Transparency overhead projector

• US 4,952,053 A
• Filed: 08/22/1988
• Issued: 08/28/1990
• Est. Priority Date: 08/24/1987
• Status: Expired due to Fees

• Current Assignee: Procent Patent-Und Verwaltungs AG Dufor STR
• Original Assignee: Procent Patent- und Verwaltungs AG
• Inventors: Behr, Karl-Gunther
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/234,592
• Time in Patent Office: 736 Days
• Field of Search: 353/65, 353/77, 353/78, 353/99, 353/122, 353/DIG. 3, 350/612, 350/613, 350/616, 350/625, 350/627
• US Class Current: 353/65
• CPC Class Codes: G03B 21/132 Overhead projectors, i.e. capable of projecting hand-writing or drawing during action epidiascopic projectors G03B21/08
• CPC Class Codes: Y10S 353/03 Transparent

Abstract

The invention concerns a transparency overhead projector having an illumination unit of which the height has been extremely reduced. The main component of the illumination unit is a specular surface comprising mutually parallel, mirrorized prismatic shoulders either on its top or on its lower side, which reflect the light from at least one lateral source toward the Fresnel lens, the platen and the projecting lens. The specular surface may be plane, however it may also be curved in circular, hyperbolic etc. manner in the longitudinal direction of the prismatic shoulders. This curvature may be constant or it may vary. Further, the specular surface also may be twisted, that is, it may also be curved in a direction orthogonal to the prismatic shoulders, and this curvature also may be constant or variable. However the prism angles of the individual prismatic shoulders are always individually determined so that the light shall appear to come from a source which seems to be mounted centrally along the optical axis underneath the Fresnel lens.

Claims

1. An overhead projector having an optical axis, and comprising:

a base;

a light source;

a transparent platen supported on said base along said optical axis;

an objective lens supported above said platen;

a fresnel lens also supported along said optical axis and beneath said platen; and

,

a specular surface mounted beneath said fresnel lens having mirrorized prismatic shoulders located on a top surface thereof which reflect light from said light source towards said platen and fresnel lens so that said reflected light appears to come from a light source positioned along said optical axis and beneath said fresnel lens, and wherein

said specular surface is curved in a first direction with respect to said platen and said curvature is variably concave and convex.

2. An overhead projector as recited in claim 1, wherein:

said specular surface is also curved in a second direction.

3. An overhead projector as recited in claim 2, wherein:

said second direction of curvature is orthogonal to said first direction.

4. An overhead projector as recited in claim 2, wherein:

said curvature in said second direction is not constant.

5. An overhead projector as recited in claim 2, wherein:

said curvature in said second direction is not constant and varies from concave through null to convex.

6. An overhead projector as recited in claim 3, wherein:

said curvature in said second direction is not constant and varies from concave through null to convex.