Best explanation for shutter speed in video

Trying to figure out what shutter speed to use when shooting various frame rates for video can be a bit of a mind bender.

I’ve just found a forum post by someone going by the name of InterMurph that explains exactly what to use and why:

When choosing a frame rate in video, you want to balance two extremes:

  1. Shutter is open too long, resulting in blurred motion
  2. Shutter is open too short, resulting in choppy motion

In cinematography, the right balance is generally 1 / (frame rate x 2), rounded to the nearest speed supported by your camera. So for 24 FPS, it would be 1/50th of a second; for 30 FPS it would be 1/60th of a second, and for 60 FPS it would be 1/125th of a second.

If that results in video that is too dark, you can definitely keep your shutter open longer, but you are limited to the frame rate (24 FPS = 1/25th, 30 FPS = 1/30th, and 60 FPS = 1/60th). As stated in 1) above, this will result in more motion blur.

If the ideal setting results in video that is too bright, then you can definitely keep your shutter open for shorter intervals. For example, in 24 FPS video, switching from 1/50th of a second to 1/100th of a second is generally OK, but switching to 1/200th could be trouble, particularly if there is a lot of motion. This is because your shutter is open for a much shorter time, and will miss most of the motion. This results in jumpy video.

Think of it this way: a car is moving 24 feet per second. At a shutter speed of 1/25th of a second, each frame covers 1 foot of motion. At a shutter speed of 1/50th of a second, each frame covers 6 inches of motion, and the next 6 inches are missed. At a shutter speed of 1/200th of a second, each frame covers 1.5 inches of motion, and the remaining 10.5 inches are missed. As you increase the shutter speed, you miss more of the motion, and the video gets jumpier.

There are three ways to deal with the problem of an excessive high shutter speed. When you move the shutter speed back towards the ideal, the exposure must be balanced:

  1. By increasing the aperture (f-stop). Since the Inspire camera has a fix f/2.8 aperture, this isn’t an option.
  2. By decreasing the ISO setting. The Inspire camera will do this automatically. But this strategy only works until the lowest ISO setting is reached, which is quite easily hit on a bright day.
  3. By adding a neutral density (ND) filter to block the light. The Inspire camera comes with an ND filter; I recommend using it on any moderately bright day. But this is not an extremely strong filter, and as Kilrah mentions above, we could use some stronger options.

That said, the “jumpy video” problem is not the only one you mentioned. You also mentioned “rolling shutter”, which is another beast altogether. If it is rolling shutter you suffer from, the only cure is to eliminate motion from your video.

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