Hi,

  looks like it is solved in my "real-life" example. The example with the boxes
and one non-smooth triangle was made up and showed the signs of over
compensation for the reasons you have mentioned. My actual case contains
smooth_triangles with proper normal definition and adding "hollow" solved this
problem right away and the objects behind transparent ones have the proper
amount of depthcuing by fog on it.
Thanks to all, this was rather illuminating and slightly embarrassing for me. I
should have figured it out myself - it only goes to show that I still don't know
the inner workings of povray that well.

Cheers,

   Lothar


"Kenneth" <kdw### [at] gmailcom> wrote:
> > "Lothar" <les### [at] helixnihgov> wrote:
>
> > >
> > >    adding the keyword hollow definitely changes something. It seems to
> > > over-compensate now. The white fog in the back seems to be greatly enhanced!
> >
> > Kenneth wrote:
> > Comment specular and roughness out and the 'extra' fog effect disappears! Or
> > move the lights to some odd angles relative to the triangle.
> >
>
> I thought I would explain that better, in case the solution didn't seem obvious:
> Your triangle is just a flat shape. Since it isn't a 'smooth' triangle, the
> 'normals' across the surface all point in one direction-- straight out at
> 90-degrees to the surface. The SPECULAR/ROUGHNESS addition just bends light rays
> that reach the surface--based on the normals-- to give it a shiny appearance.
> But your lights (one of them anyway) are aligned really close to that 'normal'
> axis-- and so is the camera. The end result is that the entire flat triangle is
> 'shining' almost uniformly due to the specular addition; that shininess adds to
> the brightness of the fog seen *through* the triangle.

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