Interference fit equations for lens cell design using elastomeric lens mountings

Abstract

Optical designs often consist of lenses that are mounted in a common lens barrel. For lenses having diameters greater than 20 cm and subject to large temperature differentials and/or shock loading, standard metal retainer ring mountings may not be acceptable. An alternate method for mounting these lenses is to mount each individual lens in its own subcell using an adhesive and then to use an interference or press fit to mount these subcells in the lens barrel. When mounting lenses in this manner, it is necessary to evaluate the stress induced in the glass and the residual difference in the optical path. A closed-form analytical derivation was made for a simple lens mount that relates the allowable magnitude of the interference fit to the stress in the glass. This theoretcal expression was then modified using finite element models for use with complex lens designs. Moreover, since lens mountings may require the use of relatively thick layers of flexible elastomer to mount the lenses in their individual cells to prevent large thermal and/or mechanical stresses, the equation for determining the decentration of lenses mounted in circumferential flexible elastomers is also derived. The theoretical expression was used to verify finite element models that then may be used for more complex mounts.