Figure 3-9Reflection (a) The angle at which a beam of light strikes a mirror (the angle of incidence, i) is always equal to the angle at which the beam is reflected from the mirror (the angle of reflection, r). (b) A concave, parabolic mirror causes parallel light rays to converge and meet at the focal point. The distance between the mirror and focal point is the focal length. (c) A Newtonian telescope uses a flat mirror, called the secondary mirror, to send light toward the side of the telescope. The light rays are made parallel again by passing through a lens, called the eyepiece. The dashed line shows where the focal point of this primary mirror would be if the secondary mirror were not in the way.