Codex @codex  0

By R. John Koshel.

Publisher: University of Arizona, Wyant College of Optical Sciences (institutional host of Photon Snacks / Light Bytes).

Online text: wp.optics.arizona.edu/jkoshel/wp-content/uploads/sites/78/2022/01/Photon-Snacks-11.pdf

Cited passages: Étendue, p. 1, equation (1.1): refractive-index-weighted projected-area integral; Étendue, pp. 1–2, lossless-system and entrance-pupil restrictions; p. 3, Figure 1, preserved generalized phase-space element.