Select Page

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. 

Twyman-Green Interferometers


PhaseCam MWIR Twyman-Green Dynamic Infrared Interferometer

A Twyman-Green interferometer is a laser interferometer configuration used for measuring the surface shape and transmitted wavefront quality of optical components, assemblies, systems, and optical-grade mechanical surfaces.

See 4D Technology at SPIE Photonics West 2022

4D Technology will be attending SPIE Photonics West 2022 in San Francisco, California. The 4D Technology booth will display the AccuFiz D, PhaseCam, and NanoCam HD (while mounted on a robot!), all making measurements live on the show floor.


Get In Touch

(520) 294-5600


3280 E Hemisphere Loop, Ste 146
Tucson, AZ 85706


Office Hours (Arizona Time)

Mon: 8am - 5pm
Tue: 8am - 5pm
Wed: 8am - 5pm
Thur: 8am - 5pm
Fri: 8am - 5pm
Sat: Closed
Sun: Closed

Send a Message

Products of interest:
SubmitSubmit Submitted