Retro-focus type wide angle lens

• US 4,310,222 A
• Filed: 04/18/1979
• Issued: 01/12/1982
• Est. Priority Date: 10/29/1976
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Ikemori, Keiji
• Primary Examiner(s): Clark, Conrad J.
• Application Number:
  US06/031,613
• Time in Patent Office: 1,000 Days
• Field of Search: 350/432, 350/458
• US Class Current: 359/708
• CPC Class Codes: G02B 13/04 Reversed telephoto objectives
• 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

The present invention relates to a retro-focus type wide angle lens which is compact despite its remarkably large field of view and well compensated for various aberrations.

This lens system consists of the first divergent lens group and the second convergent lens group in sequence from the side of the object, whereby the first divergent group consists of a plural number of meniscus lenses convex to the object in such a manner that the distortion is compensated for and a compact lens system is realized by forming the object side surface of the substantially zero first order power lens in the meniscus lenses non spherical. The meniscus lens with non-spherical surface is formed from plastic material, resulting in an inexpensive and light retro-focus type wide angle lens.

Further, the second convergent lens group is divided into two lens groups with a diaphragm as boundary, whereby in the object side lens group a meniscus lens concave to the object and a biconvex lens are arranged in sequence from the diaphragm to the object side so as to form an air lens having a divergent effect between both lenses, while in the image plane side lens group a lens concave to the image is arranged so as to eliminate the astigmatism and the spherical aberration.

Claims

1. A retro-focus type wide angle lens for forming an image of an object at an image plane comprising:

a divergent lens group including;

two sets of sub-lens groups each consisting of at least one first meniscus lens having a negative refractive power and a surface convex on the object side; and

a lens group arranged between said two sets of sub-lens groups and comprising meniscus lens convex on the object side, the surface of the lens group closest to the object being non-spherical for distortion compensation; and

a convergent lens group on the image side against said divergent lens group including;

a front lens group including a diaphragm, a second negative meniscus lens concave on the object side, and a biconvex lens in sequence from the diaphragm to the object so as to form a divergent air lens between said second negative meniscus lens and said biconvex lens; and

a rear lens group having a plural number of lens surfaces and provided on the image side with reference to the diaphragm, at least one of said lens surfaces being concave on the image side.

2. A retro-focus type wide angle lens in accordance with claim 1, wherein said non-spherical surface is so formed that the more distant it is from the optical axis of the lens system, the greater the deviation from an ideal spherical surface, the radius of the paraxial curvature being larger than the radius of curvature of the surface next to the non-spherical surface at the object side.

3. A retro-focus type wide angle lens in accordance with claim 2, wherein the absolute value paraxial focal length of the lens having said non-spherical surface is larger than twenty-five times the effective total focal length of the wide angle lens.

4. A retro-focus type wide angle lens in accordance with claim 1, wherein the distance between the diaphragm and the image side of the biconvex lens in said front lens group is larger than 0.15 times the effective focal length of the wide angle lens but smaller than 0.85 times said effective focal length.

5. A retro-focus type wide angle lens in accordance with claim 4, wherein the front lens group consists, in sequence from the diaphragm to the object side of said negative meniscus lens said biconvex lens, and a further biconvex lens which consists of a negative lens and a positive lens cemented to each other.

6. A retro-focus type wide angle lens in accordance with claim 1, wherein said rear lens group consists, in sequence from the diaphragm to the image side, of a meniscus lens consisting of two lenses cemented to each other, whereby the object side lens of said cemented meniscus lens is biconvex and the image side lens of said cemented meniscus lens is biconcave, and a further meniscus lens consisting of two further lenses cemented to each other, whereby the object side further lens is biconcave and the image side further lens is biconvex, and a biconvex lens.

7. A retro-focus type wide angle lens in accordance with claim 1, wherein said rear lens group consists, in sequence from the diaphragm to the image side, of a meniscus lens consisting of two meniscus lenses cemented to each other both being convex on the object side, a further meniscus lens consisting of two further lenses, whereby the further lens on the object side is biconvex and the further lens on the image side is biconvex, and a biconvex lens.

