For a positive lens having a convex surface on an image side thereof and a diaphragm
provided on an object side thereof, the following conditions are satisfied when
a surface of the lens at least on the image side is aspheric, a focal length is
f, a distance from the diaphragm to a front surface of the lens is D0, and
a thickness of the lens is D1: 0.2D0/f0.8, 1.2(D0+D1)/f,
and 0.4R2/f1.0.
