Image pickup lens, image pickup apparatus, and portable terminal device

1. An image pickup lens, comprising:

a first lens having a positive meniscus shape convex toward an object side;

a second lens disposed on an image side of the first lens and has a meniscus shape convex toward the image side; and

an aperture stop disposed on the object side of the image side surface of the first lens,

wherein the image pickup lens is configured to satisfy conditional expressions given below:

0.45 <R 2/ R 3<0.66  (5-2)

0.05 <DD/f< 0.117  (9-2)

where,

f is a focal length of the entire lens system;

R 2 is a paraxial radius of curvature of the object side surface of the first lens;

R 3 is a paraxial radius of curvature of the image side surface of the first lens; and

DD is a distance, on the optical axis, between the first and second lenses.

2. The image pickup lens of claim 1 , further satisfying a conditional expression given below:

0.45 <R 5 /R 6<1.55  (11)

where,

R 5 is a paraxial radius of curvature of the object side surface of the second lens; and

R 6 is a paraxial radius of curvature of the image side surface of the second lens.

3. The image pickup lens of claim 1 , wherein the aperture stop is disposed between a surface apex position and an edge position of the object side surface of the first lens.

4. The image pickup lens of claim 1 , further comprising a field stop between the first and second lenses.

5. The image pickup lens of claim 1 , further satisfying a conditional expression given below:

0<( D 5− D 2)/ f< 0.23  (12)

where,

D 2 is a thickness of the first lens on the optical axis; and

D 5 is a thickness of the second lens on the optical axis.

6. The image pickup lens of claim 1 , wherein the image side surface of the first lens is a concave surface and the image pickup lens further satisfies a conditional expression given below:

0.2 <R 3 /f< 0.52  (13).

7. The image pickup lens of claim 1 , wherein the second lens has a positive refractive power and the image pickup lens further satisfies a conditional expression given below:

0 <f 2 /f< 100  (10-2)

where, f2 is a focal length of the second lens.

8. The image pickup lens of claim 1 , further satisfying a conditional expression given below:

| Nd 1− Nd 2|≦0.01  (14)

where,

Nd 1 is a refractive index of the first lens with respect to d-line; and

Nd 2 is a refractive index of the second lens with respect to d-line.

9. The image pickup lens of claim 1 ,

further satisfying a conditional expression given below:

|ν d 1−ν d 2|<0.1  (15)

where,

νd 1 is an Abbe number of the first lens with respect to d-line; and

νd 2 is an Abbe number of the second lens with respect to d-line.

10. A portable terminal device, comprising:

an image pickup apparatus having the image pickup lens of claim 1 and an image sensor for outputting an imaging signal according to an optical image formed by the image pickup lens; and

a display unit for displaying an image taken by the image pickup apparatus.