Flange focal distance explained

Flange focal distance should not be confused with front 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.

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.

width=250	Mount	width=100 data-sort-type="number"	Flange focal distance	Type	Format	Production	Prime lenses	Zoom lenses	Wide/tele converters	Mount converters	Comments
	6.95 mm	Mirrorless	1"	2014–2015	2	1
	9.2 mm^[2]	Mirrorless	1/2.3" (6.17×4.55 mm) / 1/1.7"	2011–2019	data-sort-value="5"	5	data-sort-value="3"	3	data-sort-value="0"	0	data-sort-value="1"	1
M58×0.75 mm mount	12 mm	Industrial	24×36 mm						Industrial area and line scan cameras
	12.29 mm	cine	8 mm						(8 mm movie cameras)
	12.526 mm^[3] ^[4] ^[5]	TV	1/4", 1/3", 1/2"						(surveillance cameras)
	16 mm	Mirrorless	24×36 mm	2018–	19	11		1
			APS-C (DX)	2018–	1	4	2		Can use any of the 24x36 mm lenses and the FTZ/FTZ II mount adaptor.
DJI DL-mount	16.84^[6]	Mirrorless	Super 35	2017–	4	0
	17.00 mm^[7]	Mirrorless	CX	2011–2018	3	8		1
	17.526 mm^[8] ^[9]	cine / TV	8 mm, 16 mm, 1/3", 1/2", 2/3", 1", 4/3"	~1926–					(Bolex, Eclair and Bell & Howell)
	17.7 mm	Mirrorless	APS-C	2012–			2	1^[10]
	18.00 mm	Mirrorless	APS-C	2012–			0
	18.00 mm	Mirrorless	APS-C	2010–	data-sort-value="17"		data-sort-value="24"		data-sort-value="8"		data-sort-value="4"		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–	data-sort-value="17"		data-sort-value="24"		data-sort-value="8"		data-sort-value="4"		Lens count doesn't include 3rd party products.
	19.00 mm	cine	Super 35	2011–	0	2	0	3
			24×36 mm	2015–	1	2
	19.25 mm	Mirrorless	4/3"	2008–			1	1
	18.14 mm (+0.05/-0.00)	Mirrorless	Medium Format (127) 43.8×32.9 mm	2017–	13	1		3	for Hasselblad X System
	20.00 mm	Mirrorless	24×36 mm	2018–	12	11		3
Leica L-Mount (formerly CL-mount)	20.00 mm	Mirrorless	24×36 mm, APS-C	2014–	19	12
	25.00 mm	TV	1/3" 3-CCD (5.24×2.94 mm)
	25.50 mm	Mirrorless	APS-C	2010–2015	8	8
	26.7 mm	Mirrorless	Medium Format (127) 43.8×32.9 mm	2017–	7	2	1		for Fujifilm GFX series cameras
	27.00 mm	SLR	13×17 mm	1978–1985	5	1	0	0
	27.30 mm	cine
	27.8 (inner rails) <-> 27.95 (outer rails) mm	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)
	28.00 mm^[11]	underwater	24x36 mm	1963-2001	6	0	0	0	this is the underwater scale focusing camera
	28.80 mm	Mirrorless	24×36 mm						Leica M39×26tpi aka LTM (Leica Thread Mount) aka L39 (not to be confused with M39×1)
	28.80 mm^[12]	Mirrorless	24×36 mm	1948-1978					Zorki M39×1/28.8 for Zorki cameras (not to be confused with M39×1 and M39x26tpi)
	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
	34.27 mm	Mirrorless	24×36 mm & 24×65 mm	1998–2003	3	0	0	0	Identical to Fujifilm TX series cameras and mount
	34.85 mm	Mirrorless	24×36 mm
	34.85 mm	Mirrorless	24×36 mm	1947–2005
	35.74 mm	TV	1/2" 3-CCD						JVC, Hitachi, Panasonic, others, but not Sony
	36.00 mm	SLR	APS-H	1996–1999	3	5	0	1	Vectis S-1, Vectis S-100, Dimâge RD 3000
	38.00 mm	TV	1/2" 3-CCD
	38.67 mm	SLR	4/3"	2003–2017	12	30	2
Aaton mount	40.00 mm	cine	16 mm/S16
	38.00 mm	cine		2018–					35 mm & 65 mm
	40.50 mm	SLR	24×36 mm	1960–1965	17	0	0	0
	40.50 mm	SLR	24×36 mm	1965–1988	36	16	1	0
	42.00 mm	SLR	24×36 mm	1964–1971
	42.00 mm	SLR	24×36 mm	1971–1990	107	34
Start (Soviet SLR)	42.00 mm	SLR		1958–1964
	43.50 mm	SLR	24×36 mm	1958–2001				6
	43.50 mm	SLR	24×36 mm	1980–1985
	44.00 mm	cine
	44.00 mm	SLR	24×36 mm / APS-H / APS-C	1987–	47	64
	44.00 mm	SLR	APS-C	2003–			0	0
	44.40 mm	SLR	24×36 mm	1978–1990
	44.00 mm	SLR	24×36 mm / APS-C	1992–	14	19	2	4
