AS101 Lecture Notes - Reflecting Telescope, Spectroscopy, Thin Lens
Document Summary
Light rays can be reflected (bounced off) or refracted (bent) at an interface. If the surfaces are close, we have a thin lens. A lens has usually two refracting surfaces. Refraction can cause parallel light rays to converge to a focus. The focal plane is where light from different directions comes into focus. The image behind a single (convex) lens is actually upside down. Refracting telescope: focuses light with lens (galileo: need to be very long, to maximize the distance between the lenses, they have large, heavy lenses for good light collection. Reflecting telescope: focuses light with mirrors (newton: reflecting telescopes can have much greater diameters, modern telescopes (built after 1900) are reflectors. Only the reflecting surface of mirrors in a reflecting telescope have to be perfectly shaped. In a lens the entire shape of the lends and both surfaces are important. Objective lenses are heavy and difficult to stabilize at the top of the telescope.
