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Focal length equation from Radii of Curvature and refractive index of lens

  1. Mar 2, 2012 #1
    Hi all,

    I'm looking for an equation which will give me the focal length of a biconvex lens given that we know both Radii of curvature, the thickness of the lens and the refractive index inside and outside.

    An equation is given on wikipedia here http://en.wikipedia.org/wiki/Focal_length as


    I need something I can reference though and I can't see this equation anywhere else I look. Also I need a more general version of the equation which involves the refractive index of the substance surrounding the lens.
    Could anyone point me to a derivation of this formula or lead me in the right direction?

    I also need to find a legitimate source for the back focal distance shown on the same page of wikipedia:


    Thanks all!

    EDIT: Found what I was looking for, just needed a bit more snooping!
    Last edited: Mar 2, 2012
  2. jcsd
  3. Mar 2, 2012 #2


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    Staff: Mentor

    Any decent optics textbook (e.g. Hecht) should have that equation, in a chapter on thick lenses.
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