Flange focal distance

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

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
Pentax Q-mount 9.2 mm[1] Mirrorless 1/2.3" (6.17×4.55 mm) 2011– 4 2 0 0
1/1.7" (7.44×5.58 mm) 2013– 1 1 0 1
D-mount 12.29 mm cine 8 mm (8 mm movie cameras)
CS-mount 12.50 mm[2] TV 1/4", 1/3", 1/2" (surveillance cameras)
Nikon 1-mount 17 mm[3] Mirrorless CX 2011– 1
C-mount 17.526 mm[2] cine / TV 8 mm, 16 mm, 1/3", 1/2", 2/3", 1", 4/3" ~1926– (Bolex, Eclair and Bell & Howell)
Fujifilm X-mount 17.7 mm Mirrorless APS-C 2012– 8 8 0 1[4]
Canon EF-M-mount 18 mm Mirrorless APS-C 2012– 1 3 0 1
Sony E-mount 18 mm Mirrorless 24×36 mm / APS-C 2010– 6 10 4 2
24×36 mm (FE) 2013– 5 6 2 2
Sony FZ-mount 18 mm cine Super 35 mm 2011– 0 2 0 3
Leica SL-mount (formerly T) 19 mm Mirrorless 24×36 mm / APS-C 2014– 1 3
24×36 mm 2015–
Micro Four Thirds System 19.25 mm Mirrorless 4/3" 2008– 22 17
Samsung NX-mount 25.50 mm Mirrorless APS-C 2010– 5 4
Pentax Auto 110 27 mm SLR 13×17 mm 1978–1985 5 1 0 0
RED ONE interchangeable mount 27.30 mm cine
Leica M-mount 27.80 mm[4] Mirrorless 24×36 mm 1954– aka Voigtländer VM-mount, Epson EM-mount, Zeiss ZM-mount as well as Konica KM-mount (Hexar RF) and Minolta M-mount (CL/CLE)
M39×26tpi mount 28.80 mm Mirrorless 24×36 mm Leica M39×26tpi aka L39 (not to be confused with M39×1)
Contax G-mount 29.00 mm Mirrorless 1994–2005 6 1 0 1
Olympus PEN F 28.95 mm SLR 18 x 24 mm 1963–1972 16 2
Contax RF-mount 34.85 mm Mirrorless 24×36 mm
Nikon S-mount 34.85 mm Mirrorless 24×36 mm 1947–2005
1/2" TV bayonet mount 35.74 mm TV 1/2" 3-CCD JVC, Hitachi, Panasonic, others, but not Sony
Minolta V-mount 36.00 mm SLR APS-H 1996–1999 3 5 0 1 Vectis S-1, Vectis S-100, Dimáge RD-3000
Sony 1/2" TV bayonet mount 38 mm TV 1/2" 3-CCD
Olympus Four Thirds System 38.67 mm SLR 4/3" 2003– 12 30 2
Konica F-mount 40.50 mm SLR 24×36 mm 1960–1965 17 0 0 0
Konica AR-mount 40.50 mm SLR 24×36 mm 1965–1988 36 16 1 0
Canon FL-mount 42.00 mm SLR 24×36 mm 1964–1971
Canon FD-mount 42.00 mm SLR 24×36 mm 1971–1990 107 34
Start (Soviet SLR) 42.00 mm SLR 1958–1964
Minolta SR-mount 43.50 mm SLR 24×36 mm 1958–2001 6
Fujica X-mount 43.50 mm SLR 24×36 mm
Pentaflex (16 mm cameras) 44 mm cine
Canon EF-mount 44.00 mm SLR 24×36 mm / APS-C 1987– 47 64
Canon EF-S-mount 44.00 mm SLR APS-C 2003– 2 9 0 0
Praktica B-mount 44.00 mm SLR 24×36 mm
Sigma SA-mount 44.00 mm SLR 24×36 mm / APS-C 1992– 0
Minolta/Konica Minolta/Sony A-mount 44.50 mm SLR 24×36 mm 1985– 42+0+17 50+2+13 6+0+2 2+0+0
APS-C 2004– 0+0+3 0+3+13 0+0+0 0+0+0
QBM 44.5 mm[5] SLR 24×36 mm Rollei, Voigtländer
Exakta 44.7 mm[6] SLR 24×36 mm 1936–1969
