Projection lens system

• US 5,130,850 A
• Filed: 12/13/1990
• Issued: 07/14/1992
• Est. Priority Date: 12/20/1989
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Toide, Eiichi
• Primary Examiner(s): Sugarman, Scott J.
• Application Number:
  US07/627,190
• Time in Patent Office: 579 Days
• Field of Search: 350/412, 350/432-435, 359/649, 359/708
• US Class Current: 359/649
• 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

Abstract

A projection lens system for use in a projection type display and for displaying an image formed on a face plate of a cathode ray tube on a screen. The projection lens system includes of eight lens components disposed at the optical axis. The second and seventh lenses from the image side, among the eight lens components essentially have somewhat weak optical power, and are made up of a plastic lens having aspheric surfaces on both sides.

Claims

1. A projection lens system for displaying an image formed on a face panel of a cathode ray tube (CRT) on a screen and including a plurality of lens components disposed at an optical axis and arranged in a series, said projection lens system comprising:

(a) a first lens component disposed at an image end of said series of projection lenses having a positive power, and formed of a meniscus shape having a surface convex to the image;

(b) a second lens component disposed between said first lens component and said face panel, having a positive power in total, and formed of an overall meniscus shape, having at least one aspheric surface and having a surface convex to the image;

(c) a third lens component disposed between said second lens component and said face panel, and having a negative power;

(d) a fourth lens component disposed between said third lens component and said face panel, having a positive power, and formed of a bi-convex shape;

(e) a fifth lens component disposed between said fourth lens component and said face panel, being brought in contact with a surface of said fourth lens component facing said CRT, and having a negative power;

(f) a sixth lens component disposed between said fifth lens component and said face panel, having a positive power, and formed of a bi-convex shape;

(g) a seventh lens component disposed between said sixth lens component and said face plate, having a positive power in total, and formed in an overall meniscus-shape having at least one aspheric surface and a surface concave to the image; and

(h) an eight lens component disposed between said seventh lens component and said face plate, having a negative power, and formed of a plano-concave shape having a surface concave to the image.

2. A projection lens system according to claim 1, wherein each of said plurality of lens components satisfies the following relationships:

space="preserve" listing-type="equation">0.50<

f/f.sub.1 <

0.60

space="preserve" listing-type="equation">-0.65<

f/f.sub.3 <

-0.57

space="preserve" listing-type="equation">0.55<

f/f.sub.4+5 <

0.85

space="preserve" listing-type="equation">0.50<

f.sub.6 <

0.80

space="preserve" listing-type="equation">0.10<

d.sub.23 /f<

0.20

space="preserve" listing-type="equation">0.90<

d.sub.34 /d.sub.23 <

1.8

wherein f depicts a focal length of the overall projection lens;

f₁, depicts a focal length of said first lens component;

f₃, depicts a focal length of said third lens component;

f₄₊₅, depicts a focal length of a compound lens including said fourth lens component and said fifth lens component;

F₆, depicts a focal length of said sixth lens component;

d₂₃, depicts a distance between a lens surface of said second lens component and a lens surface of said third lens component; and

d₃₄, depicts a distance between a lens surface of said third lens component and a lens surface of said fourth lens component.

3. A projection lens system according to claim 2, wherein each of said lens components consists of a single lens element.

4. A projection lens system according to claim 3, wherein said second lens component and said seventh lens component have aspheric surfaces on both sides.

5. A projection lens system according to claim 4, wherein said second lens component and said seventh lens component are made up of plastic.

6. A projection lens system according to claim 5, wherein a lens surface of said second lens component has no inflection point.

7. A projection lens system according to claim 5, wherein said fifth lens component consists of bi-concave lens.

8. A projection lens system according to claim 7, wherein said third lens component consists of a meniscus lens having a surface convex to the image.

9. A projection lens system according to claim 5, wherein said fifth lens component consists of a meniscus lens having a surface concave to the image.

10. A projection lens system according to claim 9, wherein said third lens component consists of a bi-concave lens.

11. A projection lens system according to claim 9, wherein said third lens component consists of a meniscus lens having a surface convex to the image.

12. A projection lens system according to claim 9, wherein said third lens component consists of a plano-concave lens having a surface planar to the image.