Flange 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

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), or register, depending on the usage and source) of a lens mount system is the distance from the mounting flange (the metal ring on the camera and the rear of the lens) to the film 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 in hundredths of millimeters and is known as the depth of focus (not to be confused with the similarly named depth of field).

This distance influences whether a lens from one system can be mounted with an adaptor to a camera body of another system. In order to produce an adaptor that permits focus to infinity without corrective optics, the flange-to-film distance the lens is designed for must be greater than that of the camera body it is to be adapted to, giving room for the adaptor. Camera systems with a large flange-to-film distance have lenses that can be widely adapted, while those with a small flange-to-film distance can take adaptors for many types of lenses.

If the difference is small, other factors, such as the diameters of the mounting flanges of the two systems, come into play as well. Lens adapters are generally easier to make when the camera body has a large lens mount.

Standard mounts include:

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[1]Mirrorless1/2.3" (6.17×4.55 mm) / 1/1.7"2011–5301
D-mount12.29 mmcine8 mm(8 mm movie cameras)
CS-mount12.526 mm[2][3][4]TV1/4", 1/3", 1/2"(surveillance cameras)
Nikon Z-mount16 mmMirrorless24×36 mm2018–211
DJI DL-mount16.84[5]MirrorlessSuper 352017–40
Nikon 1-mount17 mm[6]MirrorlessCX2011–1
C-mount17.526 mm[7]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[8]
Canon EF-M-mount18 mmMirrorlessAPS-C2012–2501
Sony E-mount18 mmMirrorlessAPS-C2010–61142
24×36 mm (FE)2013–111342
Sony FZ-mount19 mmcineSuper 352011–0203
24×36 mm2015–12
Micro Four Thirds System19.25 mmMirrorless4/3"2008–372811
Hasselblad XCD mount20 mmMirrorlessMedium Format (127) 43.8×32.9 mm2017–81for Hasselblad#XCD-System
Canon RF mount20 mmMirrorless24×36 mm2018–223
Leica L-Mount (formerly CL-mount)20 mmMirrorlessAPS-C2014–33
1/3" bayonet mount25 mmTV1/3" 3-CCD (5.24×2.94 mm)JVC
Samsung NX-mount25.50 mmMirrorlessAPS-C2010–201588
Fujifilm G mount26.7 mmMirrorlessMedium Format (127) 43.8×32.9 mm2017–51for Fujifilm GFX 50S
Pentax Auto 11027 mmSLR13×17 mm1978–19855100
RED ONE interchangeable mount27.30 mmcine
Leica M-mount27.80 mm[8]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 mm[9]underwater24x36 mm1963-20016000this is the underwater scale focusing camera
M39×26tpi mount28.80 mmMirrorless24×36 mmLeica M39×26tpi aka L39 (not to be confused with M39×1)
Contax G-mount29.00 mmMirrorless24×36 mm1994–20056101
Olympus PEN F (film)28.95 mmSLR18×24 mm1963–1972162
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 mmTV1/2" 3-CCD
Olympus Four Thirds System38.67 mmSLR4/3"2003–201712302
Aaton mount 40 mm cine 16mm/S16
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 mm
Pentaflex (16 mm cameras)44 mmcine
Canon EF-mount44.00 mmSLR24×36 mm / APS-H / APS-C1987–4764
Canon EF-S-mount44.00 mmSLRAPS-C2003–2900
Praktica B-mount44.00 mmSLR24×36 mm
Sigma SA-mount44.00 mmSLR24×36 mm / APS-C1992–0
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
QBM44.5 mm[10]SLR24×36 mmRollei, Voigtländer
Exakta44.7 mm[11]SLR24×36 mm1936–1969
M39x145.2 mm[12]SLR24×36 mm1952–1968Early Russian SLRs (Zenit) (not to be confused with M39×26tpi and M39×1/28,8)
M42×145.46 mmSLR24×36 mm1949–Pentacon, Pentax, Contax S, Praktica, Zeiss ZS, Zenit (not to be confused with T-mount, which is M42×0.75)
Pentax K-mount45.46 mmSLR / Mirrorless24×36 mm1975–141[13]10583lens count only for Pentax-branded lenses
Contax C/Y-mount45.50 mmSLR24×36 mm1974–20052453
Petri Bayonet45.50 mmSLR24×36 mm
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-mount45.8 mmSLR24×36 mm1(measured); 230AF etc.
Olympus OM-mount46.00 mmSLR24×36 mm1972–20023814
Nikon F-mount46.50 mmSLR24×36 mm / APS-C1959–213117Only Nikon manufactured lenses counted. Nikon claims that there is over 400 Nikkor lens models manufactured. [14]
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)
Contax N-mount48.00 mmSLR24×36 mm2000–20054501
Arri STD52.00 mmcine
Arri B52.00 mmcine
Arri PL52.00 mmcine
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
Panavision PV-mount57.15 mmcine1972–35 mm & 16mm
OCT-1961.00 mmcine
Mamiya 64563.30 mmSLR6×4.5 cm
Novoflex A-mount63.3 mmSLR(measured) "A"-type adapters for follow-focus system
Contax 64564.00 mmSLR6×4.5 cm
Pentax 64570.87 mmSLR6×4.5 cm1984–
Rollei SLX74.00 mmSLR6×6 cm–2005
Pentacon Six74.1 mmSLR6×6 cm1956–1992
Hasselblad 2000 & 50074.90 mmSLR
Hasselblad 1000F & 1600F82.10 mmSLR
Pentax 6×784.95 mm or 85.00 mmSLR6×7 cm1969–1999
Rollei SL66102.80 mmSLR6×6 cm
Mamiya RZ67105 mmSLR6×7 cm
Mamiya RB67111 mmSLR6×7 cm

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. The most common mount is the Arri PL mount with an FFD of 52.00 mm. The Russian OCT-19 has an FFD of 61.00 mm. C-mount (Bolex, éclair and Bell & Howell) has 17.52 mm. 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 groundglass (or both) that are misset.

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 groundglass, whereas the actual flange focal depth to the aperture plate will in fact be ~0.02 mm less.

See also

References

  1. ↑ pentax.jp
  2. ↑ Hornberg, Alexander (2007-02-27). Handbook of Machine Vision. John Wiley & Sons. ISBN 9783527610143.
  3. ↑ "CS-Mount | Edmund Optics". www.edmundoptics.com. Retrieved 2018-07-28.
  4. ↑ "Flangeback Distances | Universe Optics". Universe Optics. Retrieved 2018-07-28.
  5. ↑ https://www.dpreview.com/news/2095513456/dji-launches-zenmuse-x7-super-35mm-camera-module-with-raw-video-capture
  6. ↑
  7. ↑ http://www.ikegami.com/cb/products/pdf/tech/lensmount.pdf
  8. 1 2
  9. ↑ http://photo.net/nikon-camera-forum/00Zu0J
  10. ↑ 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.
  11. ↑ Wrotniak, J. Andrzej
  12. ↑ Zenit's mount history: M39x1/45,2
  13. ↑ Pentax Lens Search | PentaxForums.com
  14. ↑ [https://www.nikonusa.com/en/learn-and-explore/a/products-and-innovation/nikon-f-mount.html
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