Engineering:Flange focal distance

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Short description: Property of a lens mount system
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), 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.

The flange focal distance is a fixed mechanical specification of a given camera system, and it must be manufactured to a precision of hundredths of a millimetre—even small deviations can prevent lenses from achieving accurate focus across all focal lengths. This value should not be confused with depth of field, which refers to the range of distances in front of the camera that appear acceptably sharp during image capture.

Lenses can be adapted from one mount (and respective FFD) to another using a lens adapter. 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 mini 6.95 mm Mirrorless 1" 2014–2015 2 1 1
Pentax Q-mount 9.2 mm[2] Mirrorless 1/2.3" (6.17×4.55 mm) / 1/1.7" 2011–2019 5 3 0 1
M58×0.75 mm mount 12 mm Industrial 24×36 mm Industrial area and line scan cameras
D-mount 12.29 mm cine 8 mm (8 mm movie cameras)
CS-mount 12.526 mm[3][4][5] TV 1/4", 1/3", 1/2" (surveillance cameras)
Nikon Z-mount 16 mm Mirrorless 24×36 mm (FX) 2018– 25 17 2 1 Lens count doesn't include 3rd party products and optically identical "SE" versions.
APS-C (DX) 2018– 2 6 Lens count doesn't include 3rd party products and optically identical "SL" versions. Can use any of the 24x36 mm (FX) lenses and the FTZ/FTZ II mount adaptor.
DJI DL-mount 16.84 mm[6] Mirrorless Super 35 2017– 6 1 For use on aerial drone and gimbal cameras.
Nikon 1-mount 17.00 mm[7] Mirrorless CX 2011–2018 3 8 1
C-mount 17.526 mm[8] 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– 23 14 2 1[9]
Canon EF-M-mount 18.00 mm Mirrorless APS-C 2012– 3 5 0 1
Sony E-mount 18.00 mm Mirrorless APS-C 2010– 6 14 4 2

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– 22 17 4 3

Lens count doesn't include 3rd party products.

