Patent ID: 7154681

Claim:
A subminiature optical system having an aperture stop arranged closest to an object side, comprising, sequentially from the object side: a first lens group having a first lens of plus refractive power and a second lens of minus refractive power, the second lens being cemented to the first lens; a second lens group having a third lens where at least one refraction surface is aspherical and has minus refractive power; and a third lens group having a fourth lens where at least one refraction surface is aspherical and has minus refractive power, in which a refractive power of the first lens group satisfies the following Equation 1 and a dimension of an optical axis direction in the whole lens system satisfies the following Equation 2; 0.5 <f I /f <0.8 Equation 1 TL/f <1.45 Equation 2 where f I : composite focal length of the first lens group f: composite focal length of the whole lens system TL: distance from the aperture stop up to an image plane.