optics - 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.

Answer

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