# Is there a formula for determining the focal point of a sphere?

I guess this is the same as for cylinders, when light is shone through parallel to the cross-section, but Google-ing this only turns up lenses like the ones used in glasses.

I'm looking for something like what's described in this article: http://spie.org/x34513.xml

I hope to determine the veracity of the equation described there.

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Does this link help? –  Glen The Udderboat Mar 16 '13 at 22:33
DarkLightA: doesn't your own link answer your question? –  Colin K Mar 16 '13 at 22:52
Thanks Gugg! Make it an answer! Colin K, it was the only source I could find, so I was somewhat skeptical. –  DarkLightA Mar 16 '13 at 22:55
Also, is there a way to determine how much will be reflected backwards off a side of a sphere, compared to what passes through? –  DarkLightA Mar 16 '13 at 22:56
I found this (pdf-alert). –  Glen The Udderboat Mar 16 '13 at 23:19

## 1 Answer

At your request. Here's somebody working it out for you.

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Perfect! Thanks! –  DarkLightA Mar 16 '13 at 23:08