Compact projection lens

• US 4,526,442 A
• Filed: 07/06/1981
• Issued: 07/02/1985
• Est. Priority Date: 01/28/1981
• Status: Expired due to Term

• Current Assignee: US Precision Lens Incorporated 3997 Mcmann Road 45245
• Original Assignee: US Precision Lens, Inc.
• Inventors: Betensky, Ellis I.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Sugarman, Scott J.
• Application Number:
  US06/280,785
• Time in Patent Office: 1,457 Days
• Field of Search: 350/412, 350/445, 350/474, 350/477, 350/432-435
• US Class Current: 359/651
• CPC Class Codes: G02B 13/16 for use in conjunction with image converters or intensifiers , or for use with projectors, e.g. objectives for projection TV
• CPC Class Codes: G02B 13/18 with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration G02B13/002 takes precedence
• CPC Class Codes: G02B 9/16 all the components being simple

Abstract

A compact projection lens for a cathode ray tube comprises from the image end, a first group of positive power which corrects aperture dependent aberrations, a second positive group and a third group which corrects for field curvature and distortion. A mirror is inserted between the first and second groups to fold the optical axis.

Claims

1. A projection lens for a cathode ray tube display, said lens consisting of three groups from the image end to the object end, as follows:

a first group comprising an element of relatively weak optical power having at last one aspheric surface;

a second positive group air spaced from said first group providing substantially all the positive power of said lens;

a third group air spaced from said second group and comprising a negative element having a surface concave to the image end and serving as a field flattener essentially correcting the Petzval curvature of the first and second groups;

wherein said three groups have optical powers K1, K2, and K3, the overall lens has an optical power of 1.0, and

3. A lens according to claim 1 having aspheric surfaces wherein each aspheric lens surface is defined by the following relationship:

##EQU2## where X is the surface sag at a semi-aperture distance y from the optical axis of the lens, C is the curvature of the lens surface of the optical axis A equal to the reciprocal of the radius of the lens at the optical axis, k is a conic constant, D, E, F, and G are constants.

8. A lens as defined in claims 1 or 6, wherein the concave surface is aspheric.

10. The lens of claim 8 where the image and object side surfaces of said second group are bi-convex.

11. The lens of claim 8 where said concave surface of said element of said third group is aspheric.

12. The lens of claim 8 where

13. The lens of claim 8 where said first group consists of a single element.

15. The lens of claim 13 where said first and second groups are air spaced a substantial percentage of the equivalent focal length of said lens.

16. The lens of claim 13 where said first and second groups are air spaced more than 0.9 of the equivalent focal length of said lens.

17. The lens of claim 13 where said second group consists of a biconvex element.

18. The lens of claim 13 where said first group consists of a single element.

20. The lens of claim 18 where said first and second groups are air spaced a substantial percentage of the equivalent focal length of said lens.

21. The lens of claim 18 where the air spacing between said first and second groups is at least 0.9 of the equivalent focal length of said lens.

22. The lens of claim 18 where said second group has biconvex object and image side surfaces.

23. The lens of claim 18 where said second group has biconvex image and object side surfaces.

24. The lens of claim 22 where said second group comprises a single element.

26. The lens of claim 24 where said first and second groups are air spaced a substantial percentage of the equivalent focal length of said lens.

27. The lens of claim 24 where the air spacing between said first and second groups is at least 0.9 of the equivalent focal length of said lens.

28. The lens of claim 24 where said second group consists of a single element.

2. 25<

K1<

0.50,

space="preserve" listing-type="equation">0.85<

K2<

1.20,

space="preserve" listing-type="equation">-1.4<

K3<

-0.9

4. A lens according to claim 2 scaled to an EFL of 116.5 mm and relative aperture of f/1.0 described substantially as follows:

space="preserve" listing-type="tabular">______________________________________ Surface Axial Distance Radius (mm) Between Surfaces (mm) N.sub.d V.sub.d______________________________________ S1 201.04L1 16.00 1.492 57.1 S2 -6569.50 114.00 S3 68.36L2 32.50 1.492 57.1 S4 -198.13 57.58 S5 -43.66L3 3.00 1.492 57.1 S6 -5397.88 6.00______________________________________Aspheric surfaces;

S1, S4, S5 S1 S4 S5______________________________________D -.1316 ×

10.sup.-6 .3056 ×

10.sup.-6 -.6240 ×

10.sup.-5E .8734 ×

10.sup.-11 .6813 ×

10.sup.-10 .1576 ×

10.sup.-8F -.2910 ×

10.sup.-14 -.4657 ×

10.sup.-13 .3861 ×

10.sup.-12G .1959 ×

10.sup.-18 .8216 ×

10.sup.-17 -.4809 ×

10.sup.-15C 1.326 -5.183 -5.599______________________________________

Where L1-L3 are successive lens elements from the image end, S1-S6 are successive element surfaces, the surface radii where positive are surfaces convex to the image end and where negative are concave to the image end, N_d is the index of refraction of the lens elements, V_d is the dispersion of the lens elements measured by the Abbe number, and surfaces S1, S4, and S5 are aspheric.

