RETROVIEWER

• US 3,767,291 A
• Filed: 03/31/1972
• Issued: 10/23/1973
• Est. Priority Date: 03/31/1972
• Status: Expired due to Term

• Current Assignee: Edgar G. Johnson
• Original Assignee: Edgar G. Johnson
• Inventors: Johnson, Edgar G.
• Primary Examiner(s): Schonberg, David
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/240,132
• Time in Patent Office: 571 Days
• Field of Search: 350/3.5,13,103,235-239,245,211
• US Class Current: 380/54
• CPC Class Codes: G02B 27/025 and magnifying means

Abstract

A retroviewer for use in verifying a document having a retroreflective image bearing layer which is substantially transparent under ordinary diffuse light viewing conditions to provide viewing of images on an underlying surface. The viewer includes a lamp and a condensing lens mounted in a housing and in combination producing a virtual image of the light source that has an area between 0.5 sq. in. and 3 sq. in. A beam splitter is inclined to the optical axis of the lamp and condenser lens combination and it is positioned to reflect a portion of the light transmitted by the lens onto a viewing stage which supports a document to be verified. Light reflected from the beam splitter is retro-reflected from the image bearing layer of the document and a portion thereof is transmitted through the beam splitter for viewing to verify the document by its retro-reflective image.

Claims

1. A retroviewer for use in verifying a document having a retroreflective image bearing layer which is substantially transparent under diffuse light viewing conditions, comprising:

a housing, a lamp mounted in said housing to provide a light source, a condensing lens positioned to collect and transmit light from said lamp, a viewing stage for supporting a said document to be verified, a beam splitter inclined to the optical axis of said lamp and lens and positioned to reflect onto said viewing stage a portion of the light transmitted by said lens and to transmit a portion of any light retro-reflected from a said document on said stage, said lamp and said condensing lens combining to produce a virtual image of the light source that has an area between 0.5 sq. in. and 3 sq. in.

2. A retroviewer as recited in claim 1 wherein said lamp and said condensing lens combine to produce a virtual image of the light source that is between 0.8 sq. in. and 2 sq. in.

3. A retroviewer as recited in claim 1 wherein said lamp and said condensing lens combine to produce a virtual image of the light source that is spaced from said viewing stage a distance of from 14 to 18 inches.

4. A retroviewer as recited in claim 1 wherein said condensing lens has a focal length less than 5 in.

5. A retroviewer as recited in claim 1 wherein said lamp has a filament defining said light source said lamp being positioned with the longest dimension of said filament perpendicular to the optical axis of said lamp and lens to illuminate a rectangular area on said viewing stage.

6. A retroviewer for use in verifying a document having a retro-reflective image bearing layer which is substantially transparent under diffuse light viewing conditions, comprising:

a housing, a lamp mounted in said housing to provide a light source, a condensing lens positioned to collect and transmit light from said lamp, a viewing stage for supporting a said document to be verified, a beam splitter inclined to the optical axis of said lamp and lens and positioned to reflect onto said viewing stage a portion of the light transmitted by said lens and to transmit a portion of any light retro-reflected from a said document on said stage, said lamp and said condensing lens combining to produce a virtual image of the light source sufficiently large that the line of sight to each part of a predetermined document area on said viewing stage passes through the retro-image of the virtual image of the light source over a range of distances from said viewing stage along the optical viewing axis from at least 25 percent of the retro-image to viewing stage distance below the retro-image to at least 50 percent of the retro-image to viewing stage distance above the retro-image and sufficiently small that the retro-luminance of the retro-reflective layer of a properly validated document is high enough to obscure any images underlying the retro-reflective layer.

7. A retroviewer for use in verifying a document having a retro-reflective image bearing layer which is substantially transparent under diffuse light viewing conditions, comprising:

a housing, a lamp mounted in said housing to provide a light source, a condensing lens positioned to collect and transmit light from said lamp, a viewing stage for supporting a said document to be verified, a beam splitter inclined to the optical axis of said lamp and lens and positioned to reflect onto said viewing stage a portion of the light transmitted by said lens and to transmit a portion of any light retro-reflected from a said document on said stage, said lamp and said condensing lens combining to produce a virtual image of the light source sufficiently large that the line of sight to all parts of a predetermined document area on said viewing stage pass through the retro-image of the virtual image of the light source over a range of distances along the optical viewing axis of at least ten inches and sufficiently small that the retro-luminance of the retro-reflective layer of a properly validated document is high enough to obscure any images underlying said retro-reflective layer.