This instrument has two objective lenses, one (A) placed in the hardwood collar and another (B) mounted in a wooden ring.
The second lens (B) is probably a lower magnification replacement for lens A. However, it is unclear how to remove A and replace with B. An alternate possibility is that A and B were used together. This increases the total magnification, however places the front and back focal planes so close to the lens that it is impossible to focus the sample.

A: Dia=7mm, f=5mm
B: Dia=7mm, f=10mm

The objective assembly press-fits into the hardwood base of the microscope.
The user looks into this end of the instrument.