range of cameras. Reliability SLRs vary widely in their construction and typically have bodies made of plastic or magnesium. Most manufacturers do not cite durability specifications, but some report shutter life expectancies for professional models.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 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. Price and affordability The price of SLRs in general also tends to be somewhat higher than that of other types of cameras, owing to their internal complexity. This is compounded by the expense of additional components, such as flashes or lenses. The initial investment in equipment can be prohibitive enough to keep some casual photographers away from SLRs, although the market for used SLRs has become larger particularly as photographers migrate to digital systems. Future The digital single-lens reflex camera has largely replaced the film SLR for its convenience, sales, and popularity at the start of 21st century. These cameras are currently the marketing favorite among advanced amateur and professional photographers. Film-based SLRs are still used by a niche market of enthusiasts and format lovers. See also Asahi Pentax Fujifilm Lenses for SLR and DSLR cameras Scheimpflug principle Zeiss Ikon References Further reading Spira, S. F. The History of Photography as Seen through the Spira Collection. New York: Aperture, 2001. . Antonetto, Marco: "Rectaflex – The Magic Reflex". Nassa Watch Gallery, 2002. External links Photography in Malaysia's Contax History, Part II. 'Innovative Cameras' by Massimo Bertacchi Rolleiflex SL 66 (Rolleiflex SL 66 Medium Format Single Lens Reflex camera). Cameras by type SLR cameras