Here's an example with the simplest possible node setup:

enter image description here

For some reason, all glossy materials using the Principled BSDF are super rough when viewed in a mirror.

I'm using Blender 2.79. Have I encountered a bug or am I completely missing something else?

I'm using the Cycles Renderer with a GTX 1070.

The blend file is here: https://i.peterwunder.de/mirror_test.blend

  • $\begingroup$ What do you mean by "viewed in a mirror." ? $\endgroup$ Oct 21, 2017 at 20:23
  • $\begingroup$ I have added the information above. I couldn't share the original file since it was well over 400 MB, so I created a new one that exhibits the same problem. $\endgroup$
    – emmalyx
    Oct 21, 2017 at 23:27

1 Answer 1


Too much Glossy Filtering

As said in the manual:

When using a value higher than 0.0, this will blur glossy reflections after blurry bounces, to reduce noise at the cost of accuracy. 1.0 is a good starting value to tweak.

You are using a value of 4.0, that means you are strongly using the filtering for glossy bounces.

enter image description here

Use a lower values to lower the strenght of the blur applied.

That said, actually the principled glossy shader behaves quite differently in comparison with the mere glossy shader in the sensitivity of the filtering.

  • 1
    $\begingroup$ I would never have guessed that this was the culprit. Thank you! $\endgroup$
    – emmalyx
    Oct 22, 2017 at 13:28

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