Render nodes rendering refractions differently

[ben_hamburg]

hi there,

I´m having a weird and very annoying problem:

I have sequence with some refractive and glossy refractive materials.
I just checked the previous version from the end of august and it rendered fine.
But now I had to rerender that sequence and I´m getting flickering in the refractive materials.
From the looks of it, I thought it might have been a problem with the number of maxium refractions/reflections beeing too low, so I upped them and rerendered the sequence.
But the Problem persisted.
So I locally rendered some of the frames that had the problem and...they rendered fine locally.
Its also random which render nodes produce the wrong frames, so I´m completeley clueless as to how this might have happend or how to troubleshoot it.
Any ideas?

[tashko.zashev]

Hi,
Have you made any software changes since the last good render? Max or V-Ray Upgrades ?
Would it be possible to show some rendered frames or send the scene file ?
Could it be a missing texture file used as refraction map ?
I assume that a simple new scene works fine with the same setup and network render?

[ben_hamburg]

I just rechecked and the last version was already rendered in may. So it might actually have happend after our last Vray update. We are now on 3.20.02.

[vlado]

If you have any modifiers on the flickering meshes, it might help to remove them; collapsing to an editable mesh might help as well.

Best regards,
Vlado

[ben_hamburg]

I attached two screenshots demonstrating the issue and prepared a scene for support.
I think we updatet Max from 2015 to 2016 and also vray. after the last good rendering.
The only difference I could make out in the rendersettings was tha override value for reflections/refractions, the old scene file had it actually at a lower value then the new one.

How does the reflection/refraction override value actually work? Does it override the material values completely?
Lets say I set the refraction maximum in the material to 5 and the override value to 20 - does it now correct the material values from 5 to 20 or does that override value simply cap the maximum?

[ben_hamburg]

Ok, after rendering the first couple of frames with the override value at 30 the issue seems to be gone now, I´ll have to wait for a couple more frames though.
Also I´d still like to now about the refraction/reflection override, its the first thing I´m trying to tune when dealing with refractions/glossy refractions, since those scenes are notoriously hard to tune...

[tashko.zashev]

Thank you for the update.
We are going to perform a test and see if we can replicate the issue here.

[ben_hamburg]

hi there,

did you have the time to do your own tests?
Because unfortunately my issues aren´t completely gone.
The dark flickering that looked like the maximum of refractions was reached is gone now, but the flickering glow that looked like wrong caustics is still here.
Less obvious than before, but still too bad to let it slip by...

[svetlozar.draganov]

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