Projection lens

• US 4,682,861 A
• Filed: 06/20/1985
• Issued: 07/28/1987
• Est. Priority Date: 06/25/1984
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Hosoya, Jun
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Gass, Rebecca D.
• Application Number:
  US06/747,029
• Time in Patent Office: 768 Days
• Field of Search: 350/432, 350/469
• US Class Current: 359/650
• 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 9/34 having four components only

Abstract

A projection lens for enlarging and projecting a television image on a screen including: a first lens L1 having a positive refracting power; a second lens L2 having a positive refracting power and a convex surface which is located at the side of L2 nearer to the image and which has a larger curvature than that at the side of L2 nearer to the screen; a third lens L3 which consists of a meniscus lens having a concave surface located at the side of L3 nearer to the image; and a fourth lens L4 having a concave surface which is located at the side of L4 nearer to the screen and which has a larger curvature than that at the side of L4 nearer to the image. The lenses L1, L2, L3 and L4 are arranged from the side of the screen in the order named. The combined refracting power of the second and third lenses is larger than that of the first lens. At least one nonspherical surface is provided in the first lens, and at least one nonspherical surface is provided in the second, third and fourth lenses.

Claims

1. A projection lens for projecting an image onto a screen, comprising:

a first lens having a positive refracting power;

a second lens having a positive refracting power and a convex surface which is located at the side of said second lens nearer to the image and which has a larger curvature than that at the side of said second lens nearer to the screen;

a third lens which consists of a meniscus lens having a concave surface located at the side of said third lens nearer to the image; and

a fourth lens having a concave surface which is located at the side of said fourth lens nearer to the screen and which has a larger curvature than that at the side of said fourth lens nearer to the image, said first to fourth lenses being arranged, respectively, from a side of the screen in the order named, the combined refracting power of said second and third lenses being larger than the refracting power of said first lens, at least one nonspherical surface being provided in said first lens, and at least one other nonspherical surface being provided in said second, third and fourth lenses.

2. A projection lens according to claim 1, wherein said at least one other nonspherical surface is provided in at least one of said second and third lenses.

3. A projection lens for enlarging an image onto a screen, comprising:

a first lens having a positive refracting power;

a second lens having a positive refracting power and a convex surface which is located at the side of said second lens nearer to said image and which has a larger curvature than that at the side of said second lens nearer to the screen;

a third lens which consists of a meniscus lens having a concave surface located at the side of said third lens nearer to the image; and

a fourth lens having a concave surface which is located at the side of said fourth lens nearer to the screen and which has a larger curvature than that at the side of said fourth lens nearer to the image, said first to fourth lenses being arranged, respectively, from a side of the screen in the order named, at least one nonspherical surface being provided in said first lens, at least one other nonspherical surface being provided in said second, third and fourth lenses, and said projection lens satisfying the following conditions;

space="preserve" listing-type="equation">0.75<

φ

2,3/φ

<

0.95 (1)

space="preserve" listing-type="equation">0.4F<

D.sub.2 <

0.6F (2)

space="preserve" listing-type="equation">0.45<

R.sub.5 /R.sub.6 <

0.85 (3)

where φ

is the refracting power of an entire system, φ

₂,3 is the combined refracting power of said second and third lenses, D₂ is the distance between opposing surfaces of said first and second lenses, R₅ is the radius of curvature of the surface of said third lens which is located on the side nearer to the screen, R₆ is the radius of curvature of the surface of said third lens which is located on the side nearer to the image, and F is the focal length of the entire lens system.

4. A projection lens for enlarging an image onto a screen, comprising:

a first lens having a positive refracting power;

a second lens having a positive refracting power and a convex surface which is located at the side of said second lens nearer to the image and which has a larger curvature than that at the side of said second lens nearer to the screen;

a third lens which consists of a meniscus lens having a concave surface located at the side of said third lens nearer to the image; and

a fourth lens having a concave surface which is located at the side of said fourth lens nearer to the screen and which has a larger curvature than that at the side of said fourth lens nearer to the image, said first to fourth lenses being arranged, respectively, from a side of the screen in the order named, at least one nonspherical surface being provided in said first lens, at least one nonspherical surface being provided in said second, third and fourth lenses, and said projection lens satisfying the following conditions;

5. 75<

φ

₂,3 /φ

<

0.90 (1)

space="preserve" listing-type="equation">0.4F<

D.sub.2 <

0.6F (2)

space="preserve" listing-type="equation">-300F<

R.sub.3 <

-5F (a negative sign indicates a concave shape toward the screen) (3)

space="preserve" listing-type="equation">0.45<

R.sub.5 /R.sub.6 <

0.85 (4)

where F is the focal length of the entire lens system, φ

is the refracting power of the entire lens system, φ

₂,3 is the combined refracting power of said second and third lenses, R₃ is the radius of curvature of the surface of said second lens which is located at the side nearer to the screen, R₅ is the radius of curvature of the surface of the third lens which is located at the side nearer to the screen, and R₆ is the radius of curvature of the surface of said third lens which is located at the side nearer to the image.

7. A projection lens according to claim 5, wherein the concave surface of said fourth lens is spherical.

6. A projection lens for projecting an image onto a screen, comprising:

a first lens having a positive refracting power;

a lens group having a second lens with a positive refracting power and a third lens having a refracting power of a smaller absolute value than that of the refracting power of the second lens; and

,

a fourth lens having a concave surface located at the side of said fourth lens nearer to the screen, said first lens, said lens group and said fourth lens being arranged, respectively, from a side of the screen in the order named, wherein the refracting power of said lens group is larger than that of said first lens, each of said first lens and said third lens comprises a plastic lens, and said second lens comprises a glass lens.