The Abbe condenser is located below the stage on a threaded brass arm. Focusing is via the standard pinion gear (B). There is an additional rack and pinion (A) for translating the iris assembly; that, along with rotation, allows centering the lower iris diaphragm.
The condenser has two diaphragms: A: the Abbe-type below the condenser, and B: a hemispherical iris above the condenser (C). This iris can function only if the condenser lens assembly is removed from the optical path.
Condenser focus rack. The hole at the bottom is the mirror assembly insertion point. The mirror is missing.