What Is Shutter Angle?
The "shutter angle" is a useful way of describing the shutter speed relative to the frame rate. The term is a relic of rotary shutters in film-based movie cameras, 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 degrees, 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 digital motion-picture cameras (including HD video DSLRs) 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.
Controlling The Appearance In Your Footage
By far the most common setting for cinema has been a shutter angle near 180 degrees, which equates to a shutter speed near 1/48 of a second at 24 fps. Any larger, and motion appears more smeared or "video-like" 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 one 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. You can see two still frames from motion capture at 45 degrees and 360 degrees, respectively. In these examples, the difference between each shutter angle is barely noticeable at the start of the race (when the action is furthest from the camera), but becomes progressively more apparent as the motion comes closer to the camera. At that point, the screen grabs from the videos show dramatically different motion blur.
Although many film-based cameras were capable of only certain shutter-angle ranges, digital is providing 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 optimum setting ultimately will 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 degrees more closely mimic the style of old 1950s newsreels, for example, and a shutter angle of 180 degrees typically will give footage a standard cinematic style.
Ultimately, how you use shutter angle will depend upon your preferences and the looks you’re trying to make. As many still photographers are migrating to doing at least some motion capture, they’ve been under the impression that the creative control of the shutter speed was for still shooting only. As you can see from this article, nothing could be further from the truth. Not only is the shutter still a creative control, but how you use it can have a profound effect on the overall look of your project.
This article by Sean McHugh was originally published by RED Digital Cinema. Visit www.red.com/learn for more.