What's it about?

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.


When optical components are tested interferometrically with transmission spheres, we assume that the resulting data output is the profile and/or error of the surface under test. This assumption may not always hold true. Based upon the level of test accuracy required, there are certain characteristics needed to evaluate the peak to valley test data.{Note: We have chosen to exclude the details of the interferometer accuracy / precision as well as transmission sphere alignment, which has been covered in subsequent writings.)