"cshake" <cshake+pov### [at] gmailcom> wrote:
> I'm trying to figure out what I should use to create diffusion on a spotlight,
> similar to filters used in photography and theater.
>
> I don't mean the diffusion function in povray itself, but an effect between the
> light source and the target that spreads out the light to create soft edges on
> everything. I already understand how to use the radius and falloff in a
> spotlight source, but all my attempts so far in making a diffusion filter have
> turned out badly.
>
> I've experimented with using a thin glass-textured plate in the light beam and
> using photon refraction effects, with varying the thickness of the object to
> get more and less diffusion. I found that there seems to be a cutoff
> thickness where it either doesn't change the light at all, or makes the light
> so dull that there is no longer a circular beam even at 4 units away. That
> is with changing the intensity of the light to compensate for fading loss.
>
> Does anyone have an idea of how to do this?

By the sounds of it, you want to use area lights, not spotlights.
Spotlights in pov are treated as point lights, but have attenuated edges of the
lighted area, the shadows are still sharp.

Try using an area light but with an open cylinder around it to limit the light
to a spot.  You can effect the amount of soft shadowing by the size of the
light/cylinder, etc.  A while back I posted a method for making a square
spotlight using area lights.  It would probably provide a good starting point.
I'll dig around and see if I can find it.

-tgq

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