Objective lens system with aspheric Fresnel elements

• US 4,293,196 A
• Filed: 08/13/1979
• Issued: 10/06/1981
• Est. Priority Date: 08/13/1979
• Status: Expired due to Term

• Current Assignee: Fantacia
• Original Assignee: Fantacia
• Inventors: Hilbert, Robert S.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Sugarman, Scott J.
• Application Number:
  US06/065,994
• Time in Patent Office: 785 Days
• Field of Search: 350/211, 350/125 NG, 350/189, 350/409, 350/432, 350/452, 358/239
• US Class Current: 359/743
• CPC Class Codes: G02B 13/08 Anamorphotic objectives
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876

Abstract

A high speed projection lens system particularly adaptable for a television projection system having a viewing screen and a video image forming surface is provided. The projection lens system includes a first thin meniscus lens element convex to the projection screen having an aspherical Fresnel type surface; a second thin meniscus lens element concave to the projection screen having an aspherical Fresnel type surface and a weak third thin aspherical meniscus lens element.

Claims

1. A high speed objective lens system capable of forming images that is particularly adaptable for a television projection system comprising from a viewing screen object side to a video image side on an optical axis;

a first thin meniscus lens element convex to the object side having a curvilinear configuration on one side and a Fresnel type surface on the other side;

a second thin meniscus lens element concave to the object side having a curvilinear configuration on one side and a Fresnel type surface on the other side, and

a third weak thin aspherical meniscus lens element convex to the object side.

2. The invention of claim 1 wherein each of the Fresnel surfaces have a locus of median points of their respective step facets that form a nonplanar configuration.

3. The invention of claim 1 wherein the object side of the third lens includes an aspherical surface.

4. The invention of claim 1 wherein the third lens has one surface having a curvilinear configuration on one side and a Fresnel type surface on the other side.

5. The invention of claim 1 wherein the effective diameter of each lens is at least twenty times greater than its maximum thickness.

6. The invention of claim 1 wherein the slopes of step facets forming the Fresnel surfaces are aspherical.

7. The invention of claim 1 wherein each lens element has the same thickness on the optical axis.

8. The invention of claim 1 wherein each lens is formed from a plastic material.

9. The invention of claim 8 wherein each lens is formed from an acrylic plastic.

10. The invention of claim 1 wherein the speed of the lens system is greater than or equal to F/1.9.

11. In a video projection system having a projection screen and an image forming surface, the improvement comprising;

a high speed objective projection lens assembly operatively positioned relative to the image forming surface for projecting the images onto the screen including a first thin meniscus lens element convex to the projection screen, a second thin meniscus lens element concave to the projection screen, and a third thin lens element, at least one surface on each of two lens elements have a Fresnel type surface, the locus of median points of respective step facets of each Fresnel type surface forming a nonplanar configuration.

12. The invention of claim 11 wherein the slopes of the step facets of the Fresnel surface are aspherical.

13. The invention of claim 11 wherein each of the meniscus lens elements have one aspherical Fresnel facet surface.

14. The invention of claim 11 wherein the effective diameter of each lens is at least twenty times greater than its maximum thickness.

15. The invention of claim 11 wherein each lens element has the same thickness on the optical axis.

16. The invention of claim 11 wherein each lens is formed from a plastic material.

17. The invention of claim 11 wherein the speed of the lens system is greater than or equal to F/1.9.

18. The invention of claim 16 wherein each lens is formed from an acrylic plastic.

19. A high speed plastic objective lens system comprising from image to object side;

a first thin meniscus lens element convex to the image side;

a second thin meniscus lens element concave to the image side;

a third thin lens element, at least one surface on each of two lens elements have a Fresnel surface, the locus of median points of respective step facets of each Fresnel surface forming a nonplanar configuration.

20. The invention of claim 19 wherein the locus of median points traces a cross-sectional circular path.

21. The invention of claim 19 wherein the slopes of step facets forming each Fresnel surface is aspherical.

22. The invention of claim 19 wherein the lens element is molded from a plastic material.

23. The invention of claim 19 wherein the object side surface of the third lens element is convex to the image side.

24. The invention of claim 19 wherein the effective diameter of each lens is at least twenty times greater than its maximum thickness.

