Flexures are passive mechanical-structural devices used to isolate optical elements from the mechanical and thermal effects of the structural support system in such a way that these effects on optical instrument quality are minimized. Mechanical effects include gravity, and inertial and vibratory loadings, as well as possible stresses resulting from assembly errors. Thermal effects include both steady-state and transient environments. For example, if an optical device, with a mirror or lens having a coefficient of thermal expansion orders of magnitude less than that of the material of the support structure (e.g., steel or aluminum), is assembled at a given temperature but operates in a thermally different environment, the optical quality of the instrument may degrade very significantly unless the mirror or lens is isolated from the thermal strain of the support structure. Normally, the mechanical precision of the mount is much less than the precision of the optical surface of the element. If the optical element is rigidly clamped to the mount, this lack of precision in the mount may distort the optical element, and degrade the optical quality of the element.