13: Parabolic and flat mirror set two
After passing the polarizer remains to focus the light beam back and align it with the camera that is mounted on the outside of the cabinet.
The parabolic mirror to the right and the plane mirror (tilted) to the left.
Also here, an off-axis parabolic mirror.
See it as a mirror in a Newtonian telescope where only a small circular outer part of the mirror is used.
The great advantage of this is the output light beam from the mirror is not in the same direction as the incoming.
It's folded and save a lot of space.
A major drawback is that the optics imaging becomes more deformed than the normal parabolic mirror which already severe coma.
But you can not get everything, but choose the one that is most optimal for what you want to achieve.
Using mirrors instead of lenses also means that the instrument can handle a wider range of wavelengths.