90.degree. with respect to a screen-side image surface.

Abstract: An optical system projects an enlargement of an image of an object surface on a screen inclined relative to the object surface. The optical system includes an afocal first lens unit including a diaphragm and at least a second lens unit. The optical axis of the afocal system is not collinear with a normal line from the object surface, i.e., the afocal system is eccentric to the object surface. The second lens unit is eccentric relative to the afocal lens unit.

Abstract: A projecting optical device which simultaneously projects one object onto two or more different screens has a first screen, a second screen, a first projecting optical system which projects the object onto the first screen, and a second projecting optical system which projects the object onto the second screen and does not share an optical element with the first projecting optical system. A first base line connecting the center of the object to the center of the image projected on the first screen by the first optical system and a second base line connecting the center of the object to the center of the image projected on the second screen by the second optical system are not parallel to each other.

Abstract: A zoom lens system according to the present invention comprises, from the object side to the image side, a first lens unit with a positive refractive power including a negative high dispersion lens element and a positive lens element; a second lens unit with a negative refractive power consisting of two or three lens elements including a positive high dispersion lens element and a negative lens element, and having at least one aspherical surface; and a third lens unit with a positive refractive power consisting of five or less lens elements including a negative high dispersion lens element and one or two positive lens elements located on the object side of the negative high dispersion lens element, and having at least one aspherical surface. With the lens arrangement, a compact high-zoom-ratio zoom lens system having a high aberration correction performance is realized.

Abstract: A wide-angle zoom lens system comprises, from the object side to the image side, a first positive lens unit being stationary on an optical axis during a zooming operation, a second negative lens unit shifting along the optical axis during the zooming operation, a third positive lens unit being stationary on the optical axis during the zooming operation, and a fourth positive lens unit shifting along the optical axis during the zooming operation, wherein the refractive power of the first and second lens units fulfills the predetermined conditions.

Abstract: A variable lens system has three lens unit whose refractive powers are positive, negative and positive from an object side to the image side. Each lens unit consists of at least two lens elements. The central lens unit and the image side lens unit are shifted along an optical axis during a zooming operation. The lens system fulfills the conditions: ##EQU1## wherein fS, Z, and Y' represent the shortest focal length, a zoom ratio and an image height, respectively, of the lens system. .phi.1 and .phi.2 represent refractive powers of the object side and central lens units.