Flange focal distance

For an interchangeable lens camera, the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), back focus[1] or register, depending on the usage and source) of a lens mount system is the distance from the mounting flange (the interlocking metal rings on the camera and the rear of the lens) to the film or image sensor plane. This value is different for different camera systems. The range of this distance, which will render an image clearly in focus within all focal lengths, is usually measured to a precision of hundredths of millimetres, and is not to be confused with depth of field.

Not to be confused with front focal distance.
Image of Flange focal Length (2 types camera)
Diagram illustrating the flange focal length of an SLR–type and a mirrorless–type camera

Lenses can be adapted from one mount (and respective FFD) to another. FFD determines whether infinity focus can be accomplished with a simple non-optical adapter. Optics to correct for distance introduce more cost and can lower image quality, so non-optical lens adapters are preferred. A simple non-optical adapter holds the longer FFD lens the appropriate additional distance away from the sensor or film on the shorter FFD camera. A camera body with a shorter FFD can accept a larger number of lenses (those with a longer FFD) by using a simple adapter. A lens with a longer FFD can be more readily adapted to a larger number of camera bodies (those with a shorter FFD). If the difference is small, other factors such as the sizes and positions of the mounting flanges will influence whether a lens can be adapted without optics.

Standard mounts

Typically, camera bodies with shorter flange focal distance can be adapted more readily to lenses with longer flange focal distance.

Mount Flange
focal distance		 Type Format Production Prime lenses Zoom lenses Wide/tele converters Mount converters Comments
Samsung NX mini6.95 mmMirrorless1"2014-201521
Pentax Q-mount9.2 mm[2]Mirrorless1/2.3" (6.17×4.55 mm) / 1/1.7"2011–20195301
M58×0.75 mm mount12 mmIndustrial24×36 mmIndustrial area and line scan cameras
D-mount12.29 mmcine8 mm(8 mm movie cameras)
CS-mount12.526 mm[3][4][5]TV1/4", 1/3", 1/2"(surveillance cameras)
Nikon Z-mount16 mmMirrorless24×36 mm2018–19111
APS-C (DX)2018–142Can use any of the 24x36 mm lenses and the FTZ/FTZ II mount adaptor.
DJI DL-mount16.84[6]MirrorlessSuper 352017–40
Nikon 1-mount17.00 mm[7]MirrorlessCX2011–2018381
C-mount17.526 mm[8]cine / TV8 mm, 16 mm, 1/3", 1/2", 2/3", 1", 4/3"~1926–(Bolex, Eclair and Bell & Howell)
Fujifilm X-mount17.7 mmMirrorlessAPS-C2012–121121[9]
Canon EF-M-mount18.00 mmMirrorlessAPS-C2012–3501
Sony E-mount18.00 mmMirrorlessAPS-C2010–61442

Lens count doesn't include 3rd party products. All FE lenses (see below) can also be used on APS-C E-mount cameras.

24×36 mm (FE)2013–221743

Lens count doesn't include 3rd party products.

