Encyclopedia > Dioptre

  Article Content


A dioptre (also diopter) is a unit of curvature equal to one per metre. A circle with radius 1/2 metre has a curvature of 2 dioptres. It is also used to measure focusing power of lenses and (curved) mirrors; the power is the inverse of the focal length. Diverging lenses have negative power.

If the curvature of a lens is C and the index of refraction is n, the focusing power is F=(n-1)C. If both surfaces of the lens are curved, consider their curvatures as positive toward the lens and add them. For a mirror the focusing power is F=2C.

All Wikipedia text is available under the terms of the GNU Free Documentation License

  Search Encyclopedia

Search over one million articles, find something about almost anything!
  Featured Article

... is found in environments. Their root penetrate into the mud[?] or sand of sea floor. It is named after the terrestrial grass for the physical resemblance. The ...