Focus is via Rack & Pinion, with the rack (arrow) machined into the rear face of the stage and mirror support shaft (B). Focusing the sample moves the stage.
The microscope body is screwed into a cantilever (arrow) at the top of the main support shaft (A). Attached to the cantilever at the top and the main shaft at the bottom is a square shaft (B) to which the stage (C) and mirror (D) assemblies are attached.