Optical lens assembly and method of forming image using the same

1. An optical lens assembly comprising:

a first lens having a convex object-side surface;

a second lens having a convex object-side surface;

at least one lens at an image side of the second lens;

a first stop being a variable stop at an object side of the first lens; and

a second stop between an image side of the first stop and the at least one lens at the image side of the second lens,

wherein the second stop determines a minimum F number, and the first stop is variable to determine an F number greater than the minimum F number,

wherein the optical lens assembly satisfies the following conditions:



d

⁢

⁢

2





sag

⁢

⁢

1



≤

0.9

⁢

⁢

0.2

≤

R

⁢

⁢

1

f

≤

0.8

〈

Conditions

〉

where sag1 denotes a sag value of the object-side surface of the first lens measured based on an effective diameter at the minimum F number, d2 denotes a distance measured from a vertex of the object-side surface of the first lens to the first stop along an optical axis, R1 denotes a radius of curvature of the object-side surface of the first lens, and f denotes a total focal length of the optical lens assembly.

2. The optical lens assembly of claim 1 , wherein the optical lens assembly satisfies the following condition:

0.4

<

Fno

⁢

⁢

1

Fno

⁢

⁢

2

<

0.8

〈

Condition

〉

where Fno1 denotes the minimum F number of the second stop, and Fno2 denotes an F number when the first stop is in a variably opened state.

3. The optical lens assembly of claim 1 , further comprising an image sensor, wherein the optical lens assembly satisfies the following condition:

1.0

<

TT

Y

1

⁢

⁢

H

<

1.8

〈

Condition

〉

where TT denotes a distance from the first stop to the image sensor along the optical axis, and Y IH denotes half a diagonal length of the image sensor.

4. The optical lens assembly of claim 1 , further comprising an image sensor, wherein the optical lens assembly satisfies the following condition:

0

<

t

⁢

⁢

21

Y

IH

<

1.0

〈

Condition

〉

where t21 denotes a distance from the first stop to the second stop along the optical axis, and Y IH denotes half a diagonal length of the image sensor.

5. The optical lens assembly of claim 1 , further comprising an image sensor, wherein the optical lens assembly satisfies the following condition:

0.1

<

s

⁢

⁢

2

Y

IH

<

0.5

〈

Condition

〉

where s2 denotes a radius of the first stop at its maximum F number, and Y IH denotes half a diagonal length of the image sensor.

6. The optical lens assembly of claim 1 , wherein the optical lens assembly satisfies the following condition:

0.4

<

f

f

⁢

⁢

2

<

1.6

〈

Condition

〉

where f2 denotes a focal length of the second lens.

7. The optical lens assembly of claim 1 , wherein the at least one lens at the image side of the second lens includes a third lens at the image side of the second lens, the third lens having negative refractive power and a concave image-side surface.

8. The optical lens assembly of claim 1 , wherein the optical lens assembly comprises at least three aspheric plastic lenses.

9. The optical lens assembly of claim 1 , wherein the optical lens assembly comprises at least one aspheric lens having at least one inflection point.

10. The optical lens assembly of claim 1 , wherein the first lens has positive refractive power.

11. The optical lens assembly of claim 1 , wherein the first lens has a meniscus shape.

12. The optical lens assembly of claim 1 , wherein, when the optical lens assembly is focused, the first stop and the second stop are moved together with the first lens, the second lens, and the at least one lens at the image side of the second lens.

13. The optical lens assembly of claim 1 , wherein the second stop is provided between the first lens and the second lens or provided at the image side of the second lens.