The invention relates to an interferometer system (41), especially for use in a co-ordinate measuring system. Said interferometer system comprises, disposed in an illumination beam path, a pair of spaced-apart boundary surfaces (52, 53). A boundary surface (53) facing an object (9) is arranged in a detection beam path, a detector (61) being additionally disposed in said detection beam path. The invention also relates to an interferometer system, especially one of the above-described type, which is provided with a speed indicating system for detecting a relative speed between the test head and the object. A frequency filter of the interferometer system is adjusted depending on the relative speed.