(1) Slip the focusing tube spacer and the lower adapter collar onto the trinocular tube. 
(2) Insert the microscope ocular of your choice into the trinocular tube.

3) Slip the right angle unit onto the lower adapter collar until the microscope ocular rests directly against the surface of the mirror.

(4) Tighten the set screw on the bottom of the right angle adapter so that the lower adapter collar is held in place.