sentences:  There are independent optics companies that make lenses for the various otherwise proprietary mount systems, thus providing alternative sources for lenses that are often of equal quality and/or less expensive than the camera maker's own lenses.Another possibility is the use of adaptors that allow mounting a lens for one system on a camera with a different lens mount.However, the use of an adaptor usually results in reduced functionality, typically requiring the manual setting of aperture and focus, or perhaps not being able to use any aperture other than "wide open".