Germany was the earliest adopter of scoped rifles in World War One, and produced more of them over the course of the war than any other power. After an initial stop-gap effort to scrounge up civilian hunting rifles, a sniper conversion program was adopted by the main German rifle factories. Germany was a world leader in optics production at the time, and so at least 10 different manufacturers provided scopes for military use. Each pattern of scope was unique, and fitted to its own specific mounting bases.
In general (and particularly early on), the Prussians tended to prefer 3x magnification, left-offset scopes with 100-1000 meter range adjustment. The Bavarians, on the other hand, opted for 4x scopes (more magnification but less field of view) that were center-mounted and had range dials marked for 200, 400, and 600 meters. These preferences were never absolute though, and tended to blur as the war progressed.
This particular rifle was originally a sniper, but I believe it was originally fitted with a 3x Voightlander optic. It is currently fitted with a 3x Oigee that has been unfortunately renumbered and mounted on what appears to be a reproduction rear base.