motion blur weirdness

[johnjoe]

Hi,

I'm having an issue with regards to motion blur.

The basic setup is as follows...

I have a simple piece of hoop shaped geometry rotating 360 degrees around the Y axis over 1 frame.

My motion blur settings are

Duration (frames) 1

Geometry samples 25

The problem is that it renders with a dark line running along the Y axis. This shouldn't be happening and I'm out of ideas why this could be.. Hopefully someone here knows?


Massive thanks.


Joe

hoop_motion_blur_v01.mb.zip

[ivaylo.ivanov]

This dark line is actually normal. Intuitively, the probability for the ring to be at any position is equal if you rotate on 360 deg. However, you render a different thing - the probability to hit the front surface of the ring. It's actually 2 times lower at the dead center, since the ring passes this position only one time. Here is a simple image:



If you don't want this dark line, you must make the probability above also equal at all degrees. This is actually simple - make the material fully transparent (without turning on the "Multily color by opacity"). Here is a scene:
mb.zip