Focus knob A separates the upper body tube from the lower objective tube. The dovetail cutout accommodates additional devices inclusing a Bertrand lens for conoscopic investigation or the "Comparator of Mr. Michel Lévy" (a First Order Red Plate).

The upper body tube has fine (A) and coarse (B) focus.

The lower body tube has a coarse (C) and fine focus mechanism (D).

Coarse focus B and C are rack & pinion mechanisms. Fine focus A and D are fine-thread screw mechanisms.

The other visible knobs control X and Y stage movement.