Stereomicroscope

A stereomicroscope comprising, in order from an object side:

• a single objective lens system;
• afocal relay optical systems, each including a front lens unit with positive refracting power and a rear lens unit with positive refracting power and having an intermediate image between the front lens unit and the rear lens unit;
• variable magnification optical systems;
• a plurality of aperture stops including at least aperture stops for right and left eyes, located at positions decentered from an optical axis of the objective lens system;
• and
• a plurality of imaging lens systems located at positions corresponding to the plurality of aperture stops,
• wherein an illumination optical system is located in the proximity of an entrance pupil of an optical system ranging from the objective lens system to each of the imaging lens systems and when each of the variable magnification optical systems lies at a low-magnification position, the entrance pupil of the optical system ranging from the objective lens system to each of the imaging lens systems is located closest to the objective lens system to satisfy the following conditions:
• 0<L—enp_w/f—ob<0.3
• 0.5<f—rf/f—rr<0.9
• 0.1<f—rf/f—ob<0.4
• −0.1<Δz/f—ob<0.3
• where L_enp_w is a distance from a most object-side surface of the objective lens system where a working distance is shortest to the entrance pupil at a low-magnification position, in which a symbol where the entrance pupil is located on an image side of the most object-side surface of the objective lens system is taken as a positive;
• f_ob is a focal length of the objective lens system where the working distance is shortest;
• f_rf is a focal length of the front lens unit of each of the afocal relay optical systems;
• f_rr is a focal length of the rear lens unit of each of the afocal relay optical systems;
• and Δz is a distance from the most object-side surface of the illumination optical system where the working distance is shortest to the entrance pupil at the low-magnification position, in which a symbol where the entrance pupil is located on the image side of the most object-side surface of the illumination optical system is taken as a positive.