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  1. #1
    bvy
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    Focal Length Question

    What would be the focal length of a hemispherical (half ball) lens of radius r? I'm only finding details related to ball lenses and plano-convex lenses. Thanks.

  2. #2
    Leigh B's Avatar
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    A hemispherical lens is just a plano-convex lens of appropriate dimensions (disregarding distortion & aberrations).

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  3. #3
    bvy
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    I see. The lensmaker's equation with radius of curvature of zero (?) for the flat side and, and r for the hemispherical side. I just need to find the refractive index of clear acrylic.

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    Leigh B's Avatar
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    Quote Originally Posted by bvy View Post
    I just need to find the refractive index of clear acrylic.
    Google it.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

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    Helen B's Avatar
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    Quote Originally Posted by bvy View Post
    I see. The lensmaker's equation with radius of curvature of zero (?) for the flat side and, and r for the hemispherical side.
    The radius of a flat surface is infinite, not zero (so the reciprocal of the radius is zero). You may be better off using Gullstrand's equation for a thick lens rather than the lensmaker's equation, which is only intended for thin lenses.

    Best,
    Helen

  6. #6
    bvy
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    Thanks Helen. I knew there were a few equations, and I think that's the one I need. (And, yes, I was actually referring to the reciprocal term in the lensmaker's equation. I misstated that.)



 

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