Imaging lens comprising a diffractive optical surface

• US 9,341,857 B2
• Filed: 05/20/2013
• Issued: 05/17/2016
• Est. Priority Date: 05/30/2012
• Status: Active Grant

• Current Assignee: Tokyo Visionary Optics Company Limited
• Original Assignee: Kantatsu Company Limited (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Suzuki, Hisanori, Sekine, Yukio
• Primary Examiner(s): Pham, Thomas K
• Assistant Examiner(s): Pasko, Nicholas R
• Application Number:
  US13/898,120
• Publication Number:
  US 20130321920A1
• Time in Patent Office: 1,093 Days
• Field of Search: 359/715, 359/780
• US Class Current: 1/1
• CPC Class Codes: G02B 13/004 having four lenses
• 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
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/0056 by using a diffractive optical element
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 9/34 having four components only

Abstract

An imaging lens includes, from the object side to the image side, an aperture stop, a first lens with positive refractive power having a convex object-side surface near an optical axis, a second lens with positive refractive power having a convex image-side surface near the axis, a third lens with positive refractive power having a convex image-side surface near the axis, and a fourth lens with negative refractive power having a concave image-side surface near the axis, wherein all lens surfaces are aspheric, all lenses are made of plastic material, a diffractive optical surface is formed on at least one of the lens surfaces from the first lens image-side surface to the second lens image-side surface, and at least one of the three positive lenses satisfies 1.58<Ndi where Ndi is the refractive index of the i-th positive lens at the d-ray.

Claims

1. An imaging lens for a solid-state image sensor in which lenses are arranged in order from an object side to an image side, comprising:

an aperture stop;

a first lens as a meniscus lens with positive refractive power having a convex surface on the object side near an optical axis;

a second lens as a meniscus lens with positive refractive power having a convex surface on the image side near the optical axis;

a third lens as a meniscus lens with positive refractive power having a convex surface on the image side near the optical axis; and

a fourth lens as a meniscus lens with negative refractive power having a concave surface on the image side near the optical axis,

wherein all lens surfaces are aspheric;

wherein all the lenses are made of plastic material;

wherein a diffractive optical surface is formed on at least one of lens surfaces from an image-side surface of the first lens to an image-side surface of the second lens;

wherein at least one of the three lenses with positive refractive power satisfies a conditional expression (1) below;

1.58<

Ndi 

 

(1)

where

Ndi;

refractive index of the at least one of the three positive lenses at d-ray;

wherein a conditional expression (2) below is satisfied;

0.7<

TTL/(2IH)<

0.9 

 

(2)

where

TTL;

distance on the optical axis from the object-side surface of the first lens to an image plane (a total track length), and

IH;

maximum image height;

wherein a conditional expression (3) below is satisfied;

0.7<

f1/f<

1.1 

 

(3)

where

f1;

focal length of the first lens, and

f;

focal length of an overall optical system and

wherein an F-value of the imaging lens falls in the range from 2.31 to 2.41.

2. The imaging lens according to claim 1, wherein a conditional expression (4) below is satisfied:

0.40<

r1/f<

1.0 

 

(4)

where

r1;

curvature radius of the object-side surface of the first lens, and

f;

focal length of the overall optical system.

3. The imaging lens according to claim 1, wherein a conditional expression (5) below is satisfied:

0.6<

f123/f<

0.9 

 

(5)

where

f123;

composite focal length of the first, second, and third lenses, and

f;

focal length of an overall optical system.

4. The imaging lens according to claim 1, wherein the object-side surface and image-side surface of the fourth lens have a pole-change point off the optical axis.

5. The imaging lens according to claim 1, wherein a conditional expression (6) below is satisfied:

0.6<

Σ

d/TTL<

0.8 

 

(6)

where

Σ

d;

distance on the optical axis from the object-side surface of the first lens to the image-side surface of the fourth lens, and

TTL;

distance on the optical axis from the object-side surface of the first lens to the image plane (a total track length).

6. The imaging lens according to claim 1, wherein a conditional expression (7) below is satisfied:

0.02<

T12/Σ

d<

0.20 

 

(7)

where

T12;

distance on the optical axis from the image-side surface of the first lens to the object-side surface of the second lens, and

Σ

d;

distance on the optical axis from the object-side surface of the first lens to the image-side surface of the fourth lens.

7. The imaging lens according to claim 1, wherein the first lens, the second lens, the third lens, and the fourth lens satisfy a conditional expression (8) below:

0.6<

Tie/Ti<

1.3 

 

(8)

where

Ti;

center thickness of an i-th lens, and

Tie;

edge thickness of the i-th lens.

8. The imaging lens according to claim 1, wherein a conditional expression (9) below is satisfied:

1≦

Dn≦

20

where

Dn;

a number of a diffraction grating of the diffractive optical surface (integer).