1.  Field of the Invention
The present invention relates to a microscope objective lens, and, more particularly, to a microscope objective lens with a modulation contrast apparatus housing a modulator. 
2.  Description of the Related Art
Conventionally, microscope objective lenses used as modulation contrast devices have a modulator located within the objective lens, fixed at the pupil position of the objective lens, and cannot be rotated.  A modulator is an optical member, as shown for example in FIG.  3.  A first partial area 41 at one edge of the circular pupil area 40 of the objective lens has a permeability rate of 1%.  A second partial area 42 extending from the first partial area 41 on the optical axis side of the objective lens has a permeability rate of 10%.  The remaining area 43 has a permeability rate of 100%.  The subject sample contrast is improved by using this member in the pupil position of objective lens. 
Objective lenses using modulation contrast devices have the kinds of problems discussed below. 
(1) Since the directions of shadowing for dark-light contrast on a three-dimensional object are unilateral, observations are made from a direction that is inappropriate depending on the direction of the sample or the item observed, so the performance of the objective lens is hindered. 
(2) A sample area is first located under lower magnification, and the lens turret is then shifted so that a higher magnification objective lens may be utilized for a closer examination of the sample area.  However, the orientations of the modulators of the two lenses differ, making observations difficult.