Abstract: At a flight trajectory measuring and observation theodolite there is mounted between two spaced housings a telescope and additionally laterally at the housings further optical devices and by means of a motor driven shaft can be pivoted about a common elevational axis. For the stress-free mounting of the shaft which is fixedly connected for rotation with an inner ring or race of a roller bearing, the outer race or ring thereof is connected by means of a flange portion with a wall. This wall, viewed in axial direction, is provided with at least three radially effective spring elements and the wall is radially inwardly directed and provided with an opening. The spring elements separated by a slot are uniformly distributively arranged at the circumference of the opening and are bounded by an arc corresponding to the inner surface or side of the opening, the center of such arc being located at the axis of rotation of the shaft.