Transmission spheres more than just a reference surface

The importance of understanding the design and use of Fizeau transmission spheres, for accurate evaluation of surface irregularities, cannot be understated. There are several characteristics that have a significant impact on the interpretation of the resulting data. Specific tests can be performed on a routine basis to quantify and maintain calibration of the precision masters and as a result, errors attributed to the transmission sphere can be isolated. The overall goal is to obtain accurate evaluations of surface irregularities of the actual surface under test.