Hi folks!
    	    	    	    	
Need help in understanding the 'photons{ }' directive...

The Scene:

  A light source & camera (but of course)
  A diamond-CSG-object, transparent, some reflection, lots of IOR
  A box-object, no IOR, no reflection (surface on which diamond rests) 

If I understand the manual correctly, all surfaces will show photon
caustics by default.

Therefore:

   The box should not need a 'photons{}' directive.
   The diamond should have a 'photons{ target refr on refl on }'

I'm not quite sure if the diamond itself should have a 'collect off'.

From what I gather, all light entering a diamond's crown comes back
out through the crown.  Since the light has bounced at least twice
inside the diamond before leaving again, I believe caustics are in order
therefore the 'collect off' should not be applied to it (what are your
thoughts here?) 

The target keyword...

passsage from the manual:
  
  The density of the photons can be adjusted by specifying the
  spacing_multiplier. If, for example, you specify a spacing_multiplier
  of 0.5, then the spacing for photons hitting this object will be 1/2
  of the distance of the spacing for other objects.

Generally I have seen more photons collected with target .8 rather than
with target .4, should it not be the reverse? 

All input and comments will be appreciated.

Thanks

-- 
(MIKA) Marc Champagne
marcch.AT.videotron.DOT.ca
Montreal, CANADA

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Marc Champagne <nos### [at] pleasecom> wrote:
> I'm not quite sure if the diamond itself should have a 'collect off'.

  In theory the diamond should collect photons as any other object in
the scene. It's just that photons seldom show any effect on transparent
objects and so it's an optimization to turn photon collection off for
the transparent object (less memory usage and faster rendering).
  There are, however, cases where photons *do* show some effect in the
refracting object itself (for example when it's only partially transparent).
You'll have to test which looks better.

  'collect off' does not affect reflection and refraction of light. It just
tells that photons should not be stored at the surface of the object for
lighting calculation.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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Warp <war### [at] tagpovrayorg> wrote in news:3d8c7816@news.povray.org:

> There are, however, cases where photons *do* show some effect in the
> refracting object itself (for example when it's only partially
> transparent). You'll have to test which looks better. 

...in the refracting object or on the refracting object?

> 'collect off' does not affect reflection and refraction of light. It
> just tells that photons should not be stored at the surface of the
> object for lighting calculation.

and therefore will not affect dispersion either, right?

I better understand 'collect off' now, thanks

-- 
(MIKA) Marc Champagne
marcch.AT.videotron.DOT.ca
Montreal, CANADA

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