| abstract |
In an optical system (ZL) capable of imaging in a plurality of object side media (for instance, air and water) whose refractive indexes are different from each other, the optical system is composed of, in order from an object, a front lens group (G 1 ) whose position in an optical axis fixed, and a rear lens group (for instance, G 2 to G 4 ), and the rear lens group comprises at least two moving lens groups (for instance, G 2 and G 3 ), and at least two moving lens groups in the rear lens group are moved along the optical axis upon changing between object side media. |