Op 10-8-2022 om 17:42 schreef Alain Martel:
> The HDR map never emit photons.
> What you can do to get caustics from an HDR map is to use radiosity. As 
> the surface receiving the caustics is close to the objects causing it, 
> your radiosity settings can still be lenient. You only a small 
> error_bound value.
> 
> Try this as a starter :
> 
> global_settings{ assumed_gamma 1
>      radiosity{
>          error_bound 0.1 // may try smaller
>          count 150 1111
>          low_error_factor 0.2
>          pretrace_end 0.005
>          }
>      }

Excellent suggestion, concentrating on the caustics! Thanks Alain. This 
is the result with:

error_bound      0.01
low_error_factor 0.1
pretrace_start  8/max(image_width,image_height)
pretrace_end    1/max(image_width,image_height)

and stochastic render:

+am3 +a0.01 +ac0.90 +r3

render time was only about 10 minutes.
-- 
Thomas

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