M42×1 45.46 mm SLR 24×36 mm 1949– Pentacon, Pentax, Contax S, Praktica, Zeiss ZS (not to be confused with M42×0.75)
M39x1 45.46 mm SLR 24×36 mm Russian SLRs (not to be confused with M39×26tpi)
Pentax K-mount 45.46 mm SLR / Mirrorless 24×36 mm 1975– 131 77
Contax C/Y-mount 45.50 mm SLR 24×36 mm 1974–2005 24 5 3
Mamiya Z 45.50 mm SLR 24×36 mm 1980–
Kodak Retina DKL-mount 45.7 mm SLR / Mirrorless 24×36 mm / 28×28 mm 1958–1977 12+6 0 0 0 DKL 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-mount 45.7 mm SLR 24×36 mm 1958–1967 11+2 1 0 0 DKL variants used by Bessamatic, Bessamatic deLuxe, Bessamatic m, Bessamatic CS, Ultramatic, Ultramatic CS
Braun Paxette Reflex DKL-mount 45.7 mm SLR / Mirrorless 24×36 mm DKL 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-mount 45.7 mm Mirrorless 24×36 mm 4+? 0 0 0 DKL 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-mount 45.8 mm SLR 24×36 mm 1 (measured); 230AF etc.
Olympus OM-mount 46.00 mm SLR 24×36 mm 1972–2002 38 14
Nikon F-mount 46.50 mm SLR 24×36 mm / APS-C 1959– ? ?
Leica R-mount 47.00 mm SLR 24×36 mm 1964–2009
KMZ Zenit DKL-mount 47.58 mm SLR 24×36 mm 1964–1968 5 1 0 0 Zenit/Зенит 4/5/6 "Байонет Ц", an unofficial DKL-mount variant
B4 2/3" TV bayonet mount[7] 48.00 mm TV 2/3" 3-CCD 1992– Unofficially known as "B4 mount"
Contax N-mount 48.00 mm SLR 24×36 mm 2000–2005 4 5 0 1
Arri STD 52.00 mm cine
Arri B 52.00 mm cine
Arri PL 52.00 mm cine
Mini T-mount 55.00 mm SLR 24×36 mm 1957–1962 Taisei, M37×0.75
T-mount 55.00 mm SLR 24×36 mm 1962– Tamron T-400, M42×0.75 (not to be confused with M42×1)
YS mount 55.00 mm SLR 24×36 mm –1969 Sigma, 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-mount 57.15 mm cine 1972– 35 mm & 16mm
OCT-19 61.00 mm cine
Mamiya 645 63.30 mm SLR 6×4.5 cm
Novoflex A-mount 63.3 mm SLR (measured) "A"-type adapters for follow-focus system
Contax 645 64.00 mm SLR 6×4.5 cm
Pentax 645 70.87 mm SLR 6×4.5 cm 1984–
Rollei SLX 74.00 mm SLR 6×6 cm –2005
Pentacon Six 74.1 mm SLR 6×6 cm 1956–1992
Hasselblad 2000 & 500 74.90 mm SLR
Hasselblad 1000F & 1600F 82.10 mm SLR
Pentax 6×7 84.95 mm or 85.00 mm SLR 6×7 cm 1969–1999
Rollei SL66 102.80 mm SLR 6×6 cm
Mamiya RZ67 105 mm SLR 6×7 cm
Mamiya RB67 111 mm SLR 6×7 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 which 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) which are mis-set.

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. 1 2 http://www.ikegami.com/cb/products/pdf/tech/lensmount.pdf
  3. ↑
  4. 1 2
  5. ↑ 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.
  6. ↑ Wrotniak, J. Andrzej
  7. ↑ ARIB BTA S-1005B
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