The advent of digital cinematography has opened up new creative possibilities for how motion is captured. This article explores the influence of shutter angle along with how it can be used as a creative tool for accomplishing one's artistic goals.
The "shutter angle" is a useful way of describing the shutter speed relative to the frame rate. This term is a conceptual relic of rotary shutters, where a disc with an angled opening would spin and let in light once per revolution to expose each frame. The larger the angle, the slower the shutter speed, all the way up to the limit of 360°, where the shutter speed could become as slow as the frame rate. At the other extreme, the shutter speed can be made arbitrarily fast by decreasing the angle.
Although current cameras don't necessarily control shutter speed in this way, the shutter angle terminology has persisted as a simple and universal way of describing the appearance of motion blur in video. If one wants subjects that are blurred for a greater fraction of their frame to frame displacement, then one would choose a larger shutter angle, and vice versa:
By far the most common setting for cinema has been a shutter angle near 180°, which equates to a shutter speed near 1/48 of a second at 24 fps. Any larger, and motion appears more smeared since the end of blur in one frame extends closer to the start of blur in the next frame. Any smaller, and the motion appears more stuttered and disjointed since the blur gap increases, causing frames to become more like discrete images.
Although the above example is helpful for understanding the underlying behavior, one typically doesn't see motion blur within each frame as they would in a still image. In practice, the shutter angle also has a more subjective influence on the overall feel of motion footage even if one isn't necessarily aware of the precise settings. Click on the examples below to see the difference:
Note how the difference between each shutter angle is barely noticeable at the start of the race (when the action is farthest away), but becomes progressively more apparent as the children's motion becomes closer to the camera. At that time, stills from the above videos depict dramatically different motion blur:
Although many film cameras were capable of only certain shutter angle ranges, digital cameras provide many exciting new possibilities. Just as focal length and aperture have been used as creative tools for controlling sense of scale and depth of field, shutter angle has the potential to do the same for motion.
The optimal setting will ultimately depend on other factors, such as the speed of subject movement within the frame, or the creative intent of the cinematographer. For example, one might wish to use a larger shutter angle to increase the exposure time and reduce image noise in low-light, or to give the impression of softer and more fluid motion. Alternatively, with fast action one might place more importance on depicting crisp details in each frame by using a smaller shutter angle.
Another consideration might be the film era one desires to emulate. Shutter angles much less than 180° more closely mimic the style of old 1950's newsreels, for example, and a shutter angle of 180° will typically give footage a standard cinematic style.