Auto-focusing optical system for camera module
The present invention relates to an auto-focusing optical system, and more particularly, to an auto-focusing optical system for a camera module, capable of obtaining a high resolution in a small size using a liquid lens whose curvature is varied depending on an applied voltage. In the auto-focusing optical system, a first lens group has a liquid lens whose curvature is varied and having a plus optical power, a second lens group has a plus optical power, and a third lens group has a minus optical power. Thanks to an auto-focusing optical system including a liquid lens according to the present invention, not only a manufacturing in a small size is possibly realized but also a high resolution can be obtained, and power consumption is small.
1. An auto-focusing optical system comprising, sequentially from an object side:
a first lens group having a plus optical power, the first lens group including a liquid lens in which a curvature of a boundary surface formed between different liquids included in an inside is varied depending on an applied voltage so that the boundary surface performs a function of a lens' surface, and an aspherical lens having an aspherical surface formed on at least one refractive surface thereof;
a second lens group having a plus optical power, and including an aspherical lens having an aspherical surface formed on at least one refractive surface thereof;
a third lens group a minus optical power, and including an aspherical lens having an aspherical surface formed on at least one refractive surface thereof; and
wherein the curvature of the boundary surface of the liquid lens is varied so that an auto-focusing is performed.
2. The system of claim 1 , wherein a refraction power of the liquid lens satisfies the following Equation 1:
−7< D< 35 Equation 1,
wherein D is refraction power of a surface of the liquid lens whose curvature is varied (unit: diopter).
3. The system of claim 2 , wherein an optical axial direction measure of the whole lens group satisfies the following Equation 2:
oal/f< 2.0 Equation 2,
wherein oal is distance between an aperture stop up to an image plane, and
f is composite focal length of the whole lens.
4. The system of claim 2 , wherein a power of the first lens group satisfies the following Equation 3:
0.85< f 1/ f< 1.5 Equation 3,
wherein f 1 is composite focal length of the first lens group.
5. The system of claim 4 , wherein a power of the third lens group satisfies the following Equation 4:
2.0< |f 3/ f|< 5.5 Equation 4,
wherein f 3 is composite focal length of the third lens group.
6. The system of claim 1 , wherein the first lens group comprises, sequentially from an object side:
a first lens that corresponds to a cover surface of the liquid lens;
a second lens including the liquid lens; and
a third lens that corresponds to an upper cover surface of the liquid lens.
7. The system of claim 6 , further comprising an aperture stop arranged most closely to the object side.
8. The system of claim 1 , further comprising an aperture stop arranged most closely to the object side.