black spot in MR


why do I see this black spots on my glass. I have render with MR and use dielectic node.



Hard to tell from the small image, but I think a part of your scene is black from some angle - maybe above/behind the camera is black? Refraction shows things from all angles.



You may need to crank up the photon count, I always get some nasty black splotches when the photon count is too low. Anywhere between 30 to 50 thousand (both GI and Caus) seems to work fine for me. You can also play around with the accuracy and photon width. I’m just guessing it’s the photons.


thanks “imanobody” I will try that.

I look for a way to fix this but not to expand rendering time if that is possible:)


Photons won’t really increase your render times that much, you can pump out tons of photons and render times will only slightly increase. I have a scene that has over 300,000 photons emitted and it only increased the render times by a few seconds (from when it was 30,000 photons). I’m not too sure about causetics, because I don’t really mess with them, but GI’s are really fast. It appears that the time is only increased on the photon emission, not the actual rendering. Of coarse when you turn on FG the render times will skyrocket, but FG is pretty useless for animations and I don’t even use it anymore.

Increasing the Photon Accuracy (Render Globals) will also smooth them out, you may have to go as high as 900. It’s best to set the Photon Radius to the width of the scene in the camera’s frame.


imanobody thanks this good information!!!It realy helps!!!


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