8. A retro-focus type wide angle lens in accordance with claim 1, wherein said rear lens group consists, in sequence from the diaphragm to the image side, of a negative meniscus lens being convex on the object side, a further negative meniscus lens consisting of two further lenses cemented to each other, whereby the further lens on the object side is biconcave and the lens on the image side is biconvex, and a biconvex lens.

15. A retro-focus type wide angle lens in accordance with claim 1 or 9, wherein the meniscus lens having said non-spherical surface is formed from plastic material.

16. A retro-focus type wide angle lens in accordance with claim 15, wherein said non-spherical surface is so formed that the more distant it is from the optical axis of the lens system, the greater the deviation from the spherical, the radius of the paraxial curvature being larger than the radius of curvature of the surface next to the non-spherical surface on the object side.

17. A retro-focus type wide angle lens in accordance with claim 16, wherein the absolute value paraxial focal length of the lens having said non-spherical surface is larger than 50 times the effective total focal length of the wide angle lens.

18. A retro-focus type wide angle lens in accordance with claim 15, wherein the distance between the diaphragm and the image side surface of the biconvex lens in said front lens group is larger than 0.15 times the effective focal length of the wide angle lens but smaller than 0.35 times said effective focal length.

19. A retro-focus type wide angle lens in accordance with claim 15, wherein said rear lens group consists, in sequence from said diaphragm to the image side, of a meniscus lens consisting of two lenses cemented to each other, whereby the object side lens of said cemented meniscus lens is biconvex and the image side lens of said cemented meniscus lens is biconcave and a further meniscus lens consisting of two further lenses cemented to each other, whereby the object side further lens is biconcave and the image side further lens is biconvex, and a biconvex lens.

9. A retro-focus type wide angle lens comprising:

a diaphragm; and

a front lens group on the object side of the diaphragm comprising;

a negative meniscus lens convex on the object side;

a meniscus lens of substantially zero first order power, having a convex non-spherical surface on the object side;

a negative meniscus lens group having at least one meniscus lens convex on the subject side;

a convergent lens group next to said negative meniscus lens group, including a lens pair which consists of a biconvex lens on the object side, and a negative meniscus lens concave on the object side and located on the image side in sequence form the object side immediately up to the diaphragm; and

a rear lens group on the image side of the diaphragm comprising;

a first meniscus lens concave on the image side;

a second positive meniscus lens convex on the image side and having a divergent cemented surface concave on the image side; and

a biconvex lens, in sequence from the object side.

10. A retro-focus type wide angle lens in accordance with claim 9, wherein said non-spherical surface has a deviation from a hypothetical spherical surface, which deviation increases toward the circumferential portions of the lens from the optical axis, while the radius of the paraxial curvature of the non-spherical surface is larger than the radius of curvature of the surface next to the non-spherical surface on the object side.

11. A retro-focus type wide angle lens in accordance with claim 9, wherein the distance between the diaphragm and the image side surface of said biconvex lens included in said convergent lens group in said front lens group is larger than 0.15 times the effective focal length of the wide angle lens but smaller than 0.85 times said effective focal length.

12. A retro-focus type wide angle lens in accordance with claim 9, wherein said convergent lens group in said front lens group consists of said lens pair, and further a biconvex lens consisting of a positive lens and a negative lens cemented to each other.

13. A retro-focus type wide angle lens in accordance with claim 9, wherein said first meniscus lens in said rear lens groups is a lens consisting of a biconvex lens on the object side and a biconcave lens on the image side cemented to each other.

14. A retro-focus type wide angle lens in accordance with claim 9, wherein said first meniscus lens in said rear lens group is a meniscus lens consisting of two meniscus lenses both having a convex surface on the object side, said two meniscus lenses being cemented to each other.