Digital SLR Cleaning for Beginners
Why does the sensor get dirty?
Ten years ago, when most images were shot on film, dust was not much of a problem for photographers. Since a fresh piece of film was used for each exposure, any dust present on the film only affected that single exposure. Of course dust was a big problem for the photo laboratories that developed and printed film. A good lab would go to extraordinary lengths to prevent dust spots spoiling your prints. With today’s digital cameras, every exposure is made on the same imaging sensor. Hence a spot of dust on that sensor will appear on every image.
Because most compact digital cameras have a fixed lens and a well-made case, dust does not often find its way inside the camera and onto the imaging sensor. Although its not unusual for an older compact camera to suffer from the odd spot or two of dust. However a digital single lens reflex camera has a removable lens. Every time the lens is removed, dust is given an opportunity to enter the camera. Once inside the camera, it can (and does) find its way onto the sensor. In addition, some zoom lenses, particularly those with a push-pull action can create air currents within the camera, which stir up any dust present, again allowing some dust to contaminate the sensor.
The particles that end up on the sensor can come from a variety of sources. Most dust generated in the household comes from the occupants, in the form of discarded skin cells. But dust particles also include pollen, diesel particulate as well as material generated by wear and tear inside the camera itself. In windy conditions, larger airborne particles may enter the camera such as sand, which potentially can be very damaging to the sensor.
So we have to conclude that for the DSLR owner, the dust problem has been moved from the photo-laboratory, back to the photographer. Although dust does spoil an image, it is an easily managed problem. The advantages of an interchangeable lens system, in addition to the image quality achievable from the large sensor size far outweigh the inconvenience of a few dust spots that are easily cleaned away.