The collimator is an all-spherical refracting design as described above. The collimator focus may change with temperature, and consequently must be capable of focus correction. This may be achieved by passive compensation, by moving some part of the collimator, or by focus of the collimator assembly as a unit.
Focus will be motor-driven, with a range sufficient to correct for thermal focal errors. The collimator assembly is kinematically mounted to the mainframe to avoid stressing the optics and to simplify alignment. The collimator assembly includes features to simplify removal, re-installation, and re-alignment. The lenses are removable from the barrel for re-coating.