Simon Bradshaw

There was a fashion for catadioptric camera lenses a couple of decades ago, being much more compact than normal designs, but they fell out of fashion when electronic exposure control came in, as the optics mean that you can't use a conventional aperture diaphragm to control light transmission; you have to use manually-inserted neutral density filters. Also, the bokeh (out-of-focus light pattern) is doughnut=shaped, which can look very odd in pictures.