sentences:  Most SLR and DSLR cameras provide the option of changing the lens.This enables the use of lens that are best suited for the current photographic need, and allows the attachment of specialized lenses.Film SLR cameras have existed since the late 1950s, and over the years a very large number of different lenses have been produced, both by camera manufacturers (who typically only make lenses intended for their own camera bodies) and by third-party optics companies who may make lenses for several different camera lines.