Color corrected projection lens

• US RE35,310 E
• Filed: 10/15/1992
• Issued: 08/06/1996
• Est. Priority Date: 09/05/1989
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: US Precision Lens, Inc. (3M Company)
• Inventors: Moskovich, Jacob
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Phan, James
• Application Number:
  US07/961,510
• Time in Patent Office: 1,391 Days
• Field of Search: 359/648-651, 359/708, 359/713-716, 359/764, 359/784, 359/791, 359/754-756, 359/757, 359/763
• US Class Current: 359/649
• 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 9/12 having three components only

Abstract

A projection lens in which a lens unit which may comprise one or two elements is closely coupled at the object end of the lens to a cathode ray tube. At the image end is a lens unit of overall weak optical power which comprises from the image end a first positive element followed by a closely spaced negative element of substantially higher dispersion. Intermediate the object side lens unit and the image side lens unit is a lens unit of substantial optical power supplying substantially all of the positive optical power of the lens. Closely spaced to this power lens unit on the object side is a negative lens element of high dispersion. This negative lens element may be considered to be part of the power lens unit. The negative lens elements have weak optical power at the axis of the lens but are of generally increasing negative optical power from the optical axis to the clear apertures of the negative lens elements to contribute to proper color correction of the lens, particularly axial chromatic aberration adjacent the full aperture. The intermediate positive power lens unit may comprise one or two positive elements depending upon the application and the manner in which the power is to be distributed to minimize aberrations. A lens embodying the invention is capable of maintaining a high image quality over a large range of magnifications by moving the first and second lens units from the image end in predetermined differential relationship.

Claims

1. A projection lens for a cathode ray tube comprising a rear lens unit .[.adopted.]. .Iadd.adapted .Iaddend.to be closely coupled to a cathode ray tube at the object end thereof, said lens unit having a strongly concave image side surface,

a front lens unit on the image side of said lens .[.comprising.]. .Iadd.consisting of .Iaddend.a positive image side element having a dispersion similar to the dispersion of crown glass followed by a closely spaced negative element of high dispersion similar to the dispersion of flint glass, and

another lens unit providing substantially all of the positive optical power of said lens intermediate said front and rear lens units, said another lens unit including a negative element of high dispersion similar to the dispersion of flint glass on the object side thereof.

2. The lens of claim 1 where said another lens unit comprises two positive elements both having spherical surfaces.

3. The lens of claim 1 further including a corrector lens unit of weak optical power having at least one aspherical surface positioned between said rear lens unit and said another lens unit so that the axial marginal rays from the long conjugate side of said lens intersect said corrector lens unit below the clear aperture thereof.

4. The lens of claim 3 where said front lens unit and said another lens unit move in fixed relation and said rear lens unit together with said corrector lens unit move in fixed relation but differentially with respect to said front lens unit and said another lens unit to vary the focal length of said lens.

5. The lens of claim 1 where the absolute value of the optical power of said negative lens element of said front lens unit increases from the optical axis to the clear aperture thereof due to at least one aspheric surface thereof.

6. The lens of claim 1 where said lens elements of said front lens unit contribute to correction of axial chromatic aberration adjacent the clear aperture thereof.

7. The lens of claim 1 where the elements of said another lens unit contribute to correction of axial chromatic aberration adjacent the clear apertures thereof.

8. The lens of claim 1 where said negative lens element of said front lens unit changes in optical power with height from the optical axis of the lens to contribute to correction of axial chromatic aberration in combination with the power of the preceding positive element of said front lens group.

9. The lens of claim 1 where said front lens unit and said another lens unit move in the same direction but at differential rates to vary the focal length of said lens.

10. A projection lens for a cathode ray tube comprising from the image end,

a first positive lens element having at least one aspheric surface followed closely by a second negative lens element of high dispersion having at least one aspheric surface, a third strongly positive lens element followed by a fourth negative lens element having at least one aspheric surface, and a fifth negative lens unit having a strongly concave image side surface and adapted to be closely coupled to a cathode ray tube.

11. The lens of claim 10 further including another positive lens element closely adjacent said third lens element on the image side of said third lens element.

12. The lens of claim 10 further including a corrector lens unit of weak optical power having at least one aspherical surface positioned between said fourth lens element and said fifth negative lens unit so that the axial marginal rays from the long conjugate side of said lens intersect said corrector lens element below the clear aperture thereof.

13. The lens of claim 10 where the absolute value of the optical power of said second negative lens element increases from the optical axis to the clear aperture thereof due to said at least one aspheric surface thereof.

14. The lens of claim 10 where said first and second lens elements contribute to correction of axial chromatic aberration adjacent the clear apertures thereof.

15. The lens of claim 10 where said third and fourth lens elements contribute to correction of axial chromatic aberration adjacent the clear apertures thereof.

