I'm seeing a LOT of noise in a scene that uses the Path Tracing kernel where I have an opaque object nestled up very close behind a transparent specular object. The transparent object is supposed to be a windscreen on an aircraft. It's using an Octane Specular Material with the GGX BRDF model, an IOR of 2.417 (it's supposed to be diamond), a dispersion of 0.1, roughness 1% and film width of 1% with a film IOR of 1.7. The opaque object directly behind the windscreen is a blast shield that in the closed position completely blocks the window. The shield is surfaced with a simple plain white (RGB 248,248,250) Octane Glossy Material for now.
When the render first starts, the windscreen looks like dancing diamond dust was sprayed on its surface as OctaneRender resolves the image.
At first I thought the noise was caused by rays bouncing back and forth between the windscreen and the blast shield, but the windscreen is not double-sided so I don't see how that could be the problem. And yet, as you can see in the image, another part of the windscreen where the blast shield is open only shows noise for a split-second before it mostly clears up.
Noise on the closed windscreen never really quite resolves itself, and the denoiser doesn't quite get rid of what's left; leaving faint multi-colored blobs where the noise used to be. And since the denoiser isn't denoising exactly the same way on every frame, I've got some ugly animated blob artifacts dancing around where the blast screens are closed. I get why the denoiser can't do a perfect job; the camera and the subject are both in motion relative to each other and both are in motion relative to the scene light sources, but this noise is ruining my scene.
On the specular windscreen material I've tried turning off the film width, setting dispersion to 0.0, and setting the windscreen IOR to 1.0, with no effect. I also tried adjusting the ray epsilon higher which did solve the problem, at the expense of my transparent objects no longer being transparent. The only thing that sort of works is setting the noise threshold extremely low (0.01%) and setting the maximum samples very high (8192), but holy hell the render times explode in duration. I've attached my camera and Path Tracing kernel settings below:
Is there anything else I could try that won't be such a hit on image quality and/or rendering time? Thanks...