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I have a scene (attached) where a perfectly diffuse partial sphere gets illuminated by a plane whose texture is set up as an emission BRDF.

My .blend file: https://www.dropbox.com/s/k7w36wlfoewie7p/scene.blend?dl=0

The light plane is so small relative to the light-object distance, that changing the texture has almost zero effect on the rendered images.

The scene is out of my control, and I'm hoping for physically accurate renderings. Is there anything I can do to make the renders responsive to the change of light patterns, even if the light patterns are really far?

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  • $\begingroup$ This may shed some light into why blender.stackexchange.com/questions/65157/… This also seems related blender.stackexchange.com/questions/65243/… $\endgroup$ – Duarte Farrajota Ramos♦ May 1 '19 at 23:49
  • $\begingroup$ @DuarteFarrajotaRamos Thanks! They do seem relevant, but as I said the scene is out of my control, because a physically accurate model of the scene is needed here (so I can't add e.g. a large emission place invisible to the camera). Any ideas? Thansk! $\endgroup$ – Sibbs Gambling May 2 '19 at 13:28
  • $\begingroup$ Not really sure where to look, Cycles might end up being the wrong tool. Maybe you just need an insane amount of samples, or perhaps try changing scene sampling methods (maybe branched path tracing helps), or turning off Multitle Importance Sampling $\endgroup$ – Duarte Farrajota Ramos♦ May 2 '19 at 15:20
  • $\begingroup$ @DuarteFarrajotaRamos Right, I thought about trying branched path tracing too -- will try it now! But as for MIS, why did you suggest turning it off? I thought having it on will help?? $\endgroup$ – Sibbs Gambling May 2 '19 at 15:30
  • $\begingroup$ Not sure if it actually helps or not. I was under the impression it is an optimization to reduce noise at the expense of precision. Maybe turning it off helps, maybe not. $\endgroup$ – Duarte Farrajota Ramos♦ May 2 '19 at 15:49

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