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Tuesday, September 20, 2011

Speed Up To Slow Down

Slo-Mo Video • What You Get Isn’t What You Got • False Magnification?

Labels: ColumnTech Tips

A rafting adventure on the Arkansas River is the perfect subject for slow-motion video. The fastest shutter speed on my Canon DSLR's video mode is 1⁄4000 sec.—plenty fast to stop the action in each frame of the video, which is captured at 60 frames per second, then rendered for viewing in slow motion.

Slo-Mo Video
Q I see videos on TV and YouTube that show the subject in slow motion. Are these photographers using special cameras and software, or can I do this with my DSLR's HD video? I'm especially interested in using this technique for flying birds and wildlife.
J. Crawford
Via the Internet

A I've always been fascinated by slow-motion films that allow us to see what the human eye and brain can't normally discern. So one of the best things about the newer DSLRs with high-definition video is that they offer us mere mortal photographers the opportunity to capture some great slow-motion footage. Here's how to get the best results.

First, it's best to capture the video with the camera set to 60 frames per second (fps) rather than the normal 30 fps. Depending upon your camera, this will probably mean a bit less resolution because, at the higher capture speed, most DSLRs shoot at 720p instead of 1080p. This isn't a big problem because 720p video still looks great on your computer screen or HDTV, but I'm sure that we'll see DSLR video with 1080p at 60 fps soon or maybe even 120 fps at 720p.

Second, set the video function on manual and choose a fast shutter speed for each frame of the video. When the video is slowed down, each frame needs to be sharp. The normal shutter frame rate for video is from 1⁄30 to 1⁄60 sec., but this isn't fast enough to stop action with a fast-moving subject, so every frame would be blurred. Keep in mind also that if the shutter speed is significantly faster than the frame capture rate, the action may not be smoothly portrayed when rendered in slow motion due to the blank time between each capture. Thus, your capture rate and shutter speed are variables you need to consider in the context of the subject's speed of movement and the ambient conditions. To attain faster shutter speeds in the video, the photographer can raise the ISO of the camera and possibly set a larger lens opening.

The third component is the rendering software where the viewing speed can be set for slow motion. I've been using Apple iMovie to render my video, but other programs, such as Adobe Premiere Elements and Apple Final Cut Pro X, have the same capability. If you want to take this to the next level, there are plug-ins for Final Cut Pro X that will smooth transitions in slower renderings.

So the answer is yes; you can produce great slow-motion video with a video-capable DSLR, especially those shooting at 60 fps, and basic video-rendering software. Now all you need is an action subject that lends itself to slo-mo.


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