A projection optical device includes a projection optical system for projecting an image of an object plane onto a screen without forming an intermediate real image. The projection optical system includes a coaxial first lens group to be arranged relatively near the object plane, a coaxial second lens group to be arranged relatively near the screen, and a stop arranged between the first and second lens groups. The second lens group has an optical axis inclined with respect to an optical axis of the first lens group. A magnification .beta.1 of the first lens group satisfies a relationship of .vertline.1/.beta.1.vertline.<0.05. The second lens group is angularly deviated from the first lens group around a position of the stop.

A pupil conjugate-coupling device in a projecting optical system includes a first projection lens system which forms an intermediate image of an image indicating element, a second projection lens system which projects the intermediate image onto a screen, said first and second projection lens systems having optical axes intersecting at a predetermined angle, and an optical element having structural periodicity positioned between the first and second projection lens systems. The optical element has a positive power and a prism function for deflecting a bundle of rays transmitted through the first projection lens system towards the optical axis of the second projection lens system to thereby couple pupils of the first and second projection lens systems. The optical element is deviated from an intermediate image forming position by a predetermined offset in the optical axis direction thereof.

A projector (100) including an liquid crystal display image source (120), a field lens (126), and a projection lens (128) projects a full-color image by projecting and converging images of multiple liquid crystal displays ("LCDs"). The image is properly positioned without keystoning by tilting the field lens and offsetting the center of the LCD image source from the optical axis (142) of the projection lens. Trapezoidal error is eliminated by maintaining the optical center (156) of the field lens on the optical axis of the projection lens. During focusing, a mounting apparatus (164) adjusts the offset (154) between the center of the LCD and the optical axis of the projection lens for proper convergence of the images and maintains the optical center of the field lens on the optical axis of the projection lens.

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.

The present invention includes an invertible and orthoscopic LCD projector having a LCD panel for providing display information that is projected toward a display screen to form a display image. In a preferred embodiment, a converging Fresnel lens is positioned to receive the display information from the LCD panel and form a display object corresponding to the display image. The converging Fresnel lens has an optical center offset from the optical center of the LCD panel in an elevation direction and defines a projection optical axis that extends toward the display screen along an elevation angle in the elevation direction. The Fresnel lens is tilted automatically about a tilt axis transverse to the projection optical axis and the elevation direction by an amount proportional to the elevation angle to cooperate with the offset of the Fresnel lens optical center to form an orthoscopic display image.