Patent ID: 6507442
Filing Date: 2003-01-14
Classification: G02B

Abstract:
An objective lens comprising:a first lens unit constructed with a plurality of single lenses, having a negative power as a whole; and a second lens unit constructed with a plurality of single lenses, arranged on an object side of said first lens unit, wherein each of said first lens unit and said second lens unit is provided with air spaces between positive and negative lenses of different media and has at least one pair of lenses designed to satisfy the following conditions, and in addition to said pair of lenses, said second lens unit has at least one single positive biconvex lens and at least one single positive meniscus lens: 0.01<d d/L<0.01 0.88<Rp/Rn<1.14 where L is a parfocal distance of said objective lens in millimeters, d is an air apace in millimeters, Rp is a radius of curvature of a lens surface with a positive power opposite to the air space, and Rn is a radius of curvature of a lens surface with a negative power opposite to the air space, andwherein said second lens unit has at least three pairs of lenses and satisfies the following condition: &ngr; dp>&ngr; dnwhere &ngr; dp is an Abbe's number of each of positive lenses contained in said pairs of lenses and v dn is an Abbe's number of each of negative lenses contained in said pairs of lenses.