optics ro adapted for example to a conical object surface test object o may be imaged onto image recorder ba in some instances via intermediate images zw zw 2 and superimposed with the reference wave to obtain the contour elevation of surface features information mirror sp 2 is scanned over the measuring area high interference contrast may occur in the image of test object o when the path difference between the two mirrors sp 1 and sp 2 is precisely the optical path difference between reference mirror rsp and test object o to obtain the 3d contour profile elevation of surface features established methods may be used to analyze the interferograms in each image point a benefit of this design may be that the object and reference waves propagate through virtually the identical optics assembly so that aberrations may be substantially compensated for moreover this set up may be more rugged and therefore less susceptible to mechanical shocks furthermore as shown in fig6 and 7 modulation interferometer mi is coupled to probe interferometer si via a fiber optics fo this may be equally possible via free space optics alternatively the optical path length in reference arm ra may also be changed by acoustooptic modulators scanned through compare german published patent application no 197 21 842 as a further exemplary embodiment the common path interferometer may be implemented in the mirau set up also without modulation interferometer mi light source sld may then be coupled directly into probe interferometer si e g via beam splitter st 2 in accordance with fig7 for the depth scanning the actual reference mirror must then be moved toward the beam splitter fig7 depicts reference mirror rsp.