A Newtonian reflector telescope is a tube with two mirrors in it. The main, curved mirror is at the bottom of the tube; light comes down the tube, hits that mirror and is reflected back up the tube, towards the second mirror. That one's smaller, flat, and angled at 45 degrees; it ...
Underside of the guider, showing the prisms and part of the relay prism adjustment mechanism (this allows for a wide range of guide star selection). The mounting holes indicated are the attachment points for the lower casting onto the telescope tube: ...