If filming indoors, floodlights are often needed to achieve the required lighting level. Bartlett, 1997a, suggests that one floodlight positioned perpendicular to the plane of performance, and one to each side at around 30˚ to the plane, should provide adequate illumination. Filming outdoors in natural daylight is often preferable to filming under artificial lights, but natural light levels are inevitably less predictable. When filming in direct sunlight, the position of the sun will restrict where the camera can be located.
The background must provide a good contrast with the performer and be as plain and uncluttered as possible. When filming indoors with floodlighting, a dark, non-reflective background is preferred. Video cameras often have a manually adjustable setting for different light sources (e.g. daylight, fluorescent lamps, sodium or mercury lamps) and white balance, which can be used to enhance the color rendition. Standard PAL video cameras have a fixed frame rate of 25 Hz, although this can effectively be doubled, provided the camera uses the interlaced scan method.
Most high-speed cameras have adjustable frame rates. The frame rate used will depend on the frequency content of the movement being analyzed, and the dependent variables being studied. Sampling Theorem (see Chapter 7 for more detail) states that the sampling frequency (frame rate) must be at least double that of the highest frequency present in the activity itself.
Lastly comment
In reality, the frame rate should be much higher than this (Challis et al., 1997) suggest 8–10 times higher). A sufficiently high frame rate will ensure that the instances of maximum and minimum displacement (linear and angular) of a joint or limb, and of other key events in a performance (e.g. heel-strike in running, ball impact in a golf swing) are recorded.
