| 摘要 |
<p>An objective lens (OL) is provided with a first lens group (G1), a second lens group (G2), and a diffraction optical device (GD). The first lens group is disposed on the object side, has a positive refractive power as a whole, and is provided with a positive lens (planoconvex lens (L1)) disposed closest to the object side with a lens surface thereof closest to the object side being formed into a flat surface or a surface with a gentle curvature and at least one or more cemented lenses (cemented lens (CL12) and the like). The second lens group is disposed on the image side, has a negative refractive power as a whole, and is provided with a strong concave surface facing the image side and a strong concave surface facing the object side, which are opposite to each other. The diffraction optical device is provided with a diffraction optical surface (D) by which two diffraction device elements formed of different optical materials are joined and in the joint surface of which diffraction grating grooves are formed, and is disposed closer to the object side than a position at which a main beam and an optical axis cross.</p> |
