Here is a pot full of gold coins. The coins are about to be shoved up and out of the pot by a rainbow that comes up and out from underneath the coins. Everything looks as it should.
But when you render it with motion-blur on, it treats the coins as if they are nearer to the camera than the pot is (without making bigger in view as they would be if they actually were nearer!).
The Z-pass reveals that the coins are being seen by Cycles as nearer than anything else as they are the most black:
Can anyone give me any ideas what is happening here?
If you are using physics on it, weird bugs occur with motion blur in 2.72, if that’s the case save a new version blend-271.blend and try rendering in 2.71.
Agree that motion blur with physics is not really the best right now, but based on what I have read before, seeing it addressed in this release cycle will be unlikely because of the culprit being depsgraph limitations.
In a way, the depsgraph refactor will have to be completed and in Master before Blender is able to pass proper transform information to Cycles, which means it might be some months yet before you can do proper physics simulations with motion blur (but sometime this year).
For reference, the depsgraph is an internal system that governs everything related to object relations in Blender, it’s being refactored because the old system is limited and would otherwise block Blender from getting to the next stage in terms of providing state-of-the-art tools.