16. The lens of claim 10 where said negative lens elements change in absolute optical power with height from the axis of the lens to the clear aperture thereof due to the aspheric surfaces on each element.

17. A projection lens for a cathode ray tube comprising a first positive element having at least one aspheric surface, a second negative lens element closely spaced to said first element having at least one aspheric surface and being of stronger absolute optical power adjacent the clear aperture thereof than at the optical axis, said second element having a high dispersion similar to the dispersion of flint glass, said first lens element having a dispersion similar to the dispersion of crown glass, a third strongly positive lens element having a dispersion similar to the dispersion of crown glass, a fourth negative lens element closely spaced to said third lens element having a dispersion similar to the dispersion of flint glass, said fourth lens element having at least one aspheric surface which increases in absolute optical power from the optical axis to the clear aperture thereof, and a lens unit having a strongly concave image side surface adapted to be closely coupled to a cathode ray tube.

18. The lens of claim 17 further including another positive lens elements on the image side of said third lens element and closely spaced thereto.

19. The lens of claim 17 further including a corrector lens element of weak optical power having at least one aspheric surface positioned between said fourth lens element and said lens unit such that the axial marginal rays from the long conjugate side of said lens interact said corrector lens element below the clear aperture thereof.

20. The lens of claim 17 where said lens first and second elements contribute to correction of axial chromatic aberration adjacent the clear apertures thereof.

21. The lens of claim 17 where said third and fourth elements contribute to correction of axial chromatic aberration adjacent the clear apertures thereof.

22. The lens of claim 17 where said second and fourth negative lens elements change in absolute optical power with height from the axis of the lens to the clear aperture thereof due to at least one aspheric surface on each element.

23. A projection lens for a cathode ray tube comprising from the long conjugate side a first lens unit of weak power, including a positive element followed by a closely spaced negative element having at least one aspherical surface and made out of material with higher dispersion than said positive element;

a second lens unit providing most of the positive power of the lens and including at least one positive element followed by a closely spaced negative element having higher dispersion than the preceding positive element; and

a third lens unit of negative power and including a strong negative element in the vicinity of a cathode ray tube.

24. The lens of claim 23 where said second lens unit comprises two positive elements.

25. The lens of claim 23 further including a corrector lens element positioned between said second and said third lens units, said corrector element having at least one aspherical surface.

26. The lens of claim 23 where the optical power of the negative lens element in said first lens unit changes from the optical axis to the clear aperture thereof.

27. The lens of claim 23 where the optical power of the negative lens element in said second lens unit gradually changes from the optical axis to the clear aperture thereof.

28. The lens of claim 23 where said positive and negative lens elements of said first and second units contribute to correction of axial chromatic aberration adjacent the clear aperture thereof.

29. A projection lens for a cathode ray tube comprising from the long conjugate a first positive lens element having at least one aspherical surface followed closely by a second negative lens element of high dispersion having at least one aspherical surface, a third strongly positive lens element followed by a fourth negative lens element of high dispersion having at least one aspherical surface, and a fifth strongly negative lens component having a strongly concave image side surface.

30. The lens of claim 29 further including another positive lens element closely adjacent said third lens element.

31. The lens of claim 29 further including a corrector lens element having at least one aspherical surface positioned between said fourth lens element and said fifth strongly negative component adjacent to a cathode ray tube so that the axial marginal rays from the long conjugate side of said lens intersect said corrector lens element below the clear aperture thereof.

32. The lens of claim 29 where said negative lens elements change in power with height from the axis of the lens to the clear aperture thereof due to at least one aspherical surface on each element.

33. The lens of claim 29 where said first and second elements contribute to correction of longitudinal chromatic aberration.

34. The lens of claim 29 where said third and fourth elements contribute to correction of longitudinal chromatic aberration.

35. A projection lens for a cathode ray tube comprising a first positive element having at least one aspheric surface, a second negative lens element closely spaced to said first element and having at least one aspheric surface and being of stronger absolute power adjacent the clear aperture thereof than at the optical axis, said second element having a high dispersion similar to the dispersion of flint glass, said first lens element having a dispersion similar to the dispersion of crown glass, a third strongly positive element with a dispersion similar to the dispersion of crown glass, a fourth negative lens element closely spaced to said third lens element having a dispersion similar to the dispersion of flint glass, said fourth lens element having at least one aspherical surface and being of stronger absolute power adjacent the clear aperture thereof than at the optical axis, and a fifth negative lens having a strongly concave surface facing the long conjugate side and adapted to be closely coupled to a cathode ray tube.

36. The lens of claim 35 further including another positive lens element on the long conjugate side of the third lens element and closely spaced thereto.

37. The lens of claim 35 further including a corrector lens element having at least one aspheric surface positioned between said fourth lens element and said fifth lens.

