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Motion Control VFX


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#1 Jeremy M Lundborg

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Posted 02 February 2009 - 09:21 PM

I'm shooting a student spec commercial that involves a runner and some VFX. We want to be able to track with the runner and do some VFX around him. The shot involves multiple passes for plates, but we can't afford a huge motion control rig.

Any suggestions on ways to accomplish valid plates within a reasonable cost?

Thank you.

Jeremy
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#2 Phil Rhodes

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Posted 02 February 2009 - 09:42 PM

Find something that moves in a very repeatable way and strap the camera onto it. I've seen (only somewhat successful) motion control done with lego parts, or with a Jimmy Jib on a track and some careful rigging of ropes and pulleys, but what you can get away with depends heavily on how the shot is designed. If you aren't seeing people's (real) feet in contact with the (composited) ground, or any contact between elements from different passes, you can get away with more. I worked on one TV sports promo where the motion control was a normal set of tracks with a toothed belt add-on, and as far as I could see no attempt to phase the camera - but the shot was a low angle looking up at someone walking, the only requirement being to match parallax on an apparently-distant background, so there was lots of room for error. For comparison, I did video assist on another one which was a Milo, multi passed on the same set with speed ramping and animating light sources and costume and set dressing changes and christ knows what else, which was... um... time-consuming, but enormous fun.

Regardless of the precision with which you can repeat the move, however, unless you are moving extremely slowly, you may discover that your inability to phase lock the camera to the motion leaves unpleasant little trails behind things in the final comp.

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#3 Scott Fritzshall

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Posted 03 February 2009 - 12:23 PM

It depends on what exactly needs to be photographed with multiple passes. In some cases, you may be able to get away with using similar passes, and using projection mapping to "rephotograph" them... What exactly is going on in the shot, and what elements do you need to shoot?
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#4 Jeremy M Lundborg

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Posted 05 February 2009 - 05:20 PM

We will be tracking with the main runner who passes up two other runners in the fore/background. I gather we'll need a clean plate, and respective takes with each runner separately. The two runners will evaporate into water as the main runner passes them.

Of course we'd love to get all the passes the same, but with the kinetic motion it's a struggle without a proper rig. My initial thoughts were echoed above in terms of pullies/ropes but with the physical tracking it needs to be a little more sturdy.

At this point I believe the best way to go, as with any photography, is just throw some math at it. Do our best to regulate the speed of our dolly(atv) and then we can at least have a chance in post once we get a solid take with the runners.
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#5 Phil Rhodes

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Posted 05 February 2009 - 06:25 PM

Shoot the runners against blue on treadmills, don't show their feet. Track them into the backdrop later.

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#6 Andy_Alderslade

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Posted 05 February 2009 - 07:49 PM

There are now small motion control rigs now that work with conventional Moy track and can be programmed to do multiple paths and are frame accurate.

They may still be out of your budget to hire but try checking it out, maybe if you can find a locale supplier they will help you out.

http://www.mo-sys.com/

http://www.kontrolfreax.com/

Best of luck,
Andy
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#7 Phil Rhodes

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Posted 05 February 2009 - 09:58 PM

Apropos of nothing, has anyone else noticed how alarmingly accurate the Google promotional analysis of this page is, and how appropriate the ads it's coming up with?

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