IMAGING LENS COMPOSED OF SIX OPTICAL ELEMENTS

• US 20150241665A1
• Filed: 02/23/2015
• Published: 08/27/2015
• Est. Priority Date: 02/24/2014
• Status: Active Grant

• Current Assignee: Tokyo Visionary Optics Company Limited
• Original Assignee: Kantatsu Company Limited (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Hashimoto, Masaya
• Granted Patent: US 9,535,235 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 13/0045 having five or more lenses
• CPC Class Codes: G02B 13/0055 employing a special optical element
• 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 9/62 having six components only

Abstract

A compact low-profile low-cost imaging lens with an F-value of 2.5 or less and a wide field of view which corrects aberrations properly. Its elements are arranged from an object side: a first positive optical element group including a first positive lens having a convex object-side surface and a second negative lens having a concave image-side surface; a second positive optical element group including a third positive lens having a convex image-side surface; and a third negative optical element group including a fourth negative double-sided aspheric lens having a concave image-side surface and a fifth double-sided aspheric lens having a concave object-side surface. The fourth lens image-side surface has at least one pole-change point off an optical axis. A double-sided aspheric aberration correction optical element with virtually no refractive power is located in an air gap between the first and second optical element groups.

Claims

1. An imaging lens composed of six optical elements which forms an image of an object on a solid-state image sensor, in which the elements are arranged in order from an object side to an image side, comprising:

a first optical element group with positive refractive power including

a first lens with positive refractive power having a convex surface on the object side as a first optical element; and

a second lens with negative refractive power having a concave surface on the image side as a second optical element;

a second optical element group with positive refractive power including a third lens with positive refractive power having a convex surface on the image side as a third optical element; and

a third optical element group with negative refractive power including

a fourth double-sided aspheric lens with negative refractive power having a concave surface on the image side as a fourth optical element; and

a fifth double-sided aspheric lens having a concave surface on the object side as a fifth optical element, wherein

the image-side surface of the fourth lens has at least one pole-change point off an optical axis; and

as a sixth optical element, a double-sided aspheric aberration correction optical element with virtually no refractive power is located in an air gap between the first optical element group and the second optical element group.

2. The imaging lens composed of six optical elements according to claim 1,

wherein conditional expressions (1) and (2) below are satisfied:

0.1<

TN/f<

0.5 

 

(1)

40<

ν

dN<

60 

 

(2)

where

TN;

distance on the optical axis between lenses where the aberration correction optical element is located

f;

focal length of an overall optical system of the imaging lens

ν

dN;

Abbe number of the aberration correction optical element at d-ray.

3. The imaging lens composed of six optical elements according to claim 1,

wherein aspheric surfaces on both sides of the aberration correction optical element are shaped so as to curve toward the object side with increasing distance from the optical axis.

4. The imaging lens composed of six optical elements according to claim 1,

wherein a conditional expression (3) below is satisfied:

1.0<

fLG1/f<

2.0 

 

(3)

where

fLG1;

focal length of the first optical element group.

5. The imaging lens composed of six optical elements according to claim 1,

wherein a conditional expression (4) below is satisfied:

0.3<

fLG2/f<

1.0 

 

(4)

where

fLG2;

focal length of the second optical element group.

6. The imaging lens composed of six optical elements according to claim 1,

wherein a conditional expression (5) below is satisfied:

−

0.8<

fLG3/f<

−

0.2 

 

(5)

where

fLG3;

focal length of the third optical element group.

7. The imaging lens composed of six optical elements according to claim 1,

wherein a conditional expression (6) below is satisfied:

0.8<

(r5+r6)/(r5−

r6)<

2.5 

 

(6)

where

r5;

curvature radius of the object-side surface of the third lens

r6;

curvature radius of the image-side surface of the third lens.