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How to Easily select the best transmission sphere 


Interferometric testing requires two matched optics: the optic under test and a reference. When measuring spherical optics, the reference is a spherical surface with roughly the same curvature as the surface under test. The housing that contains the focusing lenses and reference surface is called a transmission sphere (t-sphere, or TS).

This application note discusses:

  • the calculations required to determine the correct transmission sphere to use to test a given optic
  • the percentage of clear aperture that will be measured
  • whether proper test optic focus can be achieved

This information will help you to select the best spherical reference optic for a particular test optic.



Fizeau Interferometers

A Fizeau interferometer is a laser interferometer configuration commonly used for measuring the surface shape and transmission quality of optics and optical-grade surfaces. 

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