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Odd Framerate Mystery with GH2: No problems, just don't understand something.
  • I did a video shoot recently, and we decided to shoot it at 29.97 fps. So, I set my GH2 to use the high bitrate setting, and set my exposure and manual focus, and we did a few takes.

    Then I noticed that I'd made a mistake: I'd set my shutter speed to 25, i.e., 1/25th of a second. I was concerned that the stuff we'd shot would be unusable, with strange blurs or occasional frame skipping or pull-down, but it looked just fine. (I've shot at 2 frames per second, and that tends to duplicate a lot of frames.)

    As I said, there's no problems I need to fix here, but if someone could explain to me why this setting didn't screw up my video, I'd appreciate it.

  • 6 Replies sorted by
  • You just have longer motion blur. If you don't have any fast motion, or flickering lights, there is nothing to worry about.

  • Hm. I'll look at it more carefully, but it seems that this might be a neat way of getting a film-like look at video framerates. Interesting.

  • I don't know, film like look and motion blur is traditionally associated with 180 degrees shutter, you have 75 degrees shutter here, but, those thinghs have to do with your film being "cinematic" as much as the fact that I haven't had breakfast this morning.

  • When the exposure time is set longer than the frame period, it reduces the effective frame rate. In 30 fps mode with a 1/25 shutter, the effective frame rate becomes 14.985 fps. The video will be recorded with every other frame as a duplicate of the previous frame. Of course 15 fps is low and the shutter speed is slow, but how noticeable that is depends on how much motion there is in what you're shooting. If you have the camera on a tripod doing a wide shot of distant subjects, the low frame rate and slow shutter speed would be difficult to detect in the footage.

  • @Brian_Siano I think some people like to use a shutter speed of 1/40 or 1/30 in order to smooth out and remove "judder" type of look. Some consider that a more film-like look. I guess that's one reason why using 29.97 fps is preferred by some in place of 24 fps...because there is less judder. On the other hand, many people talk about liking 24 fps at 1/50 shutter speed becuase they like the "judder" and say that is more film like.

    I guess the downside to 1/30 is the risk of excessive motion blur, and requires careful slow panning. I've also heard that there are some issues with doing slow motion with 1/30 footage, but I'd research if that's important to you.

    I remember @vicharris had discussed shooting with 1/30 and 1/40, so maybe he can chime in here with his experience and any useful tips.

    One additional nice benefit of 1/30 over 1/50 is that you get 2/3 of a stop more of light which can help on low light scenes.

  • Yep, still never shoot over 1/40 but it's just my preference. I've never had a problem with the stuttering that everyone else has. I love 1/30 when the camera is still or I do slow, controlled cam movements timed with the actors.