Patent ID: 7486450

Claim:
A lens system comprising, sequentially in that order from a magnifying side, a first lens group which makes up a substantially afocal optical system as a whole and a second lens group having a positive refractive power as a whole, the first lens group being configured to comprise, sequentially in that order from a magnifying side, a first sub-lens group or 1 a lens group having a negative refractive power as a whole and a second sub-lens group or 1 b lens group having a positive refractive power as a whole, the second lens group being configured to comprise, sequentially in that order from a magnifying side, a first sub-lens group or 2 a lens group having a negative refractive power as a whole and a second sub-lens group or 2 b lens group having a positive refractive power as a whole, wherein, the following conditional expression (1) is satisfied with respect to a power set for the first lens group, the following conditional expression (2) is satisfied with respect to an afocal magnification set for the first lens group, the following conditional expression (3) is satisfied with respect to a power set for the 1 a lens group, the following conditional expression (4) is satisfied with respect to a power set for the 2 a lens group, the following conditional expression (5) is satisfied with respect to a power set for the 2 b lens group, and the following conditional expression (6) is satisfied with respect to a thickness dimension at an optical axis of the first lens group; −0.5 ≦f/f I ≦−0.1 (1) 0.3 ≦h IE /h IX ≦0.5 (2) −1.5 ≦f/f Ia ≦−0.5 (3) −0.3 ≦f/f IIa ≦0.3 (4) 0.15 ≦f/f IIb ≦0.7 (5) 1.6 ≦T I /f≦ 2.6 (6) where, f: Composite focal length of the whole lens system; f I : Composite focal length of the first lens group; h IE : Height of paraxial ray incident on to a magnifying-side surface of a lens element which is disposed outermost on a magnifying side of the first lens group; h IX : Height of paraxial ray emerging from a contracting-side surface of a lens element which is disposed outermost on a contracting side of the first lens group; f Ia : Composite focal length of the 1 a lens group which makes up the first lens group; f IIa : Composite focal length of the 2 a lens group which makes up the second lens group; f IIb : Composite focal length of the 2 b lens group which makes up the second lens group; and T I : Distance on the optical axis between the magnifying-side surface of the lens element which is disposed outermost on the magnifying side of the first lens group to the contracting-side surface of the lens element which is disposed outermost on the contracting side of the first lens group.