Lens (optics) divergence of a collimated beam, it does alter the width of the beam. The magnification of such a telescope is given by which is the ratio of the output beam width to the input beam width. Note the sign convention: a telescope with two convex lenses ("f" > 0, "f" > 0) produces a negative magnification, indicating an inverted image. A convex plus a concave lens ("f" > 0 > "f") produces a positive magnification and the image is upright. For further information on simple optical telescopes, see Refracting telescope § Refracting telescope designs. Cylindrical lenses have curvature in only
Crepuscular rays Crepuscular rays Crepuscular rays (more commonly known as sunbeams, sun rays, splintered light, or god rays), in atmospheric optics, are rays of sunlight that appear to radiate from the point in the sky where the Sun is located. Shining through openings in clouds (particularly stratocumulus) or between other objects, these columns of sunlit particulates are separated by darker cloud-shadowed volumes. Despite seeming to converge toward the light source, the rays are in fact near-parallel shafts of sunlight. Their apparent convergence is a perspective effect. This phenomenon mimics the way parallel railway lines or long hallways, for example, seem to seek