  Calcite is a uniaxial, birefringent crystal, which in its optically
transparent form, has been used for animal eye lenses, the trilobite being one
such animal. Because of the calcite birefringence there is a difficulty in
using calcite as a lens. When the propagation direction of incoming light is
not exactly on the c-axis, the mages blur. In this paper, calcite blurring is
evaluated, and the non-blurring by a crystallin eye lens is compared to a
calcite one.
