Condenser centering is maintained by a locating pin (A). The condenser focus knob (B) is used to engage or disengage from the pin. Knob C swings out the top lens.
The condenser top lens is moved out of the optical path for low magnification imaging.
The polarizer for this microscope is a Nicol prism embedded in the condenser (shown in green). The mirror shows its central position (arrow). The Nicol is 9x9x25mm.

The knob on the condenser controls the iris.

The condenser has a position marker to precisely orient the Nicol, and the plane of polarization of the transmitted light.