Presentation on Lenses Lenses are made of transparent

Presentation on Lenses

Lenses are made of transparent materials, like glass or plastic, that typically have an index of refraction greater than that of air. Each of a lens’ two faces is part of a sphere and can be convex or concave (or one face may be flat). Convex (Converging) Lens Concave (Diverging) Lens

If a lens is thicker at the center than the edges, it is a convex, or converging, lens since parallel rays will be converged to meet at the focus. A lens which is thinner in the center than the edges is a concave, or diverging, lens since rays going through it will be spread out.

Lenses: Focal Length • Like mirrors, lenses have a principal axis perpendicular to their surface and passing through their midpoint. • Lenses also have a vertical axis, or principal plane, through their middle. • They have a focal point, F, and the focal length is the distance from the vertical axis to F. • There is no real center of curvature, so 2 F is used to denote twice the focal length.

Ray Diagrams For Lenses When light rays travel through a lens, they refract at both surfaces of the lens, upon entering and upon leaving the lens. At each interface the bends toward the normal. (Imagine the wheels and axle. ) To simplify ray diagrams, we often pretend that all refraction occurs at the vertical axis. This simplification works well for thin lenses and provides the same results as refracting the light rays twice. • • F 2 F Reality • F 2 F • • • F 2 F • 2 F • F Approximation