8 Introduction to Shutter Speed
Some video cameras have the addition of shutter speed settings. These act in a similar way to how the shutter speed works on a stills camera, by reducing the time the film or imaging device is exposed to light. The process that a video camera shutter adopts is quite different from a stills camera, but the result is basically the same. Essentially, instead of a mechanical shutter opening and closing, the video camera’s shutter works by charging/refreshing its imaging device for a given time for each frame of video.
The higher the shutter speed, the more you will have to increase the aperture (or decrease the f-number) to obtain a sufficiently exposed image. This can be used to direct your audience’s attention to a specific subject in frame by defocusing items in the foreground and background. In other words – it creates a shallower Depth of Field.
However, video is a moving image, so shutter speed adjustment can also have an effect on the smoothness of movement from frame to frame and the focus of moving images within the frame. Interlaced video is either 25 frames per second for PAL (Phase Alternating Line, the TV system mainly used in Europe, Asia and Australasia) and 30 frames per second for NTSC (National Television Standards Committee, the TV system mainly used in the USA and Japan). These frames are made up of two interlaced fields, which are perceived as one image to the human brain (through the eye’s ability to momentarily retain an image, known as ‘persistence of vision’). At standard shutter speed, moving objects will have motion blur as they move within the 1/25 or 1/30 second exposure. This motion blur helps our perception of smooth movement from frame to frame.