# US 4,398,810 A · Fresnel lens system

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- Number: US 4,398,810 A
- Document ID: US4398810A
- Status: Granted
- Kind: A
- Application number: 06/350,001
- Filed: 1982-02-18
- Granted: 1983-08-16
- Earliest claimed: 1982-02-18
- Assignees: B Optical
- Inventors: Marvin P. Hodges; Richard A. Buchroeder
- Web page: https://patentgrep.com/patent/US4398810A

## CPC

- G02B 3/08: with discontinuous faces, e.g. Fresnel lens {(diffractive Fresnel lenses G02B5/1876)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A projection lens system of the type used in connection with cathode ray tubes, and more specifically a cathode ray tube projection system having an internal lens folding means, useful in projecting an image or series of images on a screen.

## Claims

### Claim 1

A Fresnel lens system having design parameters normalized for a 280 mm focal length represented by the following table:
______________________________________ Ele- Sepa- ment R D E F ration ______________________________________ A -364.848 +0.779 .times. -0.1990 .times. +0.2300 .times. mm 10.sup.-8 mm.sup.-3 10.sup.-12 mm.sup.-5 10.sup.-17 mm.sup.-7 280.6mm (nominal) B -269.834 +0.3539 .times. -0.118 .times. +0.5003 .times. mm 10.sup.-7 mm.sup.-3 10.sup.-11 mm.sup.-5 10.sup.-16 mm.sup.-7 119.8mm (nominal) C -142.473 +0.1322 .times. -0.6375 .times. +0.4502 .times. mm 10.sup.-7 mm.sup.-3 10.sup.-5 mm.sup.-5 10.sup.-17 mm.sup.-7 ______________________________________
wherein letters A through C identify the respective lens elements from the screen side to the cathode ray tube side and R, D, E, and F are constants of the following generating function:
x=y.sup.2 /2R+Dy.sup.4 +Ey.sup.6 +Fy.sup.8
where y is the zonal ray distance from the optical axis, and wherein and the slope of the generating function given as a tangent, is defined as:
tan .theta.=y/R+4Dy.sup.3 +6Ey.sup.5 +8Fy.sup.7
with all dimensions being expressed in millimeters, and wherein the design parameters may be normalized to any other focal length, lengths and lens materials.

### Claim 2 (depends on 1)

A Fresnel lens system as recited in claim 1 wherein said lens system is designed to protect an image from a convex image plane having a spherical curve of approximately 23 to 25 inches radius.

### Claim 3 (depends on 2)

A Fresnel lens system as recited in claim 2 wherein said image plane is the face plate of a cathode ray tube.

### Claim 4 (depends on 3)

A Fresnel lens system as recited in claim 3 wherein the cathode ray tube has approximately a 13 inch diagonal measure.

### Claim 5 (depends on 2)

A Fresnel lens system as recited in claim 2 wherein the radius of Element A is approximately 171 mm, the radius of Element B is approximately 110 mm, and the radius of Element C is approximately 171 mm.

### Claim 6 (depends on 5)

A Fresnel lens system as recited in claim 5 further including an aperture stop interposed between Element A and Element B.

### Claim 7 (depends on 6)

A Fresnel lens system as recited in claim 6 wherein said aperture stop has a diameter of approximately 152 millimeters and is spaced approximately 204 millimeters from Element A.

### Claim 8 (depends on 2)

A Fresnel lens system as recited in claim 2 further including a folding mirror disposed between Element A and Element B.

### Claim 9 (depends on 8)

A Fresnel lens system as recited in claim 8 wherein said folding mirror is spaced approximately 153 millimeters from Element A and disposed at approximately a 45 degree angle with respect to the optical axis.

### Claim 10 (depends on 9)

A Fresnel lens system as recited in claim 9 wherein said folding mirror operates as an aperture stop.

### Claim 11 (depends on 9)

A Fresnel lens system as recited in claim 9 wherein said convex image plane is tilted with respect to the optical axis.