Quick answer
Focus on wavefront quality, f/# match to your test part, and aperture size. A Zygo Certified Transmission Sphere like the 4" F/0.75 offers verified low wavefront error, often better than λ/20.
Why wavefront quality matters more than price
Zygo Certified parts are individually tested and documented, so you get a known wavefront error — often λ/40 PV or better — without paying for a new unit. The certification reduces measurement uncertainty in your interferometer setup.
A lower wavefront error (e.g., λ/40 vs λ/20) directly improves the accuracy of surface form measurements on your test optics. For critical applications like lens fabrication or optical assembly, this difference can be decisive.
f/# and aperture: matching your test part
The transmission sphere's f/# must match the numerical aperture of your test surface. An f/0.75 sphere covers a steep cone angle, suitable for fast optics or short radius spheres. Using too slow a sphere on a fast part will clip the beam and cause measurement errors.
Aperture diameter (e.g., 4") determines the maximum part size you can test. If your parts are larger than the sphere's clear aperture, you'll need a different setup or stitching.
Compatibility with your interferometer
Zygo transmission spheres use a standard threaded mount compatible with most Zygo interferometers, including Verifire models. However, always verify the interface type — some older systems may require an adapter.
The 4" Verifire SV, for instance, accepts a 4" transmission sphere directly. If you're upgrading from a smaller aperture, check that the interferometer's beam expander can fill the larger sphere.
Frequently asked questions
What does Zygo Certified mean for a transmission sphere?
It means the sphere has been individually tested and meets Zygo's published wavefront specification (often λ/20 PV or better). Certified parts come with documentation of actual measured performance.
Can I use any f/# transmission sphere on my Verifire SV?
Yes, as long as the aperture size matches (4" for a 4" Verifire SV) and the f/# is appropriate for your test part. The Verifire SV accepts standard Zygo threaded transmission spheres. Always verify the mechanical interface before purchasing.
How do I choose between λ/20 and λ/40 wavefront?
For general shop-floor testing, λ/20 is sufficient. For certification or high-accuracy metrology, choose a sphere with λ/40 or better. The cost difference is usually small compared to the improvement in measurement confidence. Match the sphere's wavefront to your measurement tolerance.
Is a used Zygo Certified sphere a good value?
Yes, because certification confirms performance regardless of age. A certified used sphere can save 30-50% vs new while delivering the same or better wavefront quality. Check the certification date and documentation.
Product facts
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4" , F/0.75 Transmission Sphere: Zygo Certified 4" F/0.75 Transmission Sphere, serial 250036, λ/20 PV, close to 1/40th wave. This sphere delivers wavefront error well below λ/20, reducing measurement uncertainty for high-precision optical testing.
4" , F/0.75 Transmission Sphere
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4" Verifire SV: 4" Verifire SV interferometer, upgraded with new camera, electronics, and laser. Fully compatible with a 4" transmission sphere, this system provides a modern, reliable platform for interferometric measurements.
4" Verifire SV