Sony FZ-mount 19.00 mm cine Super 35 2011– 0 2 0 3
24×36 mm 2015– 1 2
Micro Four Thirds System 19.25 mm Mirrorless 4/3" 2008– 37 28 1 1
Hasselblad XCD mount 18.14 mm (+0.05/-0.00) Mirrorless Medium Format (127) 43.8×32.9 mm 2017– 13 1 3 for Hasselblad X System
Canon RF mount 20.00 mm Mirrorless 24×36 mm 2018– 12 11 3
L-Mount[10] (Leica, Panasonic Lumix, Sigma, DJI, et al.) 20.00 mm Mirrorless 24×36 mm, APS-C 2014– 19 12 The members of the L-mount alliance are Leica Camera, SIGMA, Panasonic, Ernst Leitz Wetzlar GmbH, DJI, Astrodesign, SIRUI, LK Samyang, Blackmagic Design, and Viltrox
LUMIX Panasonic[11] 20.00 mm Mirrorless 24×36 mm, APS-C 2015– 8 9 7 L-mount system
JVC 1/3" bayonet mount 25.00 mm TV 1/3" 3-CCD (5.24×2.94 mm)
Samsung NX-mount 25.50 mm Mirrorless APS-C 2010–2015 8 8
Fujifilm G-mount 26.7 mm Mirrorless Medium Format (127) 43.8×32.9 mm 2017– 7 2 1 for Fujifilm GFX series cameras
Pentax Auto 110 27.00 mm SLR 13×17 mm 1978–1985 5 1 0 0
RED ONE interchangeable mount 27.30 mm cine
Leica M-mount 27.8 (inner rails) <-> 27.95 (outer rails) mm[9] 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)
Nikonos 28.00 mm[12] underwater 24x36 mm 1963-2001 6 0 0 0 this is the underwater scale focusing camera
M39×26tpi mount 28.80 mm Mirrorless 24×36 mm Leica M39×26tpi aka LTM (Leica Thread Mount) aka L39 (not to be confused with M39×1)
M39×1/28.8 mount 28.80 mm[13] Mirrorless 24×36 mm 1948-1978 Zorki M39×1/28.8 for Zorki cameras (not to be confused with M39×1 and M39x26tpi)
Contax G-mount 29.00 mm Mirrorless 24×36 mm 1994–2005 6 1 0 1
Olympus PEN F (film) 28.95 mm SLR 18×24 mm 1963–1972 16 2
Hasselblad XPan 34.27 mm Mirrorless 24×36 mm & 24×65 mm 1998–2003 3 0 0 0 Identical to Fujifilm TX series cameras and mount
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, Dimâge RD 3000
Sony 1/2" TV bayonet mount 38.00 mm TV 1/2" 3-CCD
Olympus Four Thirds System 38.67 mm SLR 4/3" 2003–2017 12 30 2
Aaton mount 40.00 mm cine 16 mm/S16
Panavision SP70-mount 38.00 mm cine 2018– 35 mm & 65 mm
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 1980–1985
Pentaflex (16 mm cameras) 44.00 mm cine
Canon EF-mount 44.00 mm SLR 24×36 mm / APS-H / APS-C 1987– 47 64
Canon EF-S-mount 44.00 mm SLR APS-C 2003– 2 9 0 0
Praktica B-mount 44.40 mm SLR 24×36 mm 1978–1990
Sigma SA-mount 44.00 mm SLR 24×36 mm / APS-C 1992– 14 19 2 4
M39x1 44.00 mm[14] Mirrorless 24×36 mm 1950s Braun Paxette rangefinder cameras
Kiev Automat 44.00 mm[15] SLR 24x36 mm 1960s-1980s 6[15] 1[15]
Arri LPL 44.00 mm cine 25.54x36.70 mm 2018- for Arri Alexa LF
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
Rollei QBM 44.50 mm[16] SLR 24×36 mm 1970– Rollei, Voigtländer
Samsung Kenox mount 44.50 mm SLR 24×36 mm 1997–2002 1 2 (3?) 0 0 Although designed in 1990s, mount is manual-focus only; lenses mount and lock on a slightly modified Minolta A-mount adapters
Exakta 44.7 mm[17] SLR 24×36 mm 1936–1969
M39x1 45.20 mm[18] SLR 24×36 mm 1952–1968 Early Russian SLRs (Zenit) (not to be confused with M39×26tpi and M39×1/28,8)
M37×1 45.46 mm SLR 24×36 mm 1952-1957 Asahiflex I, Asahiflex IA (Tower 23), Asahiflex IIB (Tower 23/24), Asahiflex IIA (Tower 22)
M42×1 45.46 mm SLR 24×36 mm 1949– Pentacon, Pentax, Contax S, Praktica, Zeiss ZS, Zenit, many others (not to be confused with T-mount, which is M42×0.75)
Pentax K-mount 45.46 mm SLR / Mirrorless 24×36 mm / APS-C 1975– 147[19] 108 8 3 Used also by some Samsung, Ricoh, Chinon, Agfa, Vivitar, Petri and KMZ (Zenit) cameras. Lens count only for Pentax-branded lenses.
Contax C/Y-mount 45.50 mm SLR 24×36 mm 1974–2005 24 5 3 Used by some Contax and Yashica SLR cameras
Petri Bayonet 43.50 mm SLR 24×36 mm Petri SLRs 1960-77.
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 45.80 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– 213 117 Used by some Kiev F-mount cameras. Only Nikon manufactured lenses counted. Nikon claims that there is over 400 Nikkor lens models manufactured.[20]
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-mount 48.00 mm TV 2/3" 3-CCD (9.6×5.4 mm) 1992– Mount was in use since at least 1978, wasn't officially standardized until 1992.
Contax N 48.00 mm SLR 24×36 mm 2000–2005 4 5 0 1
Tamron Adaptall/Adaptall-2 50.7 mm SLR 24×36 mm 1973-2006 14 29 3 26 No camera uses Adaptall lenses natively, intended to be used with mount adapters. Many lenses have revisions, only original optical formulas are counted.
Arri Standard 52.00 mm cine
Arri B 52.00 mm cine
Arri PL 52.00 mm cine
Leica S-mount 53.00 mm SLR 45×30 mm 1996–
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
Mamiya 6 56.20 mm Mirrorless 6×6 cm 1989–1995 3 0 0 0 Rangefinder camera system, flange focal distance might not be precise.[21]
Panavision PV-mount 57.15 mm cine 1972– 35 mm & 16 mm
Mamiya 7 59.00 mm Mirrorless 6×7 cm 1995–2014 6 0 0 0 Rangefinder camera system
OCT-19 61.00 mm cine
Hasselblad H-mount 61.63 mm SLR 6×4.5 cm 2002– for Hasselblad H System
Mamiya 645 63.30 mm SLR 6×4.5 cm 1975–
Novoflex [de; de] A-mount 63.3 mm SLR (measured) "A"-type adapters for follow-focus system
Contax 645 64.00 mm SLR 6×4.5 cm 1999–
Zenza Bronica ETR 69.00 mm SLR 6×4.5 cm 1976–2004 17 2
Pentax 645 70.87 mm SLR 6×4.5 cm 1984– 25 8 2 2
Rollei SLX 74.00 mm SLR 6×6 cm 1976–2005
Pentacon Six 74.1 mm SLR 6×6 cm 1956–1992 Used also by Exakta 66 and Kiev 60 series cameras
Hasselblad V-mount 74.90 mm SLR 6×6 cm 1957–2013 for Hasselblad V system
Kowa Six/Super 66 79.00 mm SLR 6×6 cm 1968–1974 9 0
Hasselblad 1000F & 1600F 82.10 mm SLR 6×6 cm 1948–1957
Salyut/Kiev mount 82.10 mm SLR 6×6 cm 1972–1980 Used by Salyut-S/Салют-C, Zenit/Zenith-80, Kiev 88 cameras
Pentax 6×7 84.95 mm[22] or 85.00 mm SLR 6×7 cm 1969–1999 25 2 3
Zenza Bronica SQ 85.00 mm SLR 6×6 cm 1980–2003 14
Zenza Bronica GS 85.00 mm SLR 6×7 cm 1983–2002 9 0 2
Zenza Bronica S2A 101.70 mm SLR 6×6 cm 1959–1980
Rollei SL66 102.80 mm SLR 6×6 cm 1966–1992
Mamiya RZ 105.00 mm SLR 6×7 cm 1982–
Mamiya RB 112.00 mm SLR 6×7 cm 1970–
Ricoh 126C-Flex 62.22 mm SLR 24×24 mm 1968-1969
16-SP 52 mm[23] Cine 16 mm 1965-1991 Used on the Soviet Kinor 16 and Krasnogorsk cameras
Kiev-16U 31 mm[24] Cine 16 mm 3 Used on the Soviet Kiev-16U camera
1KSR-1M 57 mm[25] Cine 35 mm Used on the Soviet Konvas-1M, 7M, Automat cameras
1KSR-2M 61 mm[25] Cine 35 mm Used on the Soviet Konvas-2M, 8M, Kinor-35 cameras
Vivitar TX 56.25 mm SLR 24×36mm 1976- 10 10 Generic mount used to be attached on many cameras thanks to differents adapters

