| 摘要 |
PURPOSE:To maintain stable and excellent imaging performance even if the optical path length of a transparent object disposed between an objective lens and an object surface changes while having a high magnification and large numerical aperture by constituting the 3rd lens group movably relatively with the 2nd lens group and the 4th lens group. CONSTITUTION:The 3rd lens group G3 is moved to the 4th lens group G4 side when the optical path length of a parallel flat plate as the transparent object disposed between the objective lens and the object surface, i.e., the value of the product of the thickness and refractive index is larger than a reference value. The 3rd lens group G3 is moved to the 2nd lens group G2 side when the optical path length of the parallel flat plate is smaller than the reference value. An aberration is thus corrected. The extent of the movement of the 3rd lens group G3 necessary for the aberration correction is decreased and the correction in a large range is made possible by providing high refracting power to the 3rd lens group G3.
|
