Reliability of SLRs

SLRs vary widely in their construction and typically have bodies made of plastic or magnesium. Most manufacturers don't cite durability specifications, but some report shutter life expectancies for professional models. For instance, the Canon EOS 1Ds MkII is rated for 200,000 shutter cycles and the newer Nikon D3 is rated for 300,000 with its exotic carbon fiber/kevlar shutter. Because many SLRs have interchangeable lenses, there is a tendency for dust, sand and dirt to get into the main body of the camera through the mirror box when the lens is removed, thus dirtying or even jamming the mirror movement mechanism or the shutter curtain mechanism itself. In addition, these particles can also jam or otherwise hinder the focusing feature of a lens if they enter into the focusing helicoid. The problem of sensor cleaning has been somewhat reduced in DSLRs as some cameras have a built-in sensor cleaning unit.