Astronomy
My 10 inch Mirror with a 1/48 P-V Wavefront Error @ 550 nm My Mirror's size was on the cusp of the "thickness Solution" to Sagging.  Consequently it was quite massive due to its required thickness.  At that time there were no standard sized mirror blanks or "Telescope Mirror Kits". I had to order my blanks from Corning Glass Works by specifying the grade of glass, diameter and thickness required.
Recently, another option has become available to amature telescope makers in the form of more advanced "floatation type" Cells that support the Main Mirror at many computer-optimized points to reduce the sagging.  Professor David Lewis of the University of Toronto has developed a CAD program called "PLOP" enabling anyone to design this type of Mirror Cell.  These cells permit larger aperture, short focal length mirrors to be made that will hold their curve within acceptable limits.
Forty years ago I discovered a flaw in the traditional method of figuring a Parabolic Mirror, and devised a better method, - enabling me to make a telescope mirror that surpassed all others of its size in quality.  Today, that mirror still has no equall, - and I am entering the Telescope Manufacturing buisness where I can offer a vastly superior product because of my improved method.  Since then I have learned to make flat Secondary Mirrors of matching quality.  This means I can offer complete Newtonian Telescope Systems with a Wavefront Error 3 orders of magnitude better than Difraction Limited Optics.  The reduction in system quality is due to the fact that Wavefront Errors are cumulative. A third optical component of the same quality would reduce the system quality to a magnitude only twice as good as Difraction Limited Optics.