Dust is a problem with all digital single-lens reflex cameras. It can enter the camera whenever you change the lens. This dust often finds its way to the glass filter that covers the digital sensor.
The sensor is made up of millions of light-sensitive elements, each around 6 to 8μm square. It does not need a very large piece of dust or dirt to cover one or more of these elements, or pixels. If a pixel is obscured, it does not receive much light and so that portion of the image will record as grey. These grey areas are most noticeable in light-toned areas of the photograph.
Reducing the problem
Surprisingly, research has shown that one of the main causes of dust is the camera itself. This explains why photographers who rarely change lenses still suffer dust problems.
There are two significant camera-related areas that generate dust. One is the shutter. Every time it fires, friction between the components can create dust. Recent shutter units for cameras have been designed to generate a minimal amount of dust during their operation.
The other main problem area is the plastic body cap. Every time it is attached or removed, friction between the metal mount and the plastic cap can generate dust. Since the first half of 2005, the body cap has been made of a material that produces very little dust from friction.
Prevention is better than cure
You cannot stop dust getting into your digital camera, but you can reduce the risk a little using one or more of these simple procedures.
Switch the camera off before changing the lens. This reduces the static charge on the sensor and stops it attracting dust.
Never leave the camera with the lens mount open. When you remove a lens, replace it immediately with another or attach the camera body cap.
Avoid changing lenses in dusty situations. If you have to change a lens in these conditions, hold the camera with the lens mount facing down to reduce the risk of dust falling into the opening.
Keep the body cap free from dust. Did you know that the body cap and lens cap attach to each other? This will keep the inside of both caps clean when a lens is on the camera.