Leica’s M mount was introduced in 1953 alongside its first camera, the M3. The bayonet system of the M mount was a drastic improvement over the previous 39mm thread mount Leica used. The M system is faster and has better quality lenses and bodies.
Leica M cameras had large, combined viewfinders with coupled framlines and rangefinders for achieving perfect focus. The cameras were quiet, robust, and reliable, quickly becoming the camera of choice for professionals like Henri Cartier-Bresson.
After the release of the Nikon F, however, SLRs quickly became the dominant camera type. Rangefinders simply could not match the versatility that SLRs offered, with changeable prisms, TTL viewfinders, and access to a wider range of lenses.
Rangefinders were thus relegated to niche uses that their style better suits. Leica M rangefinders excel in street photography and other situations when discretion is key. Both the cameras and the lenses are quiet, small, and discrete.
Leica offered a number of adapters that allow screw mount (LTM) lenses to work properly on M bodies. With the right adapter, even the proper framelines would appear in the viewfinder.
Most Leica M cameras do not require a battery to operate. The M6, M7, and CL are the only exceptions, losing some or all functionality when the batteries are removed. The Leica MP is one of the only 35mm film cameras still available new.
Leica lenses are among the best in the world, and their optical designs have stood the test of time over the past 60 years. They provide excellent contrast, resolution, structure and tonal depth, while retaining a classic character that many pros prefer to the clinical sharpness of Canon or Nikon lenses. Build quality of Leica lenses is exceptional.
Leica M mount has also been used by other camera and lens manufacturers, such as Cosina Voigtländer, Carl Zeiss, Konica, and Minolta.