38. A projection lens for a cathode ray tube comprising from the long conjugate a first unit of a weak power and including at least one positive element of low dispersion and one negative element of high dispersion and having at least one aspherical surface;

a second lens unit providing most of the positive power of the lens and including at least one positive element of low dispersion and one negative element of high dispersion, a third lens unit of strong negative power adapted to be closely coupled to a cathode ray tube, said lens being capable of changing magnifications by moving said first and said second lens units along the optical axis in a predetermined manner relative to each other while keeping said third unit stationary relative to a cathode ray tube.

39. The lens of claim 38 further including a corrector lens unit having at least one aspherical surface and positioned between said second and said third lens units, said corrector lens unit being kept stationary with respect to said third unit while said first and second lens units are moved to change magnification.

40. The lens of claim 38 where said negative elements in said first and second lens units change in power with height from the axis of the lens to the clear aperture thereof to contribute to correction of axial chromatic aberration in combination with the power of the preceding element. .Iadd.

41. A projection lens for a cathode ray tube comprising from the long conjugate side:

(a) a first lens unit of weak power comprising first and second elements, the first element having a lower dispersion than the second element and the second element having at least one aspheric surface, said first and second elements having positive and negative powers, respectively, at least in the vicinity of their clear apertures which serve to correct the lens'"'"' axial chromatic aberration;

(b) a second lens unit providing most of the positive power of the lens comprising third and fourth elements, the third element having a lower dispersion than the fourth element and the fourth element having at least one aspheric surface, said third and fourth elements having positive and negative powers, respectively, at least in the vicinity of their clear apertures which serve to correct the lens'"'"' axial chromatic aberration; and

(c) a third lens unit of negative power adapted to be closely coupled to a cathode ray tube..Iaddend..Iadd.

42. A projection lens for a cathode ray tube comprising a rear lens unit adapted to be closely coupled to a cathode ray tube at the object end thereof, said lens unit having a strongly concave image side surface,

a front lens unit on the image side of said lens comprising a positive image side element having a dispersion similar to the dispersion of crown glass followed by a closely spaced negative element of high dispersion similar to the dispersion of flint glass, and

another lens unit providing substantially all of the positive optical power of said lens intermediate said front and rear lens units, said another lens unit including a negative element of high dispersion similar to the dispersion of flint glass on the object side thereof,

wherein the lens further includes a corrector lens unit of weak optical power having at least one aspherical surface positioned between said rear lens unit and said another lens unit so that the axial marginal rays from the long conjugate side of said lens intersect said corrector lens unit below the clear aperture thereof, and

said front lens unit and said another lens unit move in fixed relation and said rear lens unit together with said corrector lens unit moved in fixed relation but differentially with respect to said front lens unit and said another lens unit to vary the focal length of said lens..Iaddend..Iadd.43. A projection lens for a cathode ray tube comprising a rear lens unit adapted to be closely coupled to a cathode ray tube at the object end thereof, said lens unit having a strongly concave image side surface,

a front lens unit on the image side of said lens comprising a positive image side element having a dispersion similar to the dispersion of crown glass followed by a closely spaced negative element of high dispersion similar to the dispersion of flint glass, and

another lens unit providing substantially all of the positive optical power of said lens intermediate said front and rear lens units, said another lens unit including a negative element of high dispersion similar to the dispersion of flint glass on the object side thereof,

wherein the absolute value of the optical power of said negative lens element of said front lens unit increases from the optical axis to the clear aperture thereof due to at least one aspheric surface thereof..Iaddend..Iadd.44. A projection lens for a cathode ray tube comprising a rear lens unit adapted to be closely coupled to a cathode ray tube at the object end thereof, said lens unit having a strongly concave image side surface,

a front lens unit on the image side of said lens comprising a positive image side element having a dispersion similar to the dispersion of crown glass followed by a closely spaced negative element of high dispersion similar to the dispersion of flint glass, and

another lens unit providing substantially all of the positive optical power of said lens intermediate said front and rear lens units, said another lens unit including a negative element of high dispersion similar to the dispersion of flint glass on the object side thereof,

wherein said negative lens element of said front lens unit changes in optical power with height from the optical axis of the lens to contribute to correction of axial chromatic aberration in combination with the power of the preceding positive element of said front lens

43. unit..Iaddend..Iadd. . A projection lens for a cathode ray tube comprising a rear lens unit adapted to be closely coupled to a cathode ray tube at the object end thereof, said lens unit having a strongly concave image side surface,

a front lens unit on the image side of said lens comprising a positive image side element having a dispersion similar to the dispersion of crown glass followed by a closely spaced negative element of high dispersion similar to the dispersion of flint glass, and

another lens unit providing substantially all of the positive optical power of said lens intermediate said front and rear lens units, said another lens unit including a negative element of high dispersion similar to the dispersion of flint glass on the object side thereof,

wherein said front lens unit and said another lens unit move in the same direction but at differential rates to vary the focal length of said lens..Iaddend.