Projector having an inverted head optical arrangement
Assignee3M Innovative Properties Company
InventorsPatricia H. DeLuca, Dennis F. Vanderwerf
Life of this patent
Estimating the term…
Abstract
An overhead projector including a Fresnel lens, a single element meniscus projection lens having a concave side and a convex side, and a folding mirror placed in an optical path between the Fresnel lens and the projection lens. The projection lens is oriented to have the concave side optically facing the Fresnel lens. The optical design of the overhead projector follows the following equation, FFres=(FLens(MLens+1)/MLens−SLD)/(MFres+1), where the Fresnel lens has a focal length FFres, and a magnification MFres, the projection lens has a focal length FLens and a magnification MLens, and SLD is the distance from the stop position and the projection lens.
Claims17
An overhead projector comprising:
- a) a transmissive stage comprising a Fresnel lens;
- b) a projection head placed above the stage, the projection head comprising a mirror and a single element meniscus projection lens, the Fresnel lens focal point defining a projection lens stop position;
- c) wherein a light path is defined from the Fresnel lens to the projection head and onto a projection surface, wherein the mirror is placed before the projection lens along the light path and the stop position is between the projection lens and the mirror.
A projection system comprising:
- a) a Fresnel lens having a focal length FFres, and a magnification MFres;
- b) a projection lens having a focal length FLens and a magnification MLens, the Fresnel lens focus point forming a projection lens stop position;
- c) a mirror, placed in an optical path between the projection lens and the Fresnel lens;
- d) wherein, FFres=(FLens(MLens+1)/MLens−SLD)/(MFres+1), where SLD is the distance from the projection lens stop position to the projection lens and the stop position of the is between the mirror and the projection lens.
An overhead projector comprising:
- a) a Fresnel lens,
- b) a single element meniscus projection lens having a concave side and a convex side;
- c) a folding mirror placed in an optical path between the Fresnel lens and the projection lens;
- and
- d) wherein the projection lens is oriented to have the concave side optically facing the Fresnel lens.
- e) wherein, FFres=(FLens(MLens+1)/MLens−SLD)/(MFres+1), where the Fresnel lens has a focal length FFres, and a magnification MFres, the projection lens has a focal length FLens and a magnification MLens, and SLD is the distance from a stop position and the projection lens.
Dependencies are inferred from the claim text.