Optical system having a variable out-of-focus state

Abstract

An optical system includes a forward group having a first lens group of positive focal length and a seconds lens group of negative focal length, the forward group having a positive focal length, a stop, and a rearward group having a positive focal length. The forward group, the stop and the rearward group are disposed in the named order from the object side. The spacing between the first lens group and the second lens group may be varied along the optic axis to thereby fluctuate the spherical aberration and coma of the optical system and vary the depictive property of the image of the defocus area and also, fluctuate the astigmatism of the optical system following the fluctuations of the spherical aberration and coma, thereby maintaining the flatness of the image plane. The optical system is constructed so as to satisfy the following conditions: 0.5<.vertline.f.sub.2 /f.vertline.<1.0 0.5<.vertline.f.sub.1 /f.sub.2 .vertline.<1.5 where f is the focal length of the entire system of the optical system, and f.sub.1 and f.sub.2 are the focal lengths of the first lens group and the second lens group, respectively.

Dependencies are inferred from the claim text.