"Motive17" <nomail@nomail> wrote:
> Good morning to all,
>
> I'm focusing on a quite strange issue.
>
> I have simply defined this light source:
>
>     light_source {
>                  <0,500,-1000>
>                  color rgb <255, 255, 255>
>                  fade_distance 1
>                  fade_power 0
>                  media_interaction off
>                  media_attenuation off
>                      }
>
> and this object:
>
> cylinder {
>               <0, 0, 1000>,
>               <0, 1000, 1000>,
>               (100)
>               pigment {rgb <0, 0, 0>}
>               finish {
>                      ambient 0
>                      diffuse 1
>                      specular 1
>                      emission 0
>                      roughness 0.005
>                      reflection {
>                                 0.5
>                                 metallic
>                                 }
>
> then, gradually I'm moving the light source until z=-100000, leaving the camera
> fixed:
>
> camera {
>           perspective
>         location <0,500,0>
>         look_at <0,500,1000>
>         rotate <0, 0, 0>
>         up <0,2,0>
>         right <2,0,0>
>         }
>
> The strange issue is relative to the behaviour of the light reflected by the
> cylinder. It seems to increase when I increase the distance between object and
> light source. Why? There is any light attenuation defined.
>
> Anyone have an idea about that?
>
> Thank you
>
> Best regard

Try a parallel light and the effect vanish. If I use a spotlight, the visible
radius increase with the distance to the object. Same for the point
light_source.

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