A method of testing a convex mirror surface figure in which an optical quality substrate material is used having a convex front surface and a rear surface polished to a precise optical figure to create a lens. The lens is then tested by a standard interferometric or wavefront lens-testing method and the convex surface coated once a desired curvature is obtained. Null testing may be attained by passing a collimated interferometer beam through a focusing lens shaped to counter the predicted spherical aberration introduced by a perfect convex mirror/lens. A nominal rear surface figure of the mirror/lens may be used if a precisely figured test window is contacted with the rear surface using a refractive index-matching substance with an index of refraction closely matching the index of refraction of the test optic.