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A dust reduction system, or dust removal system, is used in several makes of digital cameras to remove dust from the image sensor. Every time lenses are changed, dust may enter the camera body and settle on the image sensor.
Digital single-lens reflex cameras (DSLR) are particularly vulnerable to this issue, since the interior of the camera is exposed during lens changes unlike other forms of digital cameras, and the image sensor is fixed, unlike a film camera. Even the tiniest (micrometre-size) dust particles or other contaminants that settle on the face of the image sensor (individual pixels of which have dimensions on the order of ~5 micrometres) may cast shadows and thus become visible in the final image as more or less diffuse grey blobs, depending on aperture.
Dust may be generated by internal moving parts or may be moved by air currents within the camera. Some systems remove or clean the sensor by vibrating at a very high frequency—between 100 hertz and 50 kilohertz.