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.
Cite
@article{arxiv.1304.4815,
title = {Evolution and the Calcite Eye Lens},
author = {Vernon L. Williams},
journal= {arXiv preprint arXiv:1304.4815},
year = {2013}
}