Flange Focal Distances

The distance between the outermost surface of the lens mount and the film/sensor plane is known as the flange focal distance. SLRs typically have longer distances to acommodate the mirror, which results in larger lenses. Rangefinders and mirrorless cameras which do not require a mirror box tend to have smaller lenses and more compact dimensions.

If the focal distance is not accurate, the lens cannot achieve infinity focus (the ability to focus on the furthest object) but will still be able to focus at closer distances. This is the reason some lenses (those with shorter flange focal distance requirements) cannot be adapted to some camera bodies (those with longer flange focal distances).

This table shows popular mounts and their flange focal distances:

Mount	Flange Focal Distance	Year Introduced
Canon EF	44.00 mm	1987
Canon EF-S	44.00 mm	2003
Canon FD	42.00 mm	1971
Canon FL	42.00 mm	1964
Contax/Zeiss M42 Screw (42 x 1mm)	28.8 mm	1949
Contax C/Y	45.50 mm	1975
Contax G	29.00 mm	1994
Fujica X	43.50 mm	1980
Konica AR	40.70 mm	1965
Leica M	27.80 mm	1955
Leica R	47.00 mm	1964
Leica M39 Screw (39 x .977mm)	28.80 mm	1930
Minolta SR	43.50 mm	1958
Minolta/Sony A	44.50 mm	1985
Sony E	18 mm	2010
Nikon F	46.50 mm	1959
Olympus OM	46.00 mm	1972
Olympus Four Thirds	38.67 mm	2003
Olympus/Panasonic Micro Four Thirds	20 mm	2008
Pentax M42 (42 x 1mm)	45.46 mm	1952
Pentax K	45.46 mm	1975
Pentax Q	9.2 mm	2011
Samsung NX	25.50 mm	2010
Sigma SA	44.00 mm	1992
Soviet M39 Screw (39 x 1mm)	45.2	1930
Tamron T2 Screw (42 x .75mm)	55.00 mm	1957