Main Question or Discussion Point
I recently came across the Bris-Minisextant(wwwdotcassens-plath.de/catalog_web/096e_webdothtml) while researching sextants in general. While not truly a sextant in the conventional sense the device caught my attention and I started looking into what might be its underlying physical principle. This has brought me to the conclusion that it must be a variation of a Fabry-Perot Interferometer. I'm wondering if someone on the forum can confirm that this is in fact the basis of the device. I'm also trying to understand what controls the number of reflected images that one sees in the device. I'm tending to think that it has to do with the refractive index of the materials and/or reflectivity of the surfaces involved but if so I don't understand the relative influence of each. In the Fabry-Perot Interferometer the reflecting surfaces are intended to be parallel and in the Bris sextant they are of course at a definite angle. Varying the value of the angle doesn't change the number of images, only their relative separation. Any further information about how this device works (in the optical sense) is appreciated.