Wolfram|Alpha has lens and imaging calculators. Solve problems related to spherical equivalents; field of view; angular diameter; back focal length, with or without a thick lens; front focal length, with or without a thick lens; Gullstrand's or lensmaker's equation; a two thin lens system; two, three or four thin lenses in contact; Prentice's rule; prism diopter calculations; pupillary distance; the Strehl or telescope light‐gathering power ratio; telescope magnifying power; and the thin lens equation.
