|Leica IIIb (with Summaron 35mm). Picture by Mikel Parial. (Image rights)|
The Leica IIIb by Leitz is an upgrade of the Leica IIIa. It mainly differs by the position of the viewfinder and rangefinder eyepiece, which are separated by a few millimetres on the IIIa and are closer together on the IIIb. The diopter correction lever for the rangefinder has accordingly moved to a different location under the rewind knob.