4" , F/0.75 Transmission Sphere

I was a little worried about surface quality for this price, but the Zygo certification data shows it's better than 1/40th wave, which is impressive. Fits my interferometer perfectly for testing fast optics.

Got mine today and the certification paperwork shows it's performing well under the stated λ/20 PV, which is exactly what I needed for my interferometer setup. The protective coating is in pristine condition and the housing feels solid.

I needed a high-quality transmission sphere for aligning a collimator and this one is clearly well cared for. The F/0.75 aperture gives a nice tight focus, and seeing it’s Zygo certified with such a clean surface makes it hard to beat.