The rays are then reflected back up through the telescope tube toward the focal point. In a Newtonian reflecting telescope, light rays from distant objects, which are essentially parallel (because they come from so far away), strike the concave main mirror at the same angle. Newton used a concave spherical mirror to make his reflecting telescope, a design that is still popular with amateur astronomers due to its simplicity, low cost and high degree of image quality. The radius of curvature of a mirror determines its magnification factor and its focal length. This generally produces a magnifying effect, such as that seen in a makeup mirror. If the surface is concave, or curved inward, a group of light rays from a distant source is reflected back toward a single location known as the focal point. These mirrors are often used for outside rearview mirrors on cars and for keeping large areas under surveillance in stores. If the mirror is convex, or curved outward, it will reflect a wider area, in which images appear smaller and farther away than those from a flat mirror. The most common curved surface used in optical devices is a spherical mirror. However, if the surface of the mirror is curved, the angles of reflection are different at different points on the surface. This happens because the light rays change direction when they go from one transparent material (air) into another (water). For example, when you look at a spoon in a glass of water, the submerged part of the spoon appears to be in a different place than expected. The third law governs how light rays behave when they pass between two different media, such as air and water. The second states that when a light ray encounters a smooth, shiny (or conducting) surface, such as a mirror, the ray bounces off that surface. The first law states that light rays move through similar transparent media in straight lines. Geometric optics treats light as continuous rays (as opposed to waves or particles) that move through transparent media according to three laws. (The other class is physical optics.) Geometric optics Geometric optics is one of two broad classes of optics, the field that "deals with the propagation of light through transparent media," according to Richard Fitzpatrick, a professor of physics at the University of Texas at Austin, in lecture notes for a course in Electromagnetism and Optics. The reflection of light rays is one of the major aspects of geometric optics the other is refraction, or the bending of light rays.
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