Optical system and image pickup apparatus including the same

Patent metadata

Field	Value
Publication number	US-9618731-B2
Application number	US-201615091850-A
Country	US
Kind code	B2
Filing date	Apr 6, 2016
Priority date	Apr 13, 2015
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

Provided is an optical system, including, in order from an object side to an image side: a front group having a negative refractive power; an aperture stop; and a rear group having a positive refractive power, in which: the front group consists of in order from the object side to the image side: a negative first lens (L 1 ) having a concave surface facing the image side; a second lens (L 2 ); and a third lens (L 3 ); the rear group consists of, in order from the object side to the image side: a positive fourth lens (L 4 ); and a negative cemented lens (L 56 ), which is obtained by cementing a positive fifth lens (L 5 ) and a negative sixth lens (L 6 ); and a focal length f 56 of the cemented lens (L 56 ) and a focal length f of the optical system are each appropriately set.

First claim

What is claimed is:

1. An optical system, comprising, in order from an object side to an image side:
a front group having a negative refractive power;
an aperture stop; and
a rear group having a positive refractive power, wherein:
the front group consists of, in order from the object side to the image side:
a first lens having a negative refractive power and having a concave surface facing the image side;
a second lens; and
a third lens;

the rear group consists of, in order from the object side to the image side:
a fourth lens having a positive refractive power; and
a cemented lens having a negative refractive power, which is obtained by cementing a fifth lens having a positive refractive power and a sixth lens having a negative refractive power; and

the following conditional expression is satisfied:
−130.0< f 56/ f<− 10.0

where f56 represents a focal length of the cemented lens, and f represents a focal length of the optical system.

2. An optical system according to claim 1 , wherein the following conditional expression is satisfied:
−1.0< f 6/ f 5<−0.7

where f5 represents a focal length of the fifth lens, and f6 represents a focal length of the sixth lens.

3. An optical system according to claim 1 , wherein the following conditional expression is satisfied:
1.2< f 4/ f< 2.0

where f4 represents a focal length of the fourth lens.

4. An optical system according to claim 1 , wherein the following conditional expression is satisfied:
4.5< D/f< 8.0

where D represents an entire lens length.

5. An optical system according to claim. I, wherein the following conditional expression is satisfied:
1.85<Nd6<2.40

where Nd6 represents a refractive index of a material of the sixth lens.

6. An optical system according to claim 1 , wherein the following conditional expression is satisfied:
Sk/f< 2.0

where Sk represents an air-equivalent distance from a lens surface of the sixth lens on the image side to an image plane.

7. An optical system according to claim 1 , wherein:
the front group comprises:
a lens (Lp) having a positive refractive power; and
a lens (Ln) having a negative refractive power, which is arranged adjacently on the object side of the lens (Lp); and

the following conditional expression is satisfied:
−10.0<( Rn+Rp )/( Rn−Rp )<−0.8

where Rn represents a curvature radius of a lens surface of the lens (Ln) on the image side, and Rp represents a curvature radius of a lens surface of the lens (Lp) on the object side.

8. An optical system according to claim. 7 , wherein:
the second lens comprises a negative lens having a concave surface facing the image side;
the third lens comprises a positive lens having a convex surface facing the object side;
the second lens corresponds to the lens (Ln); and
the third lens corresponds to the lens (Lp).

9. An optical system according to claim 7 , wherein:
the second lens comprises a positive lens having a convex surface facing the object side;
the third lens comprises a negative lens having a concave surface facing the image side;
the first lens corresponds to the lens (Ln); and
the second lens corresponds to the lens (Lp).

10. An image pickup apparatus, comprising:
an optical system; and
a photo-electric conversion element configured to receive light of an image formed by the optical system,
the optical system comprising, in order from an object side to an image side:
a front group having a negative refractive power;
an aperture stop; and
a rear group having a positive refractive power, wherein:
the front group consists of, in order from the object side to the image side:
a first lens having a negative refractive power and having a concave surface facing the image side;
a second lens; and
a third lens;

the rear group consists of, in order from the object side to the image side:
a fourth lens having a positive refractive power; and
a cemented lens having a negative refractive power, which is obtained by cementing a fifth lens having a positive refractive power and a sixth lens having a negative refractive power; and

the following conditional expression is satisfied:
−130.0< f 56/ f<− 10.0

where f56 represents a focal length of the cemented lens, and f represents a focal length of the optical system.

Assignees

• Canon Kk

Inventors

• Ikegaya Yuki

Classifications

• G02B13/04 Primary

  Reversed telephoto objectives · CPC title

• G02B9/10

  one + and one - component · CPC title

• G02B13/006

  at least one element being a compound optical element, e.g. cemented elements · CPC title

• G02B9/60

  having five components only · CPC title