Sony FZ-mount19.00 mmcineSuper 352011–0203
24×36 mm2015–12
Micro Four Thirds System19.25 mmMirrorless4/3"2008–372811
Hasselblad XCD mount18.14 mm (+0.05/-0.00)MirrorlessMedium Format (127) 43.8×32.9 mm2017–1313for Hasselblad X System
Canon RF mount20.00 mmMirrorless24×36 mm2018–12113
Leica L-Mount (formerly CL-mount)20.00 mmMirrorless24×36 mm, APS-C2014–33
JVC 1/3" bayonet mount25.00 mmTV1/3" 3-CCD (5.24×2.94 mm)
Samsung NX-mount25.50 mmMirrorlessAPS-C2010–201588
Fujifilm G-mount26.7 mmMirrorlessMedium Format (127) 43.8×32.9 mm2017–72 1for Fujifilm GFX series cameras
Pentax Auto 11027.00 mmSLR13×17 mm1978–19855100
RED ONE interchangeable mount27.30 mmcine
Leica M-mount27.80 mm[9]Mirrorless24×36 mm1954–aka Voigtländer VM-mount, Epson EM-mount, Zeiss ZM-mount as well as Konica KM-mount (Hexar RF) and Minolta M-mount (CL/CLE)
Nikonos28.00 mm[10]underwater24x36 mm1963-20016000this is the underwater scale focusing camera
M39×26tpi mount28.80 mmMirrorless24×36 mmLeica M39×26tpi aka LTM (Leica Thread Mount) aka L39 (not to be confused with M39×1)
M39×1/28.8 mount28.80 mm[11]Mirrorless24×36 mm1948-1978Zorki M39×1/28.8 for Zorki cameras (not to be confused with M39×1 and M39x26tpi)
Contax G-mount29.00 mmMirrorless24×36 mm1994–20056101
Olympus PEN F (film)28.95 mmSLR18×24 mm1963–1972162
Hasselblad XPan34.27 mmMirrorless24×36 mm & 24×65mm1998–20033000Identical to Fujifilm TX series cameras and mount
Contax RF-mount34.85 mmMirrorless24×36 mm
Nikon S-mount34.85 mmMirrorless24×36 mm1947–2005
1/2" TV bayonet mount35.74 mmTV1/2" 3-CCDJVC, Hitachi, Panasonic, others, but not Sony
Minolta V-mount36.00 mmSLRAPS-H1996–19993501Vectis S-1, Vectis S-100, Dimâge RD 3000
Sony 1/2" TV bayonet mount38.00 mmTV1/2" 3-CCD
Olympus Four Thirds System38.67 mmSLR4/3"2003–201712302
Aaton mount40.00 mmcine16mm/S16
Panavision SP70-mount38.00 mmcine2018–35 mm & 65mm
Konica F-mount40.50 mmSLR24×36 mm1960–196517000
Konica AR-mount40.50 mmSLR24×36 mm1965–1988361610
Canon FL-mount42.00 mmSLR24×36 mm1964–1971
Canon FD-mount42.00 mmSLR24×36 mm1971–199010734
Start (Soviet SLR)42.00 mmSLR1958–1964
Minolta SR-mount43.50 mmSLR24×36 mm1958–20016
Fujica X-mount43.50 mmSLR24×36 mm1980–1985
Pentaflex (16 mm cameras)44.00 mmcine
Canon EF-mount44.00 mmSLR24×36 mm / APS-H / APS-C1987–4764
Canon EF-S-mount44.00 mmSLRAPS-C2003–2900
Praktica B-mount44.40 mmSLR24×36 mm1978–1990
Sigma SA-mount44.00 mmSLR24×36 mm / APS-C1992–141924
Arri LPL 44.00 mm cine 25.54x36.70 mm 2018- for Arri Alexa LF
Minolta/Konica Minolta/Sony A-mount44.50 mmSLR24×36 mm1985–42+0+1750+2+136+0+22+0+0
APS-C2004–0+0+30+3+130+0+00+0+0
Rollei QBM44.50 mm[12]SLR24×36 mm1970–Rollei, Voigtländer
Samsung Kenox mount44.50 mmSLR24×36 mm1997–200212 (3?)00Although designed in 1990s, mount is manual-focus only; lenses mount and lock on a slightly modified Minolta A-mount adapters
Exakta44.7 mm[13]SLR24×36 mm1936–1969
M39x145.20 mm[14]SLR24×36 mm1952–1968Early Russian SLRs (Zenit) (not to be confused with M39×26tpi and M39×1/28,8)
M37×145.46 mmSLR24×36 mm1952-1957Asahiflex I, Asahiflex IA (Tower 23), Asahiflex IIB (Tower 23/24), Asahiflex IIA (Tower 22)
M42×145.46 mmSLR24×36 mm1949–Pentacon, Pentax, Contax S, Praktica, Zeiss ZS, Zenit, many others (not to be confused with T-mount, which is M42×0.75)
Pentax K-mount45.46 mmSLR / Mirrorless24×36 mm / APS-C1975–147[15]10883Used also by some Samsung, Ricoh, Chinon, Agfa, Vivitar, Petri and KMZ (Zenit) cameras. Lens count only for Pentax-branded lenses.
Contax C/Y-mount45.50 mmSLR24×36 mm1974–20052453Used by some Contax and Yashica SLR cameras
Petri Bayonet45.50 mmSLR24×36 mmPetri SLRs 1960-77.
