AlexLens wrote:
> Hi all,
> 
> I'm playing around with POV-Ray to make two plano-convex lenses, at fir
st with a
> CSG intersection, and then with numerically calculated data points rota
ted with
> a quadratic spline lathe.
> 
> The problem I'm having now is the plano-convex lens made from a sphere
> intersected with a plane converges light as expected:
> 
> Image 1)    http://img193.imageshack.us/i/planoconvexjpg.jpg/
> 
> But then when I make the lens with a lathe of 1000 data points, it actu
ally
> DIVERGES light, when it should be functionally the same:
> 
> Image 2)   http://img507.imageshack.us/i/planoconvexnumericallin.jpg/
> 
> Here is the POV-Ray source code for the first image (CSG intersections)

> 
> The code for Image 2 is the same as Image 1 except with a lathe with qu
adratic
> spline replacing the CSG intersection.
> 
> Please let me know what you all think could be the reason for this, and
 any
> random tips as well as I'm pretty new to POV-Ray.
> 
> Thanks!!!
> 
	Making a lens out of a lathe works very poorly. The reason is that
none of the available spline types will give you a G2-continuous [*]
connection on the control points. However G2-continuity is essential
to optical surface design.

	Since most lenses are modeled with polynomials anyway, I would
advise you to use an isosurface with the corresponding polynomial.

		Jerome

[*]
http://en.wikipedia.org/wiki/Geometric_continuity#Geometric_continuity
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