COS made interferometric testing techniques more accessible to the astronomical community, both professional and amateur. The introduction of the Ceravolo interferometer, and kit components required to construct it, made long path difference interferometry accessible to many small optics shops and amateur telescope makers. COS also popularized the Ross null test for testing telescope mirrors. Our precision Reference Element and Ross null lens are back by popular demand.

	Interferometry and Telescopes Learn how to build your own interferometer and use it to test telescope optics.
	Reference Element Back by popular demand! The COS spherical wave interferometer reference element.
	Ross Null Lens Time to toss out that zonal mask! The Ceravolo Ross Null lens eliminates the spherical aberration of a telescope mirror when tested at the center of curvature.
	Using The Ross Null Lens To learn how to perform mirror testing with the Ross Null lens, view or download this PDF document.