7.9: Frame Rate and Shutter Speed

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Christopher Clemens
Laney College, City College of San Francisco, San Francisco State University, Los Angeles City College via ASCCC Open Educational Resources Initiative (OERI)

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Frame Rate

The Frame Rate in video dictates how many individual frames of still images are captured to produce the illusion of motion. Frame rate is measured in Frames Per Second (fps). The higher the frame rate, the slower motion will appear. The lower the frame rate, the faster things will appear to move. The two common frame rates in video are 24fps (really 23.976 fps) and 30fps (really 29.97). Both frame rates make motion happen at a natural speed, but 24fps will give the video more of a film feel because film is typically shot at 24fps (See figure 7.9.1 below), and video is shot at 30fps. When you want to slow motion down and have it look more natural than slowing a video down in editing software, you can increase the frame rate to 60fps or (on some cameras) 120fps (See figure 7.9.2 below).

Figure \(\PageIndex{1}\): Motion at 24 frames per second
(CC BY-NC 4.0; Sebastian Jimenez via San Francisco State University)

A person walking to a camera shot at 24 frames per second. The speed looks normal. — Figure \(\PageIndex{1}\): Motion at 24 frames per second
(CC BY-NC 4.0; Sebastian Jimenez via San Francisco State University)

A man walking to a camera shot at 120 frames person second. The movement looks very slow. — Figure \(\PageIndex{2}\): Motion at 120 frames per second
(CC BY-NC 4.0; Sebastian Jimenez via San Francisco State University)

Shutter Speed

In film photography cameras, there is a shutter inside the body that ensures film is not exposed to light before you hit the shutter release button. When you capture an image by hitting the shutter release, the shutter opens to expose the film to light, thus capturing the image in front of it. The same is true of DSLR cameras, except film has been replaced with an image sensor that is sensitive to light.

Video also has a shutter function, but instead of being a physical shutter that opens and closes many times per second, it is a digital replication of a shutter. The speed at which the shutter opens and closes controls motion blur, the blur we see when an object is moving in a video image if we were to stop on a single frame. The lower the shutter speed, the more light is let in and motion blur becomes more prominent in the video. The higher the shutter speed, the less light is let in and motion blur disappears. It may seem like having less motion blur is ideal, but high shutter speeds make motion look jumpy because each frame has stopped motion. If you wave your hand in front of your face, you’ll notice that the quick motion does not appear crisp and clear, which is why motion blur is natural in video.

The video below will provide examples of the effects of Shutter Speed on recorded movement as discussed above.

To watch this video with closed captions: https://amara.org/en/videos/2ArGEGfc...or-dslr-video/.

180 Degree Rule for Shutter Speed & Frame Rate

The 180 Degree Rule says that if you want your video to look natural, then your shutter speed should be set to double your frame rate. This means that if you are shooting video at 24fps, then your shutter speed should be double that at 1/48 (of a second), but most cameras do not have a 1/48 setting, but 1/50 will do just fine because it is close enough. When you are shooting at 30fps, then you’ll need the shutter speed to be 1/60. The same remains true when you are shooting at 60fps and need a shutter speed of 1/120, and shooting at 120 fps and need a shutter speed of 1/240.