Keywords: foucault tester knife edge tester knife-edge tester ronchi tester caustic tester ronchi caustic mirror making telescope catadioptric newtonian gregory schmidt cassegrain parabola sphere testing apparatus dial indicator micrometer slit radius of curvature focal length autocollimation polishing mirror maker pitch lap cerium oxide amateur telescope maker zones test mask grinding grit micron powder wet grinding stand tool plate glass pyrex astro sitall astrositall sagitta abrasives silicon carbide pitch squares optics testing equipment pinhole testing and correcting turned edge oblate spheroid ellipsoid paraboloid hyperboloid figuring waves mirror correction making pitch squares shadows lens lense secondary primary effective focal length shadow appearance inside focus outside focus zonal measurements light beam light source dog biscuit spider web stroke length grinding stand concave convex mirror blanks turned down edge turned up edge shadow test spherical aberration wavelength of light collimation baffle tubes maksutov gregorian meniscus reflecting refracting light rays coma astigmatism curvature of field distortion mirror blanks mirror making kits razor blade upper curve lower curve paraboloidal curve centre zone image shadow patterns cone of light correction curve measured curve hyperbolic edge eliptical edge ellipsoid oblate edge central hill aspherized radius testing spherometer