25. The invention of claim 24 wherein each Fresnel refracting surface is aspherical.

26. The invention of claim 25 wherein at least one refracting surface on each lens element is aspherical.

27. The invention of claim 25 wherein the speed of the lens system is at least F/1.9.

28. The invention of claim 25 wherein the locus of the median points has a base radius, RB, which is within a range of 0.53 to 20 times the diameter of the lens elements with the Fresnel refracting surface.

29. A high speed plastic objective lens system comprising the following design parameters;

space="preserve" listing-type="tabular">__________________________________________________________________________ELEMENT R1 R2 T N/V __________________________________________________________________________OBJECT DISTANCE 57.4401 L.sub.1 A(1) 5.3957 0.900 1.491/57.2 RB.sub.1 = 6.685 2.8223 APERTURE STOP 2.5535 L.sub.2 A(2) RB.sub.2 = -2.6328 -2.7674 .0900 1.491/57.2 .8591 L.sub.3 A(3) RB.sub.3 = 21.744 13.2925 .0900 1.491/57.2 IMAGE 8.0552 ASPHERIC CONSTANTS ##STR4## ASPHERIC CURVATURE K A B __________________________________________________________________________A(1) .28380247 0.000000 -9.31229E -4 -5.36759E -4 A(2) -.12935331 0.000000 -1.85253E -2 7.55302E -4 A(3) -.03567578 0.000000 1.44629E -2 -1.63779E -3 __________________________________________________________________________ C D __________________________________________________________________________ 6.38404E -5 -5.05445E -6 5.339075E -5 -2.961245E -5 1.11646E -4 -3.29334E -6 __________________________________________________________________________

30. A high speed plastic objective lens system comprising the following design parameters;

space="preserve" listing-type="tabular">__________________________________________________________________________ELEMENT R1 R2 T N/V __________________________________________________________________________OBJECT DISTANCE 57.4401 L.sub.1 A(1) 5.3957 0.900 1.491/57.2 RB.sub.1 = 6.685 2.8223 APERTURE STOP 2.5535 L.sub.2 A(2) RB.sub.2 = -2.6328 -2.7674 .0900 1.491/51.2 .8591 L.sub.3 A(3) RB.sub.3 = 21.744 13.2925 .0900 1.491/57.2 IMAGE 8.0552 ASPHERIC CONSTANTS ##STR5## __________________________________________________________________________ASPHERIC CURVATURE K A B __________________________________________________________________________A(1) .28380247 0.000000 -9.31229E -4 -5.36759E -4 A(2) -.12935331 0.000000 -1.85253E -2 7.55302E -4 A(3) -.03580302 0.000000 1.46732E -2 -1.67730E -3 __________________________________________________________________________ C D __________________________________________________________________________ 6.38404E -5 -5.05445E -6 5.33907E -5 -2.96124E -5 1.12721E -4 -3.22124E -6 __________________________________________________________________________

31. A high speed plastic objective lens system comprising the following design parameters;

space="preserve" listing-type="tabular">__________________________________________________________________________ELEMENT R1 R2 T N/V __________________________________________________________________________OBJECT DISTANCE 73.5468 L.sub.1 A(1) 13.5990 0.900 1.491/57.2 RB.sub.1 = 16.474 4.9097 APERTURE STOP 4.6420 L.sub.2 A(2) -4.1397 .0900 1.491/57.2 RB.sub.2 = -3.784 1.1783 L.sub.3 A(3) 26.0000 .0900 1.491/57.2 RB.sub.3 = 34.846 IMAGE 8.2004 ASPHERIC CONSTANTS ##STR6## ASPHERIC CURVATURE K A B __________________________________________________________________________A(1) .17086590 0.000000 -3.65390E -4 -2.22403E -5 A(2) -.07207025 0.000000 -7.02038E -3 +2.17572E -4 A(3) -.04295470 0.000000 5.87983E -3 -3.05549E -4 __________________________________________________________________________ C D __________________________________________________________________________ 6.51163E -7 -2.70110E -8 -5.84082E -6 -6.19676E -7 9.46927E -6 -1.24323E -7 __________________________________________________________________________