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On-machine metrology is particularly important for diamond turning and grinding as it is difficult to remount and align a part if it does not meet off-line inspection criteria. There is also the issue of tool wear; a process that started well may fail part way through the cut, and if tool replacement is needed, it is vital to know that before removing the part. A means of rapid, non- contact, in situ profiling and roughness measurement could improve the productivity of diamond tool machining.

Measuring surface roughness or finish is one the more difficult measurements to make on large mirrors or lenses. In general, the measurand is too large to place on the stage of a surface- roughness measuring microscope, so an indirect measurement must be made using replicas. The long mechanical path between interference objective and sample on traditional microscope based profilers make these instruments prone to vibration due to the environment which disturbs temporal phase shifting measurements.

The MicroFinish Topographer (MFT) is the result of an interest in directly measuring the surface roughness of large optics without the need for using replicas that may degrade the measurement data and that contaminate the surface. Once the MFT proved itself on large optics it was immediately suggested that a similar device should be designed for small optics. All this really took was turning the original MFT upside down and placing small specimens on a holder. This one device tests samples from 10 mm diameter to 10 m with phase measuring interferometry that does not need vibration isolation. Further, the MFT form factor makes it ideal for use in doing on-machine surface finish metrology.

Several examples are given of optics apparently specified only by figure and finish. Although these optics met the specifications they did not produce good images. The presumed reason for the poor performance was the lack of a specification for mid-spatial frequency roughness. We show that a reasonable specification can be applied using the concept of a structure function, a mathematically simple function easily calculated from interferometric phase data at each pixel. An example wavefront is used to show how the specification can be developed from typical figure and finish specifications and include information about roughness in the mid-spatial frequency region.

The Rayleigh Rice vector perturbation theory has been successfully used for several decades to relate the surface power spectrum of optically smooth reflectors to the angular resolved scatter resulting from light sources of known wavelength, incident angle and polarization. While measuring low frequency roughness is relatively easy, the corresponding near specular scatter can be difficult to measure. This paper discusses using high incident angle near specular measurements along with profile generated surface power spectrums as a means of checking a near specular scatter requirement.