Mirau type interferometers are widely used for the evaluation of surface structures of small areas since complete Mirau objectives are available on the market. The remaining adjustment effort to make an instrument is within limits since the interference comes into existence inside the objective and this also makes the instrument pretty stable. On the other hand this means that instruments using the Mirau objectives have pretty similar characteristics at least as far as those parameters which seem important for the fidelity of the measurement like aperture, magnification, stand off, fringe contrast, stablity of the fringes, measurement area.

For those requirements which cannot be met by the Mirau objectives one needs to develop devices using a different principle, e.g. Michelson, Fizeau, MachZehnder, Linnik, etc. Widely used and reasonably easy to make is an instrument using the Michelson principle. The separation of the illuminating light beam into the object and reference beam is done directly in front of the object. When utilising large lenses one can achieve relatively large measurement areas. The required phase shifting can be done via the reference mirror. But not only instruments having large measurement areas can be designed but also such ones having comparable measurement fields like the Mirau type but with dimemensions adapted to the measurement task, e.g. surface structure measurement inside bores the diameter of which is smaller than the length of the Mirau objective.