Patent ID: 7443599

Claim:
A magnification varying optical system that directs light from an object to an image sensor, comprising from the object side to an image side: a first lens unit having negative optical power, and including an optical axis changing element that changes an optical axis; a second lens unit having positive optical power, and including three lens elements, the second lens unit having: a positive lens element having a convex surface on the object side, in a most object side position; a negative lens element; and a positive lens element; a third lens unit having negative optical power; and a fourth lens unit having positive optical power, wherein in magnification varying from a wide-angle end to a telephoto end, the first lens unit is stationary, a distance from the first lens unit to the second lens unit decreases, a distance from the third lens unit to the fourth lens unit increases, and the magnification varying optical system satisfies the following conditions: −2.0 <f — GR 1 — o/fm<− 0.5, and −1.2<[ r — GR 2 — o+r — GR 2 — i]/[r — GR 2 — o−r — GR 2 — i]< 0 where f_GR 1 _o is a focal length of a lens element situated on the object side of the optical axis changing element in the first lens unit; fm is (fw×ft) 1/2 ; fw is an overall focal length of the magnification varying optical system at the wide-angle end; ft is an overall focal length of the magnification varying optical system at the telephoto end; r_GR 2 _o is a radius of curvature of an object side surface of the most object side positive lens element in the second lens unit; and r_GR 2 _i is a radius of curvature of an image side surface of the most object side positive lens element in the second lens unit, wherein the magnification varying optical system further satisfies the following conditions: −1.3< f 1 /fm<− 0.5, and 0.5< f 2 /fm< 1.5, where f 1 is a focal length of the first lens unit, and f 2 is a focal length of the second lens unit.