Optical: systems and elements – Projection screen – Unitary sheet comprising plural refracting areas
Reexamination Certificate
1999-01-13
2002-06-18
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural refracting areas
C359S457000, C359S742000
Reexamination Certificate
active
06407859
ABSTRACT:
BACKGROUND
The present invention is directed generally to a Fresnel lens for use with projection screens, and particularly to a Fresnel lens that reduces the effect of ghost images.
Fresnel lenses are often used in projection screens for collimating light received from the illumination source. The Fresnel lens is typically used to increase the gain of the screen at the screen edge, so that a viewer does not notice a lack of brightness uniformity across the screen.
However, a Fresnel lens typically generates a ghost image, which is the result of internal reflections within the lens and the substrate to which the lens may be attached. The ghost image may be perceived by the viewer, with the effect that the image quality is reduced and the viewer may be distracted. Consequently, the screen manufacturer has to compromise between brightness uniformity and image quality.
Therefore, there is a need for a Fresnel collimating lens, for use with a projection screen, that reduces, or avoids, the production of ghost images. The Fresnel collimating lens should also maintain the capability of effectively collimating light to provide more uniform brightness across the screen.
SUMMARY OF THE INVENTION
Generally, the present invention relates to a screen having a Fresnel lens laminated to another layer for support.
In one embodiment of the invention, a screen includes a Fresnel lens having an output surface, and a dispersing screen supportingly attached on a first side to the output surface of the Fresnel lens. In another embodiment of the invention, a screen includes a Fresnel lens having an output surface, where at least a portion of the output surface includes a Fresnel structure. A first optical layer has a first surface supportingly attached to the output Fresnel structured surface of the Fresnel lens. In another embodiment of the invention, a first layer has a first surface, and a redirecting means for redirecting light passing through the screen, has a Fresnel structured output surface. Attaching means on at least one of the first layer and the redirecting means supportingly attaches the output surface of the redirecting means to the first surface of the first layer. In another embodiment of the invention, a layer of transparent material has an input surface and a Fresnel-structured output surface having ridges formed between functional slopes and riser slopes, at least some of the ridges being truncated with flat portions essentially parallel to the input surface. In another embodiment of the invention, a layer of transparent material has an output surface with a Fresnel-structured portion proximate an edge thereof and a substantially unstructured center portion. In another embodiment of the invention, a first layer has a first surface, and a Fresnel lens having a Fresnel-structured output surface. The Fresnel-structured output surface includes functional slopes and riser slopes, and at least a portion of one functional slope and a portion of a riser slope are embedded in the first surface of the first layer.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.
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Hennen Daniel W.
Moshrefzadeh Robert S.
Nelson John C.
Tapio Scott M.
Thomas Patrick A.
3M Innovative Properties Company
Mahoney Christopher
Miller William D.
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