Patent ID: 6864961

Claim:
A projection optical system for forming a reduced image of a pattern on a first surface, onto a second surface, comprising, in order from the first surface side: a first lens unit having a negative refracting power; a second lens unit having a positive refracting power; a third lens unit having a negative refracting power; a fourth lens unit having a positive refracting power; an aperture stop; and a fifth lens unit having a positive refracting power; wherein the following conditions are satisfied: −1.3<1/β1<0, and 0.08< L 1 /L< 0.17, where β1 is a composite, lateral magnification of said first lens unit and said second lens unit, L1 is a distance from said first surface to a lens surface closest to said second surface in said second lens unit, and L is a distance from said first surface to said second surface.