A family of condenser lenses for an overhead projector (OHP) are designed to balance overall brightness in the projected image versus uniformity of illumination. The lenses are plano-convex and aspheric, and their conic constant is a function of the radius of curvature. The radius of curvature is further selected from a range which depends upon the size of the stage of the OHP. Preferred values of other parameters of the lens and OHP optical system are selected to complement the lens design. The lens is constructed of a heat-resistant material, such as borosilicate, to withstand the high temperatures generated by the incandescent lamp within the OHP base. Condenser lenses which are members of the described family provide performance, in terms of total luminous flux and uniformity of that flux, which is superior to the performance of previous designs.
The present invention includes a projector illumination system having a light source positioned between a condenser lens and a light-collecting reflector. The light source includes a bulb that is urged under compression against a surface of the condenser lens. The condenser lens receives a flow of cooling air over a surface opposite that against which the light source is in contact to minimize deformation of the condenser lens caused by heat emanating from the light source.
The present invention includes a projector illumination system having a light source positioned between a condenser lens and a light-collecting reflector. The light source includes a bulb that is urged under compression against a surface of the condenser lens. The condenser lens receives a flow of cooling air over a surface opposite that against which the light source is in contact to minimize deformation of the condenser lens caused by heat emanating from the light source.
A condenser lens for a projection system optimizes the amount of overall brightness directed toward an aperture and the uniformity of illumination at the aperture. The lens, when placed in the projection system, has a marginal ray which starts at the center of the light source, passes through the edge of the condenser lens, and intersects the region to be illuminated at or near its edge. The lens further has a relative zonal ray height which is selected based on the distance from the light source to the aperture. The condensing lens system is particularly useful in the construction of overhead projectors.
