Almost caustic effect in GI pass with HDRI

[francomanko]

Hi, so im not sure whats going on here but ive just noticed it and it doesnt look right to me. More likely than not im getting confused due to a lack of understanding of vraysun and GI, but I thought i would ask.

Scene is a chrome object in front of flat plane, which is standard vray material..no reflections. Im getting some caustic like effect appearing on the back plane. in the GI pass when i use a dome light and hdri. Its not present at all or really diminished when using vraysun.

Also why is the ground getting loads of GI in the vraysun but virtually none in the hdri version?


Using maya 2022.1
V-Ray 5 for Maya, update 1.2 (v5.10.22, revision 30963 from Sep 1 2021)
2*2080ti with NVLINK
Recommended nvidia drivers.

SCENE LINK

https://drive.google.com/drive/folde...WB?usp=sharing

First image, is rendered with hdri


Second is vray sun

[francomanko]

This is it in context within my scene, with a duplicate object on right with default vraymtl. Pretty sure it didnt use to render like this

[hermit.crab]

The effect is caused by the Reflective Caustics (which are always active when rendering with GPU). Not sure why the VRaySun's effect is so dim. I'll investigate.

[hermit.crab]

The sun is disabled on your scene, by the way, though activating it wouldn't make much of a difference. The difference in caustics is due to the small size of the sun, meaning less chance for rays to create caustics (dome lights are quite spread in comparison). Increasing the sun's radius, glossier shader reflections, or just using regular photon caustics should yield a better caustics effect,.

[francomanko]

ah ok, thanks for info, much appreciated..