Mamiya Z45.50 mmSLR24×36 mm1980–
Kodak Retina DKL-mount45.7 mmSLR / Mirrorless24×36 mm / 28×28 mm1958–197712+6000DKL variants used by Retina Reflex S (034), Retina Reflex III (041), Retina Reflex IV (051, 051/N), Instamatic Reflex (062), Retina IIIS
Voigtländer Bessamatic DKL-mount45.7 mmSLR24×36 mm1958–196711+2100DKL variants used by Bessamatic, Bessamatic deLuxe, Bessamatic m, Bessamatic CS, Ultramatic, Ultramatic CS
Braun Paxette Reflex DKL-mount45.7 mmSLR / Mirrorless24×36 mmDKL variant used by Paxette Reflex Automatic, Paxette Reflex Automatic II, Tower 33 Reflex, Tower 34 Reflex; Balda Baldamatic III; Witt Iloca Electric / Graflex Graphic 35 Electric; Wirgin Edixa Electronica / Revue Edixa Electronica
Voigtländer Vitessa T DKL-mount45.7 mmMirrorless24×36 mm4+?000DKL variant used by Voigtländer Vitessa T; Braun Colorette (Super) II, Colorette (Super) IIB, Colorette (Super) IIL, Colorette (Super) IIBL; Wittnauer Continental, Wittnauer Professional
Yashica MA-mount45.80 mmSLR24×36 mm1(measured); 230AF etc.
Olympus OM-mount46.00 mmSLR24×36 mm1972–20023814
Nikon F-mount46.50 mmSLR24×36 mm / APS-C1959–213117Used by some Kiev F-mount cameras. Only Nikon manufactured lenses counted. Nikon claims that there is over 400 Nikkor lens models manufactured.[16]
Leica R-mount47.00 mmSLR24×36 mm1964–2009
KMZ Zenit DKL-mount47.58 mmSLR24×36 mm1964–19685100Zenit/Зенит 4/5/6 "Байонет Ц", an unofficial DKL-mount variant
B4-mount48.00 mmTV2/3" 3-CCD (9.6×5.4 mm)1992–Mount was in use since at least 1978, wasn't officially standardized until 1992.
Contax N48.00 mmSLR24×36 mm2000–20054501
Tamron Adaptall/Adaptall-250.7 mmSLR24×36 mm1973-20061429326No camera uses Adaptall lenses natively, intended to be used with mount adapters. Many lenses have revisions, only original optical formulas are counted.
Arri STD52.00 mmcine
Arri B52.00 mmcine
Arri PL52.00 mmcine
Leica S-mount53.00 mmSLR45×30 mm1996–
Mini T-mount55.00 mmSLR24×36 mm1957–1962Taisei, M37×0.75
T-mount55.00 mmSLR24×36 mm1962–Tamron T-400, M42×0.75 (not to be confused with M42×1)
YS mount55.00 mmSLR24×36 mm–1969Sigma, Upsilon, Accura, Polaris, Sun, Aetna, Beroflex, Petri, Raynox, N.P.S., Formula, Dionar, Universal, Soligor, Yashica, Spiratone. M42×0.75 (not to be confused with M42×1) Same as T-mount but with aperture coupling
Mamiya 656.20 mmMirrorless6×6 cm1989–19953000Rangefinder camera system, flange focal distance might not be precise.[17]
Panavision PV-mount57.15 mmcine1972–35 mm & 16mm
Mamiya 759.00 mmMirrorless6×7 cm1995–20146000Rangefinder camera system
OCT-1961.00 mmcine
Hasselblad H-mount61.63 mmSLR6×4.5 cm2002–for Hasselblad H System
Mamiya 64563.30 mmSLR6×4.5 cm1975–
Novoflex A-mount63.3 mmSLR(measured) "A"-type adapters for follow-focus system
Contax 64564.00 mmSLR6×4.5 cm1999–
Zenza Bronica ETR69.00 mmSLR6×4.5 cm1976–2004172
Pentax 64570.87 mmSLR6×4.5 cm1984–25822
Rollei SLX74.00 mmSLR6×6 cm1976–2005
Pentacon Six74.1 mmSLR6×6 cm1956–1992Used also by Exakta 66 and Kiev 60 series cameras
Hasselblad V-mount74.90 mmSLR6×6 cm1957–2013for Hasselblad V system
Kowa Six/Super 6679.00 mmSLR6×6 cm1968–197490
Hasselblad 1000F & 1600F82.10 mmSLR6×6 cm1948–1957
Salyut/Kiev mount82.10 mmSLR6×6 cm1972–1980Used by Salyut-S/Салют-C, Zenit/Zenith-80, Kiev 88 cameras
Pentax 6×784.95 mm[18] or 85.00 mmSLR6×7 cm1969–19992523
Zenza Bronica SQ85.00 mmSLR6×6 cm1980–200314
Zenza Bronica GS85.00 mmSLR6×7 cm1983–2002902
Zenza Bronica S2A101.70 mmSLR6×6 cm1959–1980
Rollei SL66102.80 mmSLR6×6 cm1966–1992
Mamiya RZ105.00 mmSLR6×7 cm1982–
Mamiya RB112.00 mmSLR6×7 cm1970–

