This is a "5a". Made out of copper, bronze and steel, so very heavy.
Note that the inscription says: P.Rbl. in stead of the official designation Pz. You find this on more pieces of optic. The handles provide a quick change of the mirrorhead.
This is a "5", complete with the supporting bar which was fixed on the floor in the cupola.
Peeping through the glass.
The arrow follows the angle of the head outside. A fine piece of technology.