  The Simons Observatory will consist of a single large (6 m diameter)
telescope and a number of smaller (0.5 m diameter) refracting telescopes
designed to measure the polarization of the Cosmic Microwave Background to
unprecedented accuracy. The large aperture telescope is the same design as the
CCAT-prime telescope, a modified Crossed Dragone design with a field-of-view of
over 7.8 degrees diameter at 90 GHz. This paper presents an overview of the
cold reimaging optics for this telescope and what drove our choice of 350-400
mm diameter silicon lenses in a 2.4 m cryostat over other possibilities. We
will also consider the future expandability of this design to CMB Stage-4 and
beyond.
