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I have a bunch of boxes flying apart in Cycles, and I'm using the Vector Blur node for motion blur. Nothing's blurring.

It's the simplest compositor setup: RenderLayer Image/Z/Speed goes to Vector Blur node Image/Z/Speed, Vector Blur node goes to Comp.Out and Viewer.Out. I've tried all sorts of settings on the VB node, but nothing changes. What have I not set up?

Blend file: https://www.dropbox.com/s/8k6n3cr3wu2iwqo/logo_match.blend?dl=0

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  • $\begingroup$ Is it possible you could upload your .blend? $\endgroup$
    – gandalf3 ♦
    Oct 20, 2015 at 21:43
  • $\begingroup$ Trying to remember how (blush)... Done. $\endgroup$
    – OroNZ
    Oct 20, 2015 at 21:46
  • $\begingroup$ @Carlo Be careful when re-uploading .blends. In general it's probably not as important to upload question .blends compared to answers. $\endgroup$
    – gandalf3 ♦
    Oct 20, 2015 at 22:13
  • $\begingroup$ Uh, sorry @gandalf3! I'll carefully read that post. Thanks for the advice. $\endgroup$
    – Carlo
    Oct 20, 2015 at 22:18

1 Answer 1

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This is because the vector pass can't "see" through transparent (glass) objects; in this case all it sees is the lens object, which is remaining motionless relative to the camera.

To render with motion blur in this situation, you'll have to use Cycles' built in motion blur. Enable it in Properties > Render settings > Motion Blur:

enter image description here

And remove the vector blur node in the compositor.

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  • $\begingroup$ Oh you are KIDDING me :( Drat, drat and double drat. OK, I'll re-do the scene and teleport the lens into shot once the vector blur's done its job. DRAT. But thanks :) $\endgroup$
    – OroNZ
    Oct 20, 2015 at 22:35
  • $\begingroup$ @OroborosNZ Any reason you need to use vector blur? Cycles blur should just work™ out of the box $\endgroup$
    – gandalf3 ♦
    Oct 20, 2015 at 23:58
  • $\begingroup$ Cycles Motion Blur does work, and well.... I'm just trying to shave render time, and Vector Blur's faster. I don't have a comp I can dedicate to Sheep-it, and I don't really have much idea around sending files to a render farm. So I'm doing my best to shave seconds, and finding my own line between "noisy output" and "artistically-intended, post-modernistic style" :P $\endgroup$
    – OroNZ
    Oct 21, 2015 at 0:27
  • $\begingroup$ OK, tried the lens teleport approach - but now there's a savage light dip when the lens goes in front of the camera. RAAAGE. Looks like Motion Blur IS my only option, or I'm spending hours/days trying to find out why a perfect virtual lens is also absorbing light =>:-[ $\endgroup$
    – OroNZ
    Oct 21, 2015 at 0:42
  • $\begingroup$ @OroborosNZ The lens's glass shader color is set to .8 white. Setting it to 1 should fix it $\endgroup$
    – gandalf3 ♦
    Oct 21, 2015 at 6:23

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