Black Blotches in Refraction

[stefan.deak]

Ok, so you can see in the image I get some weird artefacts on the right and left side of the rendering. I cannot figure out what is causing them and how to fix them. Does anybody have any idea?

other details:
The glass has a bit of thickness and Im using a basic glass material: black diffuse, reflection refraction set to 1, both IORs at 1.52, thin disabled

The blotches show up in the refraction element. If I use thin glass or hide the glass, they disappear. They also disappear if I hide the wood ribs but keep the glass as it is now.

All lights have generate caustics disabled and caustics in performance tab are disabled. Both the glass and the rib meshes are clean - quads only, no overlapping faces or anything like that. no smoothing and normals are fine.
Also, theres no displacement, just bump and normal maps on all materials except one which is irrelevant for this shot. Its just some towel material somewhere in a corner.

Corona ver is 5

[GeorgeK]

Do you get the same effect if you disable the glass reflection (or lower significantly), also do you by any chance use any reflection/refraction overrides?

On a short test I did I couldn't recreate the problem even with wood textures, but it's highly likely I am missing something. Lastly, are you getting the same black shadow artifacts if the diffuse is disabled on the ribs?

[stefan.deak]

Thank you for your help!

So lowering or disabling the glass reflection doesnt change anything.
There are no overrides, just a good ol CoronaSky in the 3dsmax env slot.

And yes! disabling the diffuse on the ribs, the shadows disappear. If I unplug the map, or plug in a different map, or if I use material override, excluding the glass, nothing changes. Just changing the diffuse to 0 mmakes a difference.

[romullus]

Can you try to use rayswitcher material on the glass object? Thin glass in GI slot and normal (refractive) glass in other slots.

[stefan.deak]

Hello romullus,

I tried it. It didnt work. :(

UPDATE - actually, using thin glass in direct override and normal refractive glass in all the other slots, fixes the problem

[stefan.deak]

I actually recreated the problem with just boxes and pretty much default settings and default materials. I attached it and its rendering.
Im sure Im just missing something super obvious and basic...

[GeorgeK]

I actually recreated the problem with just boxes and pretty much default settings and default materials. I attached it and its rendering.
Im sure Im just missing something super obvious and basic...

Your issue seems to be related with UHD precision, and being very obvious in your current scene setup, try the following:

• Set your UHD precision to 8.0+, or set Animation (flicker-free)
• Set your secondary solver as Pathtracing, it will impact your render times

Lastly you can do as Romullus suggested!

[stefan.deak]

Nice! Thank you! I tried everything you said and all of your solutions solve the problem in my big scene as well.

Thanks again!