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". 30 May 2009. https://thecinelens.com/2009/05/30/focus-on-back-focus/. 
  2. ↑ [1] pentax.jp
  3. ↑ Hornberg, Alexander (2007-02-27) (in en). Handbook of Machine Vision. John Wiley & Sons. ISBN 9783527610143. https://books.google.com/books?id=HEy4UBoGF2UC&q=cs-mount+%2212.526%22&pg=PA49. 
  4. ↑ "CS-Mount | Edmund Optics" (in en). https://www.edmundoptics.com/resources/glossary/c/cs-mount/. 
  5. ↑ "Flangeback Distances | Universe Optics" (in en-US). Universe Optics. http://www.universeoptics.com/optical-lens-design/flangeback-distances/. 
  6. ↑ "DJI launches Zenmuse X7 Super 35mm camera module with Raw video capture". https://www.dpreview.com/news/2095513456/dji-launches-zenmuse-x7-super-35mm-camera-module-with-raw-video-capture. 
  7. ↑ "Camera Mounts Sorted by Register". https://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html. 
  8. ↑ "C-Mount vs. CS-Mount". https://www.ikegami.com/cb/products/pdf/tech/lensmount.pdf. 
  9. ↑ 9.0 9.1 "Lens accessories | Accessories". 11 January 2024. https://fujifilm-x.com/global/products/accessories/lens-accessories/. 
  10. ↑ "L-mount Alliance Overview". https://l-mount.com/en/overview-213. 
  11. ↑ "LUMIX Panasonic L-mount". https://www.panasonic.com/global/consumer/lumix/s/L-Mount.html. 
  12. ↑ "Nikonos Lenses on Nikon dSLR?". 21 January 2012. https://www.photo.net/discuss/threads/nikonos-lenses-on-nikon-dslr.456898/. 
  13. ↑ "The Camera ZORKI Instruction Manual?". https://www.cameramanuals.org/russian_pdf/zorki.pdf. 
  14. ↑ [2] Discussion of Zenit and Braun Paxette mounts
  15. ↑ 15.0 15.1 15.2 Reinsalu, Armult (1987). "Lisad". in Iho, A (in et). Algajale fotograafile. Reviewed by Kunnar Allikvee, artistic editor H. Puzanov, technical editor K. Kuulmann, proofreaders S. Hiie and M. Mere.. Tallinn: Valgus. p. 177. https://www.librarything.com/work/10549335/t/Algajale-fotograafile. 
  16. ↑ 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.
  17. ↑ [3] Wrotniak, J. Andrzej
  18. ↑ [4] Zenit's mount history: M39x1/45,2
  19. ↑ "Zoom Lenses | PentaxForums.com". https://www.pentaxforums.com/lenssearch/?type=Zoom&inproduction=0. 
  20. ↑ Nikon F-Mount, nikonusa.com
  21. ↑ [5] Ken Rockwell's Mamiya 6 page
  22. ↑ [6] Camera Mounts Sorted by Register
  23. ↑ "16-SP (Krasnogorsk-2) adapters". https://rafcamera.com/adapters/bayonet-adapters/krasnogorsk-2. 
  24. ↑ "Industar-50 KIEV 16mm lens C mount ?". https://forum.mflenses.com/industar-50-kiev-16mm-lens-c-mount-t53620.html#1267043. 
  25. ↑ 25.0 25.1 "Flange Focal Distances". http://rafcamera.com/info/ffd.htm. 



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