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Old March 19th, 2009, 10:14 AM   #1
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Time-Warp sequence 720p compatible

My next film has several timewarp sequences (ext. urban, night). Subjective speed should be around 250-300 mph. mimicking high-speed elevated train shooting through a city. It is in 2:35 and with 35mm primes, 24p.

Anyone with relevant experience on this ? Is it better to do all in post (since regular traffic and pedestrians need to be adjusted in SFX anyway) ? If so, what focal length is advisable ?

Or is it better to shoot some of this at low framerates (something like 4 fps) ?

If the latter, is there a way to trick the 250 into this ? (a recent post here deals with slo-mo only) Or should it be done with a still camera (I have a Nikon 200 capable of unliited 4 fps in jpeg S format but buffer-limited in RAW) ?

Thanks !
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Old March 23rd, 2009, 03:49 PM   #2
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Hi Claude,
I like working with motion effects, and can give you some ideas, although I highly encourage testing and experimenting to find the look that you think interprets the feel you are going for, since this is subjective to a degree.

of course any footage can be sped up without frame loss, but the general problem is that motion looks very "stepped". There is no motion blur in the frames as one would have with a real camera observing motion at this rate.

A look I like for many things is shooting at slow shutter speeds at 24p this can be 1/6 sec on our cams. What you get is groups of 4 identical frames with a a blur spanning that 1/6 second. In the timeline, speed up the footage by exactly 400%, and you will get no repeated frames, and continual motion blur between each frame. This will also look effective at higher speeds - eg 800% will give the look of a shutter at twice the frame rate (normal - 180 as I recall). This is the most extreme, but you may be fine with a less extreme effect at an intermediate shutter like 1/12. The important thing to calculate is the number of repeated frames, and to speed up in an exact ratio to eliminate those without interpolation.

Moving to post and interpolated frames, twixtor (a 3rd party plugin in After Effects) is a very powerful tool for motion effects, and can simulate motion blur quite realistically.

Always nicer to get the desired effect in camera of course.
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Old March 23rd, 2009, 04:13 PM   #3
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Claude.

As a frame of reference think back to the speeder chase in Return of the Jedi. The BG plates were shot at 1fps while walking through the forest with a steadicam.

If you are actually on an elevated train going through the city then I think using 1/6th shutter (treating it as 6 frames per second) and then speeding up in post by 400% should give you the same sense of speed and motion blur. Just make sure you're using a 24p sequence and everything should work out fine.

Test it all ahead of time with different shutter speeds.
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Old March 24th, 2009, 04:25 AM   #4
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Sean, Tim
Many many thanks,
will try this out right away with different shutter speeds.
Will also ask the kids to hand over Return of the Jedi

I'll report back
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Old March 25th, 2009, 01:30 PM   #5
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Hey Tim - snap!

I love this look and I've been doing it since I got video cameras with slow shutter speeds. I know I'm not the originator, but it did come to me without prior explanation - I should put up an example if I can make the time...
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