Projection lens incorporating a pair of matching plastic lenses

• US 5,371,628 A
• Filed: 05/20/1993
• Issued: 12/06/1994
• Est. Priority Date: 05/27/1992
• Status: Expired due to Fees

• Current Assignee: Sekinos Company Limited
• Original Assignee: Sekinos Company Limited
• Inventors: Sekine, Kumajiro, Shimoda, Yoshihisa
• Primary Examiner(s): Sugarman, Scott J.
• Application Number:
  US08/063,700
• Time in Patent Office: 565 Days
• Field of Search: 359/749, 359/750, 359/713, 359/714
• 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 9/60 having five components only

Abstract

This projection lens for a projection television includes coaxially in order towards the face plate of the CRT: a first lens of negative power, both of whose surfaces are aspherical; a second lens of positive power, at least one of whose surfaces is aspherical, formed of a plastic material; a third lens of positive power; a fourth lens of positive power, at least one of whose surfaces is aspherical, formed of a plastic material; and a back lens of negative power, which presents in the direction away from the face plate of the CRT a face of strongly concave curvature. The third lens is the strongest of the lenses in absolute power, and the second lens and the fourth lens have substantially the same optical characteristics, and are disposed in reverse orientation on opposite sides of the third lens. Certain conditions relating to lens parameters should be satisfied for acceptable optical performance. It is anticipated that the second lens and the fourth lens will be manufactured from plastic material by using the same metal mold for injection molding, which provides highly desirable cost economy for manufacturing setup.

Claims

1. A projection lens for a projection television comprising a CRT which comprises a face plate, comprising coaxially in order in the direction towards said face plate of said CRT:

a first lens of negative power, both of whose surfaces are aspherical, and formed of a plastic material;

a second lens of positive power, at least one of whose surfaces is aspherical;

a third lens of positive power;

a fourth lens of positive power, at least one of whose surfaces is aspherical, and formed of a plastic material;

a fifth lens both of whose surfaces are aspherical, having substantially the same optical characteristics as said first lens;

and a back lens of negative power, which presents in the direction away from said face plate of said CRT a face of strongly concave curvature;

said third lens being the strongest in absolute power of said six lenses; and

;

said second lens and said fourth lens having substantially the same optical characteristics, and being disposed in reverse orientation on opposite sides of said third lens;

wherein the following conditions are satisfied;

(1) 0.03<

|f₂ /f₁ |<

0.6;

(2) 1.0<

f₃ /f<

1.4;

(3) D₂ /f<

0.07; and

;

(4) 2<

E₁ /D₁ <

4

in which;

f is the overall focal length of the entire system;

f_i is the focal length of the ith one of said lenses;

D₁ is the central thickness of said first lens;

D₂ is the axial distance between the opposing surfaces of said first lens and said second lens; and

;

E₁ is the distance between the two surfaces of said first lens along the edges of the ray furthest from the optical axis.

2. A projection lens according to claim 1, wherein said third lens is formed of a glass material.

3. A projection lens according to claim 1, wherein said third lens is formed of a glass material.

4. A projection lens according to claim 1, wherein said second lens and said fourth lens are substantially identical in form and material.

5. A projection lens according to claim 2, wherein said second lens and said fourth lens are substantially identical in form and material.

6. A projection lens according to claim 3 wherein said second lens and said fourth lens are substantially identical in form and material.

7. A projection lens for a projection television comprising a CRT which comprises a face plate, comprising coaxially in order in the direction towards said face plate of said CRT:

a first lens of negative power, both of whose surfaces are aspherical, and formed of a plastic material;

a second lens of positive power, at least one of whose surfaces is aspherical, and formed of a plastic material;

a third lens of positive power;

a fourth lens of positive power, at least one of whose surfaces is aspherical, and formed of a plastic material;

and a back lens of negative power, which presents in the direction away from said face plate of said CRT a face of strongly concave curvature;

said third lens being the strongest in absolute power of said five lenses; and

said second lens and said fourth lens having substantially the same optical characteristics, and being disposed in reverse orientation on opposite sides of said third lens;

wherein the following conditions are satisfied;

(1) 0.03<

|f₂ /f₁ |<

0.6;

(2) 1.0<

f₃ /f<

1.4;

(3) D₂ /f<

0.07; and

;

(4) 2<

E₁ /D₁ <

4

in which;

f is the overall focal length of the entire system;

f_i is the focal length of the ith one of said lenses;

D₁ is the central thickness of said first lens;

D₂ is the axial distance between the opposing surfaces of said first lens and said second lens; and

;

E₁ is the distance between the two surfaces of said first lens along the edges of the ray furthest from the optical axis.

8. A projection lens according to claim 7, wherein one of said first lens and said second lens is formed of substantially the same material as one of said fourth lens and said back lens.

9. A projection lens according to claim 8, wherein said third lens is formed of a glass material.

10. A projection lens according to claim 7, wherein said second lens and said fourth lens are substantially identical in form and material.

11. A projection lens according to claim 10, wherein one of said first lens and said second lens is formed of substantially the same material as one of said fourth lens and said back lens.

12. A projection lens according to claim 11, wherein said third lens is formed of a glass material.

13. A projection lens according to claim 7, wherein said third lens is formed of a glass material.

14. A projection lens according to claim 8, wherein said third lens is formed of a glass material.

15. A projection lens according to claim 9, wherein said third lens is formed of a glass material.

16. A projection lens according to claim 10, wherein said third lens is formed of a glass material.

17. A projection lens according to claim 11, wherein said third lens is formed of a glass material.

18. A projection lens according to claim 12, wherein said third lens is formed of a glass material.