Optical sensors for noncontact velocity measurement require imaging systems with constant optical magnification in spite of the variable distance between the sensor and the object of measurement. This requirement can be met using telecentric systems. When such systems are set up, several design considerations must be taken into account. These concern the decision as to whether a single or a double telecentric system shall be used, as well as the choice of the optical magnification and the dimensioning of the aperture stop. The results of the theoretical analysis are confirmed by experiments with a prototype velocity sensor for belt drives.