Bi-concave lens is a simple lens or lens shape within a compound lens , whose surfaces curve toward the optical center. Such a lens causes light rays to diverge. Bi-convex lens is a simple lens shape whose surfaces curve outward, away from the optical center. Such a lens causes light rays to converge. Binocular vision is the visual ability to determine three dimensions.
Stereoscopic photography depends on the use of binocular vision.
Bi-pack is a combination of two films, differently sensitized, but exposed as one. Bi-refringence is the splitting of light passing through certain kinds of crystals into two rays at polarized right angles to each other. Bispheric lens is a lens having different curvatures at the center and the edge, each of which forms part of a sphere. The different edge curvature brings the peripheral rays more closely to the same point of focus as the center rays. Bitumen is a hydro-carbon which hardens by the action of light.