Patent ID: 6452728
Filing Date: 2002-09-17
Classification: G02B

Abstract:
A retrofocus lens system comprising in order from a large conjugate side toward a small conjugate side:a first lens group having a negative refracting power; a second lens group having a positive refracting power; and a third lens group having a positive refracting power; said first lens group including in order from the large conjugate side toward the small conjugate side, a first lens having an aspheric surface, a meniscus second lens having a negative refracting power and having a convex surface on the large conjugate side, a meniscus third lens having a negative refracting power and having a convex surface on the large conjugate side, and a meniscus fourth lens having a negative refracting power and having a convex surface on the small conjugate side; said second lens group including in order from the large conjugate side toward the small conjugate side, a fifth lens having a positive refracting power, and a sixth lens joined to said fifth lens; said third lens group including in order from the large conjugate side toward the small conjugate side, a meniscus seventh lens having a positive refracting power and having a convex surface on the small conjugate side, a biconcave eighth lens, a ninth lens joined to said eighth lens and having a positive refracting power, a biconvex tenth lens, a biconvex eleventh lens, and a twelfth lens having an aspheric surface; wherein said retrofocus lens system satisfies the following expressions: 0.82/f3<1.5 1.61|/f<2.4 |f4|/f>30 f5/f>6 where f is a focal distance of the whole lens system, f2 is a focal distance of said second lens group, f3 is a focal distance of said third lens group, |f1| is an absolute value of a focal distance of said first lens group, |f4| is an absolute value of an axial focal distance of said first lens, and f5 is an axial focal distance of said twelfth lens.