Myślę,ze tutaj jest trochę wyjaśnień odnośnie 'mirror coating', tak, ze po czesci masz racje ale generalnie w drogich"dachówkach" pokrywa się je warstwami celem głownię zminimalizowania refleksów no bo jak piszą transmisja odbicia i tak jest na poziomie 100%
https://baltimorebirdclub.org/choosing_optics2015.pdf
Another surface on the Schmidt prism in the commonly used Schmidt-Pechan roof prism set needs a reflective mirror coating
similar to the reflective coating on the mirrors in your house, to keep the light going along the path. While the mirrors in your house probably use aluminum, which reflects about 82%
of the light, a more expensive silver coating can reflect 87% -92% of the light. Stepping up in price, one can get a more expensive oxygen-free “HR” coating of either aluminum
or silver –the extra steps to keep oxygen away make the metal surface brighter, reflecting about 88 –90% for the HR process aluminum coating, or 97 –98% with the HR process silver.
still more expensive di-electric chemical multi-coating, with alternating layers of material of high and low refractive index, up to64or 70carefully placed layers, can reflect over 99% of light across the visible spectrum.
For a price.
Note that all these mirror coatings are for Schmidt Pechan roof prism binoculars only; porro prisms and Abbe Koenig roof prisms already reflect 100% of the light at all reflecting surfaces and don’t need a mirror coating, and the porro prisms don’t need a phase correction coating. a wiec raczej nie będzie "kresek" na jasnych gwiazdkach...
They all can still use the anti reflective multicoatings where the light goes in and comes out
a tu wyjaśniają dlaczego i tak się pokrywa warstwami :
All of these various coatings are used to
*increase the light transmission efficiency of the binoculars, to yield a brighter,
*clearer image with less light getting lost along the way.
*more money will usually get better coatings and more light getting through the binoculars to your eyes with a brighter image with higher contrast.