Distance from lens mount to sensor; defines compatibility across camera systems: Canon RF 20mm, Sony E-Mount 18mm, ARRI PL 52mm.
Technical Details
The flange distance is measured with precision instruments to within hundredths of a millimeter. For Canon RF-Mount, it is 20.0 mm, for Nikon F-Mount 46.5 mm, and for ARRI LPL-Mount 44.0 mm. Deviations exceeding ±0.02 mm lead to focusing errors. Mechanically, the dimension is defined by the depth of the bayonet stop and the position of the sensor within the housing. Electronic contacts additionally transmit lens data for automatic aberration correction.
Adapters allow the use of lenses with a larger flange distance on cameras with a smaller value. Conversely, this is not optically possible without correction lenses, which, however, impair image quality.
History & Development
The concept developed with the first interchangeable-lens cameras in the 1930s. In 1982, ARRI standardized the PL-Mount with a 52.0 mm flange distance for professional film cameras. In 2010, Sony revolutionized the short flange distance of 18.0 mm with the E-Mount, enabling mirrorless cameras. Canon followed in 2018 with the RF-Mount (20.0 mm), and Nikon in 2018 with the Z-Mount (16.0 mm).
The trend towards shorter flange distances results from the elimination of the reflex mirror in mirrorless systems. This allows for more compact housings and better adapter compatibility with older lenses.
Practical Application in Film
Short flange distances allow the use of vintage lenses such as Zeiss Superspeeds or Cooke Panchros on modern digital cameras. For "Dunkirk," Christopher Nolan used old Hasselblad lenses via adapters on ARRI Alexa 65. The Sony FX9 with E-Mount allows the direct use of Canon EF lenses via Metabones adapters without loss of quality.
When changing lenses between different camera systems within a production, DoPs must consider the flange distance to ensure consistent focus marks.
Comparison & Alternatives
Long flange distances (PL-Mount 52.0 mm) offer mechanically more stable connections but require larger, heavier lenses. Short flange distances (Sony E-Mount 18.0 mm) allow for more compact designs and universal adapter compatibility but require more precise manufacturing tolerances.
The ARRI LPL-Mount combines the proven 44.0 mm flange distance with a larger diameter for full-frame coverage. RED developed proprietary mounts with variable flange distance through internal mechanics.