Camera manufacturers generally advise against any attempt to clean the sensor of a digital camera. It is the manufacturers and suppliers of the specialized cleaning equipment who advocate the process. This is perhaps the best background against which to decide whether or not one should attempt to remove annoying dust particles from the extremely delicate surface of a sensor. Those who choose to ignore manufacturers' instructions and undertake do-it-yourself cleaning should at least proceed with caution and follow carefully the instructions provided by the manufacturer of the cleaning equipment.
The particles which cause problems on sensors are typically too small to be detected by the naked eye. However, it is easy to see whether cleaning is required. Simply take a photograph of a uniform bright surface, or a clear blue sky, using a small aperture such as f/16 or f/22. Then view the image on a computer screen after performing a levels adjustment to see any contamination as black dots. Some of the particles are common airborne dust particles but others may be microscopic shavings of brass removed from the lens mount every time a lens in changed. These settle in to the bottom of the camera and eventually find their way on to the sensor.
Cleaning the sensor of an SLR type digital camera is possible only because the lens can be removed and the shutter held open. Make sure that the instructions for keeping the shutter in the open position are understood before beginning any cleaning process. If the shutter should attempt to close during the cleaning process, significant damage may result. It is also important to ensure that additional contamination is not caused by particles falling from clothing or equipment on to the exposed sensor during the cleaning process.
Some photographers attempt to clean the sensors in their digital cameras using a rubber blower to dislodge dust particles. The camera is held upside down so that dislodged contamination falls free of the camera body. However, this system is unreliable because powerful air blasts may cause damage and an unfiltered blower may deliver additional contamination in to the camera and on to the sensor. Even some of the dust particles dislodged from the sensor may remain inside the camera body and ultimately find their way back onto its surface.
A typical sensor cleaning kit contains clinically sealed swabs of the correct size for a particular sensor, and an appropriate cleaning fluid pack. Prepare an area for the cleaning to be undertaken and make sure it is as clean and dust free as possible. Remove the lens from the camera and lock the shutter open. Cut the end from the swab pack at the handle end and carefully remove the clean swab. Some swabs are preloaded with the correct amount of cleaning fluid, but others must be moistened in an appropriate manner. In the latter case, apply the recommended quantity of cleaning fluid to the end of the swab and, starting at one end, very gently wipe the swab across the length of the sensor. Then reverse the swab and repeat the process in the opposite direction. Note that each side of a swab should be used only once. Discard the swab, close the shutter and refit the lens. Another photograph of a uniform bright surface should now be taken and examined to check that contamination has been removed.
Another type of swab uses a dry adhesive to collect contamination from a sensor. The swabs are just placed on the sensor and then removed, as opposed to being swept across its delicate surface. The manufacturers claim that no deposit is left on the surface of the sensor and that the adhesive causes no damage to the surface of the sensor.
Other cleaning systems use a small vacuum cleaner to gently suck contaminating particles from the surface of a sensor. In many cases this contact-free process is sufficient to achieve adequate cleanliness. However, a second wet-sweeper stage similar to the swab system described above can be used to treat persistent problems such as particles which have welded themselves on to the sensor surface. A final dry-sweeper stage is then used to remove loosened particles.
Brushes for cleaning sensors are available in a very convenient form. The brush is charged with the opposite polarity to the sensor and so attracts contaminating particles onto the brush. The brush can be recharged with repeated blasts of air either from a can of compressed air or by working for a few moments with a rubber blower. A visible dust loupe is also available to allow dust to be seen with the naked eye and hence avoid the need for a small-aperture image to be taken.