Peter Popov wrote:
>On Thu,  1 Aug 2002 16:12:08 EDT, "Don Barron" <ani### [at] ukonlinecouk>
>wrote:
>
>>I've tried unsuccessfully to make scenes containing a lens focussing a point
>>light source show the rays in a scattering medium.  Does anyone have a
>>worked example in a pov file to help?
>
>How would you calculate the focal distance of the lens? I know it is
>possible, but I don't know how.
>
>
>Peter Popov ICQ : 15002700
>Personal e-mail : pet### [at] vipbg
>TAG      e-mail : pet### [at] tagpovrayorg
>

If the thickness of the lens is thin, I think the equation is
1/f = (n-1)*(1/r1+1/r2)
implying
f=1/{(n-1)*(1/r1+1/r2)}
where f is the focal length, r1 and r2 are the radii (sp?) of the spheres.
Tony

ton### [at] xenomechanicscom

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