Imaging device
Provided is an imaging device for mobile devices such as a mobile phone, using a high resolution image sensor such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS).
1. An imaging device equipped with a photodetector, the imaging device comprising:
a first lens having a positive or negative refractive power;
a second lens having a positive or negative refractive power and including an object side which is concave;
a third lens having a positive or negative refractive power and including an object side and an imaging side which are both aspherical; and
a fourth lens having a positive or negative refractive power and including an object side and an imaging side which are both aspherical,
wherein the first lens to the fourth lens are arranged in sequence from an object, and
the imaging device meets Conditional Expression 1 to Conditional Expression 3:
0.25 <FBL/f< 0.35 [Conditional Expression 1]
3.5 <OL/FBL< 4.5 [Conditional Expression 2]
f/D≦ 2.6 [Conditional Expression 3]
where FBL denotes a distance from a last imaging side to a photodetector of a device part in the imaging device, OL denotes a distance from the object side of the first lens to the photodetector with reference to an optical axis, f denotes a focal length of the imaging device with reference to the optical axis, and D denotes an aperture of an entrance pupil of the imaging device.
2. The imaging device of claim 1 , further including an aperture diaphragm disposed at the object side of the first lens or between the first lens and the second lens.
3. The imaging device of claim 1 , wherein at least one of the first lens to the fourth lens has a refractive index of about 1.610 or greater with reference to the refractive index.
4. The imaging device of claim 1 , wherein the second lens meets Conditional Expression 4:
−5.0 >L 2 R 1>−10.0 [Conditional Expression 4]
where L2R1 denotes a radius of the object side of the second lens.
5. The imaging device of claim 1 , wherein the second lens meets Conditional Expression 5-1:
0.5 <L 2 R 2<4.0, and [Conditional Expression 5-1]
wherein the fourth lens meets Conditional Expression 5-2:
0.5 <L 4 R 2<4.0 [Conditional Expression 5-2]
where L2R2 denotes a radius of the imaging side of the second lens and L4R2 denotes a radius of the imaging side of the fourth lens.
6. The imaging device of claim 1 , wherein the second lens meets Conditional Expression 6:
1.5 <f 1<2.5 [Conditional Expression 6]
where f1 denotes a focal length of the first lens.
7. The imaging device of claim 1 , wherein the second lens meets Conditional Expression 7:
−4.0 <f 2<−3.0 [Conditional Expression 7]
wherein, f2 denotes a focal length of the second lens.