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Cameras with dust control systems use a variety of mechanisms to repel dust from the sensor (with electromagnetic fields) and to automatically clean the sensor every time you turn the camera on (by vibrating the sensor to "shake off" particles of dust). Every time lenses are changed there is a chance that dust may enter
the camera body and settle on the
image sensor. Even if utmost care is taken when changing lenses, the mechanical parts such as
shutter or quick-return mirror might still generate dust contamination due to friction occurring during their movement. At the same time, these parts create movement of the air inside the camera body which is enough to whirl the minuscule dust particles around.
These problems are not as critical with film SLRs as the dust disappears as the film is wound on, but with DSLRs the image sensor always remains in the same place. Even with dust particles no bigger than 0.1 mm (100 micrometres) and invisible to the human eye, once they land on the image sensor's surface they can degrade the quality of all the images taken thereafter. Furthermore, it is usually a difficult task to remove the dust, often making it necessary to send the camera in for servicing.
Two kinds of dust
There are two main types of dust that can potentially degrade image quality: Dust particles that adhere through electric force and dust particles that adhere through intermolecular force.
(1) Dust particles adhering through electrostatic charges
Most of the contamination to be found on the image sensor surface is caused by dust particles as small as just one micrometre (0.001 mm) adhering to it through electrical charges. The particles themselves carry a positive static electric charge, while the image sensor is negatively charged, which makes them attract each other. The same phenomenon can be observed on the surface of LCD and CRT monitor screens.
(2) Dust particles adhering through intermolecular force
The intermolecular force is weaker than electrostatic charges. However, it still attracts microscopic-sized dust to the image sensor with infinitesimal force. While earthing (grounding) the camera can help reduce the problem of electrostatic dust it does not reduce intermolecular attraction. If, for example, flour were drizzled into the camera, it would still adhere to the surface of earthed metal. This kind of dust is attracted by intermolecular force. Liquid also adheres to the image sensor by intermolecular force and such molecules adhere strongly due to their ability to get closer to the adhesion surface, making it harder for dust reduction systems to remove these type of contaminants completely. In such instances, wiping the optical elements in front of the image sensor with cleaning fluid may be necessary.
History of dust reduction systems
Olympus was the first to include a dust reduction system on a DSLR, featuring their Supersonic Wave Filter (SSWF) dust reduction technology on the Olympus E-1 in 2003. All Olympus DSLRs have included this system, as have Panasonic's and Leica's DSLRs; both companies use Olympus technology.
Before that Sigma was sealing the mirror box of their cameras with a protective filter behind the lens mount, preventing dust from entering the camera body.
Other manufacturers, namely Sony (2006), Canon (2006), Pentax (2006), and Nikon (2007), followed suit with their own dust removal technologies. Each manufacturer uses a somewhat different system.
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