Lenses are typically mounted into precision machined barrels and constrained with spacers and retaining rings. The
details of the interfaces between the metal and the glass are chosen to balance the accuracy of centration and axial
position, stress in the glass, and the cost for production. This paper presents a systematic study of sharp edge, toroidal,
and conical interfaces and shows how to control accuracy, estimate stress, and limit production costs. Results are
presented from computer models, finite element simulations, and experimental testing.