Precision

Flange focal distance is one of the most important variables in a system camera, as lens seating errors of as little as 0.01 mm will manifest themselves critically on the imaging plane and focus will not match the lens marks. Professional movie cameras are rigorously tested by rental houses regularly to ensure the distance is properly calibrated. Any discrepancies between eye focus and measured focus that manifest them­selves across a range of distances within a single lens may be collimation error with the lens, but if such discrepancies occur across several lenses, it is more likely to be the flange focal distance or the ground glass (or both) that are misset.

Film use

Due to research on optimal flange focal distance settings, it is currently considered better for flange focal distance to be set to somewhere within the film's emulsion layer, rather than on the surface of it. Therefore, the nominal flange focal depth will be equivalent to the distance to the ground glass, whereas the actual flange focal depth to the aperture plate will in fact be ~0.02 mm less.

See also

References
  1. "FOCUS BACK ON BACK FOCUS".
  2. Archived 2012-03-19 at the Wayback Machine pentax.jp
  3. Hornberg, Alexander (2007-02-27). Handbook of Machine Vision. John Wiley & Sons. ISBN 9783527610143.
  4. "CS-Mount | Edmund Optics". www.edmundoptics.com. Retrieved 2018-07-28.
  5. "Flangeback Distances | Universe Optics". Universe Optics. Retrieved 2018-07-28.
  6. "DJI launches Zenmuse X7 Super 35mm camera module with Raw video capture".
  7. "Camera Mounts Sorted by Register".
  8. "C-Mount vs. CS-Mount" (PDF). ikegami.com. Retrieved 4 August 2023.
  9. "Lens accessories | Accessories". FUJIFILM X Series & GFX – Global.
  10. "Nikonos Lenses on Nikon dSLR?". Photo.net Photography Forums.
  11. "The Camera ZORKI Instruction Manual?" (PDF).
  12. Bertram Hönlinger, Carl Zeiss AG (2014): All Zeiss QBM lenses were designed for 44.5 mm. The 44.7 mm value found on some US sites is wrong.
  13. Wrotniak, J. Andrzej
  14. Zenit's mount history: M39x1/45,2
  15. "Zoom Lenses | PentaxForums.com". www.pentaxforums.com.
  16. Nikon F-Mount, nikonusa.com
  17. Ken Rockwell's Mamiya 6 page
  18. Camera Mounts Sorted by Register
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