5. A lens according to claim 2 scaled to an EFL of 117.4 mm and relative aperture of f/1.0 is described substantially as follows:

space="preserve" listing-type="tabular">______________________________________ Surface Axial Distance Radius (mm) Between Surfaces (mm) N.sub.d V.sub.d______________________________________ S1 167.81Ll 16.00 1.492 57.1 S2 1230.59 114.00 S3 68.56L2 30.69 1.492 57.1 S4 -207.25 58.65 S5 -47.89L3 3.00 1.492 57.1 S6 6.00______________________________________Aspheric surfaces;

S2, S4, S5 S2 S4 S5______________________________________D .1194 ×

10.sup.-6 .3971 ×

10.sup.-6 .1488 ×

10.sup.-5E -.1066 ×

10.sup.-10 .2482 ×

10.sup.-10 -.1112 ×

10.sup.-8F .2273 ×

10.sup.-14 -.2710 ×

10.sup.-13 .1395 ×

10.sup.-11G -.7673 ×

10.sup.-19 .4807 ×

10.sup.-17 -.6276 ×

10.sup.-15C -1.000 -1.000 -1.000______________________________________

Where L1-L3 are successive lens elements from the image end, S1-S6 are successive element surfaces, the surface radii where positive are surfaces convex to the image end and where negative are concave to the image end, N_d is the index of refraction of the lens elements, V_d is the dispersion of the lens elements measured by the Abbe number, and surfaces S2, S4 and S5 are aspheric.

6. A lens according to claim 2 scaled to an EFL of 116.6 mm and relative aperture of f/1.0 is described substantially as follows:

space="preserve" listing-type="tabular">__________________________________________________________________________ Surface Axial Distance Radius (mm) Between Surfaces (mm) N.sub.d V.sub.d__________________________________________________________________________ S1 201.71L1 16.00 1.492 57.1 S2 114.00 S3 68.84L2 32.50 1.492 57.1 S4 -196.58 58.85 S5 -44.84L3 3.00 1.492 57.1 S6 6.00__________________________________________________________________________Aspheric surfaces;

S1, S3, S4, and S5 S1 S3 S4 S5__________________________________________________________________________D -.1284 ×

10.sup.-6 -.2543 ×

10.sup.-7 .2749 ×

10.sup.-6 -.5975 ×

10.sup.-5E .7793 ×

10.sup.-11 .2858 ×

10.sup.-11 .7423 ×

10.sup.-10 .1478 ×

10.sup.-8F -.2784 ×

10.sup.-14 -.4865 ×

10.sup.-16 -.4456 ×

10.sup.-13 .3204 ×

10.sup.-12G .1840 ×

10.sup.-18 -.1098 ×

10.sup.-18 .7464 ×

10.sup.-17 -.4199 ×

10.sup.-15C 1.326 .0001 -5.183 -5.599__________________________________________________________________________

Where L1-L3 are successive lens elements from the image end, S1-S6 are successive element surfaces, the surface radii where positive are surfaces convex to the image end and where negative are concave to the image end N_d is the index of refraction of the lens elements, V_d is the dispersion of the lens elements measured by the Abbe number, and surfaces S1, S3, S4, and S5 are aspheric.

7. A projection lens for a cathode ray tube display, said lens consisting of three groups from the image end to the object end, as follows:

a first group comprising an element of relatively weak optical power having an aspheric surface and serving to correct aperture dependent aberrations;

a second positive group air spaced from said first group and providing substantially all the positive power of said lens and comprising a biconvex element;

a third group air spaced from said second group and comprising a negative element having an image side surface concave to the image end of strong negative power and a substantially plano object side surface, said third group essentially correcting the Petzval curvature of said first and second groups;

said three groups have optical powers K1, K2, and K3, the overall lens has an optical power of 1.0, and

space="preserve" listing-type="equation">0.25<

K1<

0.50,

space="preserve" listing-type="equation">0.85<

K2<

1.20,

space="preserve" listing-type="equation">-1.40<

K3<

-0.9

9. A projection lens for a cathode ray tube display consisting from the image end of three groups as follows:

a first group of relatively weak optical power comprising an element having at least one aspheric surface and serving primarily to correct aperture dependent aberrations,

a second positive group air spaced from said first group providing substantially all of the positive power of said lens, and

a third negative group air spaced from said second group comprising an element having a concave image side surface and serving as a field flattener essentially correcting the Petzval curvature of the elements of said first and second groups,

said lens having an optical power of 1.0 and

space="preserve" listing-type="equation">0.85<

K.sub.2 <

1.20

space="preserve" listing-type="equation">-1.4<

K.sub.3 <

-0.9

where K₂ and K₃ are the optical powers of said second and third groups, respectively.

14. A projection lens for a cathode ray tube display consisting of three optical groups, said groups from the image end comprising a first group serving to correct aperture dependent aberrations, said first group having at least one aspheric surface, a second group of strong positive power air spaced from said first group and having biconvex object and image side surfaces, and a third group of negative optical power having an aspheric surface concave to the image end and air spaced from said second group, said third group serving as a field flattener and essentially correcting the Petzval curvature of the elements of said first and second groups, said lens having an optical power of 1.0 and

19. A projection lens for a cathode ray tube display consisting of three optical groups, said groups from the image end comprising a first group serving to correct aperture dependent aberrations, said first group consisting of a single element having at least one aspheric surface, a second group of strong positive power air spaced from said first group and a third group of negative optical power having an aspheric surface concave to the image end and air spaced from said second group, said third group serving as a field flattener and essentially correcting the Petzval curvature of the elements of said first and second groups, said lens having an optical power of 1.0 and

25. A projection lens for a cathode ray tube display consisting of three optical groups, said groups from the image end comprising a first group serving to correct aperture dependent aberrations, said first group consisting of a single element, a second group of strong positive power air spaced from said first group and having biconvex object and image side surfaces, said second group being of substantially greater optical power than said first group, and a third group of negative optical power having a surface concave to the image end and air spaced from said second group and serving as a field flattener and essentially correcting the Petzval curvature of the elements of said first and second groups, said lens having an optical power of 1.0 and