Camera lens that blocks most rays of light, ideally selecting one ray to the object for each point on the image sensor. Pinhole lenses have a few severe limitations: Practical lenses can be thought of as an answer to the question: "how can a pinhole lens be modified to admit more light and give a smaller spot size?". A first step is to put a simple convex lens at the pinhole with a focal length equal to the distance to the film plane (assuming the camera will take pictures of distant objects). This allows the pinhole to be opened up significantly (fourth
Anticrepuscular rays Anticrepuscular rays Anticrepuscular rays, or antisolar rays, are atmospheric optical phenomena similar to crepuscular rays, but appear opposite of the Sun in the sky. Anticrepuscular rays are nearly parallel, but appear to converge toward the antisolar point due to linear perspective. Anticrepuscular rays are most frequently visible around sunrise or sunset. Appearing to radiate from the Sun, crepuscular rays usually look much brighter than anticrepuscular rays. This is because the atmospheric light scattering making the crepuscular rays visible occurs at low angles to the horizon (see Mie theory). Although anticrepuscular rays appear to converge toward the antisolar point, the convergence