Nondistorting lateral edge support of large telescope mirrors.

Simply by push-pull shear action at their outer edge, large circular telescope mirrors can be laterally supported free from bending distortion, if the upright mirror is kept in balance by a cosine distribution of weak axial forces applied at its outer rim and possibly also at the central hole. The flexure-induced comalike wave-front aberration of a thin 8-m meniscus mirror was reduced to an rms value of 0.5 nm over the full aperture; the largest path difference was reduced to 2.4 nm. A comparable result has also been calculated for a meniscus mirror of different geometry and a material with different elastic constants. Realizing such possibilities in practice demands accurate engineering. A helpful artifice is investigated for the correct application of the tangential supporting forces.