In a system of overhead projection there is provided a horizontal stage on which is to be placed an object to be imaged. Means for illuminating the object is mounted below the stage at an angle thereto, while a projection lens system is installed above the stage and parallel thereto, in such a position that the axis of the light from the illumination means passes at an angle through its center. A mirror mounted above the lens system projects the undistorted image of the object onto a vertical screen. In another system of overhead projection based on the same principles, the stage and the projection lens system are inclined relative to the illumination means while themselves kept parallel to each other. The axis of the light from the illumination means in this instance extends vertically upwardly and passes at an angle through the center of the lens system. There are further disclosed herein some overhead projectors constructed in accordance with these systems of the invention.
A projecting optical apparatus has a light source which is located above a document supporting plate to illuminate a document located on the document supporting plate. A projecting lens system is located above the document supporting plate to project an image of the document on a projection screen. A reflection mirror reflects the light transmitted through the projecting lens system toward the projection screen to make an image on the projection screen. The projecting lens system and the reflection mirror are incorporated in a projecting reflection unit, so that the projecting reflection unit is movable in directions substantially parallel with the plane of the document supporting plate.
Projection apparatus comprises a projection lens arranged to project an image from the apparatus and an image carrier (such as an L.C.D. array, film or slide) which is retained in the apparatus in such a way so as to be tiltable about a pivot axis. Because the image carrier is tillable, "keystone effect" typical of projected images may be reduced or substantially prevented. The projection lens is preferably tiltable also and coupled to the tilting of the image carrier to reduce further "keystone effect" and improve image resolution.
A multimedia projector comprises a optical frame that mounts, from back to front, a light source, a back fresnel lens, a back polarizer, an LCD display object, a front polarizer, a front fresnel lens, and a front lens group for projecting images formed by the LCD display object. To provide keystone distortion correction of projected images, the front fresnel lens is manually and selectively tiltable about an axis extending parallel with the plane of the LCD display object. The selective tilting is accomplished by a manually movable fresnel actuator with a cammed surface. A control arm extends between the fresnel actuator and the fresnel lens, and rides on the cammed surface such that a relatively large movement of the fresnel actuator produces a relatively small adjustment in tilt of the fresnel lens in order to permit fine adjustment of the fresnel lens tilt. To provide contrast adjustment, a contrast adjustment mechanism is attached to the back polarizer to permit the manual selective tilting of the back polarizer about an axis extending perpendicular to the front polarizer, in order to optimize contrast of images projected by the front lens group.
An overhead projector has a flat stage, for placing a sheet material thereon, which is inclined such that a normal line of the flat stage, which is in alignment with the optical axis of the projection lens, inclines an angle relative to a vertical line so that a reflection mirror disposed above the projection lens at an angle of 45 degrees directs an image projected by the projection lens toward a remote screen at a desired angle of elevation.
A projector for projecting a successive series of pictures and, in particular, an audiovisual information device, includes a housing, a projector disposed within the housing and a projection face which is provided in close proximity to the rear side of the housing for azimuthal projection. The projector face can be viewed by at least one window opening provided on the front side of the housing and the projector is arranged outside of the viewing range between the window opening and the projection face. The projector has a projection axis which is disposed at an angle with respect to the optic axis of its lens. The projector is especially suitable for both indoor and outdoor use.
