Patent ID: 8300325

Claim:
An objective lens comprising a first negative lens, a second positive lens, an aperture stop, a third positive lens, and a joined lens arranged in order from an object side, the joined lens being formed of a fourth positive lens and a fifth negative lens that are joined together, wherein the joined lens satisfies conditional expressions (1) and (2), and the objective lens satisfies conditional expression (3): nn≧ 2.0 (1) 12<(ν p−νn )<34 (2) 1.52<( f 23/fl)<1.75 (3) where nn denotes a refractive index with respect to a d-line of the fifth lens, νp denotes an Abbe number of the fourth lens, νn denotes an Abbe number of the fifth lens, f 23 denotes a combined focal length of the second lens and the third lens, and fl denotes a focal length of the entire system.