Adaptor for overhead projector

An adaptor for use with an overhead projector to project photographic slides onto a viewing surface, the overhead projector including a platen and a light source for directing illumination through the platen, said adaptor comprising:

• a base including opaque means for covering the platen and intercepting substantially all of the illumination at the platen from the light source, and means defining an aperture in said covering means for admitting illumination from the light source through the aperture;
• a fresnel lens for condensing illumination admitted by said aperture;
• a slide holder on said base surrounding said aperture for positioning a photographic slide in the illumination admitted by said aperture;
• and,
• a projection lens coupled to said slide holder for projecting magnified images of slides in said holder onto a viewing surface.

Apparatus for converting an overhead projector for use with photographic slides, the projector including a platen, a light source for directing illumination along a path extending through and above the platen, and means for condensing the illumination to converge at a first distance above the platen, said apparatus comprising:

• means for shortening the convergence of the illumination to a second distance above the platen substantially half the first distance;
• means for locating a photographic slide in the illumination path approximate the platen;
• and,
• a projection lens having a focal length equal to said second distance for projecting onto a viewing surface magnified images of the photographic slide in said locating means.

Apparatus for converting an overhead projector for use with photographic slides, the projector including a platen, a light source for directing illumination along a path through and above the platen, and a first fresnel lens having a condensing power for converging the illumination at a first distance from the platen, said apparatus comprising:

• a second fresnel lens having substantially the same condensing power as the first fresnel lens for shortening the illumination convergence to a second distance from the platen;
• means for locating a photographic slide in the illumination path approximate the platen;
• and,
• a projection lens having a focal length equal to said second distance for projecting onto a viewing surface magnified images of the photographic slide in said locating means.

An adaptor for use with an overhead projector to project photographic slides onto a viewing surface, the overhead projector including a platen and a light source for directing illumination along a path through and above the platen, and a first fresnel lens having a condensing power for focusing the illumination to converge at a first distance from the platen, said adaptor comprising:

• a base including opaque means for covering the platen and intercepting substantially all of the illumination at the platen from the light source, and means defining an aperture in said covering means for admitting illumination from the light source through the aperture;
• a second fresnel lens having substantially the same condensing power as the first fresnel lens for shortening convergence of the illumination to a second distance from the platen substantially half the first distance;
• a slide holder on said base surrounding said aperture for positioning a photographic slide in the illumination admitted by said aperture;
• and,
• a projection lens coupled to said slide holder for projecting magnified images of slides in said holder onto a viewing surface.

Apparatus for converting an overhead projector for use to project slides onto a viewing surface the overhead projector including a platen and a light source for directing illumination along a path through and above the platen, said apparatus comprising:

• a base including opaque means for covering the platen and intercepting substantially all of the illumination at the platen from the light source, said covering means defining a center and an aperture offset from the center for admitting illumination from the light source through the aperture;
• a fresnel disk in said aperture including a plurality of arcuate, concentric lenslets convex toward the center of the covering means;
• a slide holder on said base surrounding said aperture for positioning a photographic slide in the illumination admitted by said aperture;
• and,
• projection optics coupled to said slide holder and including means for projecting magnified images of slides in said holder onto a viewing surface.

Apparatus for use with an overhead projector including a platen and a light source for directing illumination along a path through and above the platen and having a fresnel condensing lens including a plurality of circular, concentric lenslets defining a common center, said adaptor comprising:

• a base including opaque means for covering the platen and intercepting substantially all of the illumination at the platen from the light source, said covering means defining a center for location over the common center of the lenslets and three apertures disposed in a line, one aperture at the center of the covering means and the other two apertures on opposite sides of the center one, for admitting illumination from the light source through the apertures;
• a fresnel disk extending across the one and each of the other two apertures including a plurality of arcuate, concentric lenslets, the lenslets extending across the one aperture being concave toward the center of the covering means and the lenslets extending across the other two apertures being convex toward the center of the covering means;
• a slide holder on said base surrounding said aperture for positioning a photographic slide in the illumination admitted by said aperture;
• and,
• a projection lens coupled to said slide holder for projecting magnified images of slides in said holder onto a viewing surface.