All three telescope designs have two main parts, a tube assembly that holds the optics and a mount to support the tube assembly. Jason Ware Inside a Reflecting Telescope Place a reflecting telescope beside a refractor, and you'll notice some major differences. The front of the reflector's tube is wide open. Despite these differences, the reflecting telescope weaves the same optical magic on starlight that a refractor does. The refractor works by collecting incoming light with a convex objective lens and concentrating the light to form a small, upside-down image.
Light passes through the open end of the tube, travels down, and strikes the objective mirror.
It's then reflected and concentrated to a point where a small upside-down image is formed. The distance between mirror and image is the mirror's focal length . The more highly curved the mirror, the shorter the focal length. Last time, we explained how to demonstrate to youngsters the image formed by the objective lens of a refracting telescope. Your best bet for an objective mirror substitute is a circular shaving or make-up mirror.