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Shooting Sports + Slow Motion (LX100 and GX7)
  • Hi there,

    I'm going to take some video of my brother when he races in the World Cup of Skeleton (where they throw themselves headfirst down an ice chute at up to 140 km/h). I own a Panasonic LX100 and a newly-purchased GX7. I'm planning on using the LX100 for the wider shots and when I want to rely on the detail that the 4k brings. I plan on using the GX7 with my longer u4/3 lenses (like P35-100/2.8) and hope to be able to use the DTC functionality as well.

    I have a few questions about techniques and settings needed to shoot fast moving sport, using 50fps (in the GX7), and potentially getting more slow-motion with something like Twixtor to interpolate frames.

    Normally, I try to follow the 180 degree shutter rule for motion blur, and until now I've only had a camera that shoots 24/25/30 fps so I've kept the shutter speed fixed at 1/50 especially when indoors with 50Hz lighting.

    I would like to try to record some of the bobsled and skeleton starts with the intent of slowing them down in post. The GX7 has 50 fps. If I record in 50 fps, should I be setting the shutter at 1/125 or should I be using something higher for sharper image capture, especially if I intend on using something like twixtor to make it look like even slower motion?

    As far as shooting at 50 fps on the GX7 (28 Mbps), is there any loss in image quality compared to shooting at 25 fps (20 Mbps). Is there any reason why I shouldn't always shoot at 50 fps just in case I want to slow anything down in the future?

    Thank you for advise!

  • 4 Replies sorted by
  • You don't have any visible quality loss when shooting at 50fps with the GX7, at least i didn't notice any and shot a music video with one and made a severe color grading, you should be fine.

  • If you intend to post-process some video shot with a software-slow-motion-filter it's a good idea to use shorter exposure times, if light permits shorter by the maximum factor that you want to slow down the material later. Reason: It is very feasible for slow-motion software filters to add some motion blur where required, but those filters cannot really create "additional sharp details" where the original recording is blurred.

  • Also, you make the job for the software slowmo filter easier (and more likely to work well) if the relevant fast moving objects are shot before a background with little detail - such as snow, sky or a very blurred (because out-of-focus) background. In contrast, if you shoot your brother from a perspective where a crowd of spectators is right behind him, and still in focus, chances are that the software fails in separating the background from the moving foreground object sufficiently.

  • Thank you for all the input. I've done some additional research (I was searching the archives for "sports" rather than the software tools "twixtor, or FCPx optical flow" so previously didn't get many results).

    In summary, the suggestions are:

    • Use the highest framerate you have, ie 720p/60 is better than 1080p/30. My (PAL) GX7 has 1080p/50 so I'll go with that.

    • Use the highest shutter speed you have. Less motion blur will help the software tools do the interpolation better, and motion blur can be added back in post.

    • As Karl said, a simple background is best. I'm not sure how I can best do this as the starts have the sledders oncoming and if I use a shallower depth of field to blur the background, there is less time that the althletes will be in the area of focus. I'm going to try to experiment with this and cars or other quick moving objects.

    • Another tip to get the right amount of motion blur is to calculate the 180 degree shutter speed based on the fps you are shooting at * the factor that you plan on slowing down the shot in post. I guess this means that If I'm shooting 50 fps, and plan on slowing down by 50%, I should set the shutter to around 1/200.

    I will play around with Twixtor (demo), FCPx Optical Flow, and the free GoPro Studio 2.5 with flux (which I've read is Twixtor under the hood).