Different reflections in animation

[flat]

The attached scene will rotate once in 30 frames.
The objects are in exactly the same position at frame 0 and frame 30, but the reflections look different.
Lighting is fixed.

What is the cause of the difference in reflection between frame 0 and frame 30?

GI, Max Trans, Adaptive Light Sample is not the cause.
The problem is only seen on V-Ray CPUs, not on V-Ray GPUs.

Confirmed with 3ds Max2021 Build 5.20.02

[caypiranha]

try to switch the mode "stochastic" to "normal" in the Option Rollup on Material´s settings. Also "clip" will produce this wrong effect.

( I really also would like to know why this stochastic is behaving like this
Well yes on one hand - it´s stochastic nature. But what is the advantage of that?)

[^Lele^]

Would you be able to mail me the offending parts of the scene, flat ?

[flat]

try to switch the mode "stochastic" to "normal" in the Option Rollup on Material´s settings. Also "clip" will produce this wrong effect.

caypiranha Thank you for pointing out.
I'm not using Opacity Map, so I didn't expect Opacity mode to affect refraction.
Certainly the problem disappears when Opacity mode is set to "Normal".

This seems like a bug in Stochastic Opacity mode.
If it's a Stochastic mode specification, it shouldn't be the default. >> Chaos developer

[flat]

Would you be able to mail me the offending parts of the scene, flat ?

Hello ^ Lele ^
I have attached a max scene Zip that can confirm the problem to Post#1.

[^Lele^]

Hello ^ Lele ^
I have attached a max scene Zip that can confirm the problem to Post#1.

Uff, thank you, long day.
Sorry for missing it.

[^Lele^]

In the zip attached i don't seem to be able to reproduce the issue: the two look identical at frame 1 and 30.
Is there any trick to getting it to misbehave?

[caypiranha]

In the zip attached I don't seem to be able to reproduce the issue: the two look identical at frames 1 and 30.
Is there any trick to getting it to misbehave?

...may you read also more on post #2 .. and the Trick?...yes - try it again. But better after the long Day with fresh Coffe...! =)

but interesting on your attempt: in my case, I was opening this scene, rendered Frame 1 and frame 30 and I had the mismatch as shown from flat-san directly. Found this issue pretty much reproducible.

I have no idea what the real advantage of the stochastic feature is. More Information about this would be much appreciated!

almost logical, "stochastic" then might tend to flicker somehow during the animation itself - since its nature seems to be a coincidence. Why only the end doesn't match up with the beginning?
In the end, it simply bothers the Artists because of such surprises coming from a feature/options corner, which is in daily life not very frequently used. The hint / last sentence from flat-san in #4 to the Developers are definitely worth taking into account.

[caypiranha]

caypiranha Thank you for pointing out.

Do itashi mashite. your Scene was quite clear and I remembered last Days on where I stumbled over this setting for different reason. Usually no need to me either visiting this rollout. But so then the stochastic word was still in my mind. I just gave it a try. Just luck.

[flat]

In the zip attached i don't seem to be able to reproduce the issue: the two look identical at frame 1 and 30.
Is there any trick to getting it to misbehave?

Here is a screen capture.
https://drive.google.com/file/d/1Yyz...FRPpt_m7l2gxS/

Can't you confirm like this? The difference is subtle.

[kosso_olli]

I can confirm the issue, happening here as well.

[^Lele^]

My bad, indeed.
Issue confirmed and logged.
You're right stochastic opacity should have any influence, this is a bug.

[flat]

Thank you for registering the log in the bug tracker.

[^Lele^]

You're welcome, thank you for the patience.
I can be awfully dense.

[kosso_olli]

Which of the results is the correct one? Frame 1 or 30? Or none of them?