Arri LPL	44.00 mm	cine	25.54x36.70 mm	2018-					for Arri Alexa LF
	44.50 mm	SLR	24×36 mm	1985–	data-sort-value="62"	42+0+17	data-sort-value="81"	50+2+13	data-sort-value="8"	6+0+2	2+0+0
			APS-C	2004–	data-sort-value="63"	0+0+3	data-sort-value="80"	0+3+13	data-sort-value="8"	0+0+0	0+0+0
	44.50 mm^[13]	SLR	24×36 mm	1970–					Rollei, Voigtländer
	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
	44.7 mm^[14]	SLR	24×36 mm	1936–1969
M39x1	45.20 mm^[15]	SLR	24×36 mm	1952–1968					Early Russian SLRs (Zenit) (not to be confused with M39×26tpi and M39×1/28,8)
	45.46 mm	SLR	24×36 mm	1952-1957					Asahiflex I, Asahiflex IA (Tower 23), Asahiflex IIB (Tower 23/24), Asahiflex IIA (Tower 22)
	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)
	45.46 mm	SLR / Mirrorless	24×36 mm / APS-C	1975–	147^[16]	108	8	3	Used also by some Samsung, Ricoh, Chinon, Agfa, Vivitar, Petri and KMZ (Zenit) cameras. Lens count only for Pentax-branded lenses.
	45.50 mm	SLR	24×36 mm	1974–2005	24	5	3		Used by some Contax and Yashica SLR cameras
	45.50 mm	SLR	24×36 mm						Petri SLRs 1960-77.
	45.50 mm	SLR	24×36 mm	1980–
	45.7 mm	SLR / Mirrorless	24×36 mm / 28×28 mm	1958–1977	data-sort-value="18"		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
	45.7 mm	SLR	24×36 mm	1958–1967	data-sort-value="13"			0	0	DKL variants used by Bessamatic, Bessamatic deLuxe, Bessamatic m, Bessamatic CS, Ultramatic, Ultramatic CS
	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
	45.7 mm	Mirrorless	24×36 mm		data-sort-value="4"	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.
	46.00 mm	SLR	24×36 mm	1972–2002	38	14
	46.50 mm	SLR	24×36 mm / APS-C	1959–					Used by some Kiev F-mount cameras. Only Nikon manufactured lenses counted. Nikon claims that there is over 400 Nikkor lens models manufactured.^[17]
	47.00 mm	SLR	24×36 mm	1964–2009
	47.58 mm	SLR	24×36 mm	1964–1968			0	0	Zenit/Зенит 4/5/6 "Байонет Ц", an unofficial DKL-mount variant
	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.
	48.00 mm	SLR	24×36 mm	2000–2005	4	5	0	1
	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.
	52.00 mm	cine
	52.00 mm	cine
	52.00 mm	cine
	53.00 mm	SLR	45×30 mm	1996–
	55.00 mm	SLR	24×36 mm	1957–1962					Taisei, M37×0.75
	55.00 mm	SLR	24×36 mm	1962–					Tamron T-400, M42×0.75 (not to be confused with M42×1)
	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
	56.20 mm	Mirrorless	6×6 cm	1989–1995	3	0	0	0	Rangefinder camera system, flange focal distance might not be precise.^[18]
	57.15 mm	cine		1972–					35 mm & 16 mm
	59.00 mm	Mirrorless	6×7 cm	1995–2014	6	0	0	0	Rangefinder camera system
	61.00 mm	cine
	61.63 mm	SLR	6×4.5 cm	2002–					for Hasselblad H System
	63.30 mm	SLR	6×4.5 cm	1975–
A-mount	63.3 mm	SLR							(measured) "A"-type adapters for follow-focus system
	64.00 mm	SLR	6×4.5 cm	1999–
	69.00 mm	SLR	6×4.5 cm	1976–2004	17	2
	70.87 mm	SLR	6×4.5 cm	1984–	25	8	2	2
	74.00 mm	SLR	6×6 cm	1976–2005
	74.1 mm	SLR	6×6 cm	1956–1992					Used also by Exakta 66 and Kiev 60 series cameras
	74.90 mm	SLR	6×6 cm	1957–2013					for Hasselblad V system
	79.00 mm	SLR	6×6 cm	1968–1974	9	0
	82.10 mm	SLR	6×6 cm	1948–1957
	82.10 mm	SLR	6×6 cm	1972–1980					Used by Salyut-S/Салют-C, Zenit/Zenith-80, Kiev 88 cameras
	84.95 mm^[19] or 85.00 mm	SLR	6×7 cm	1969–1999	25	2	3
	85.00 mm	SLR	6×6 cm	1980–2003	14
	85.00 mm	SLR	6×7 cm	1983–2002	9	0	2
	101.70 mm	SLR	6×6 cm	1959–1980
	102.80 mm	SLR	6×6 cm	1966–1992
	105.00 mm	SLR	6×7 cm	1982–
	112.00 mm	SLR	6×7 cm	1970–
	62.22 mm	SLR	24×24 mm	1968-1969
16-SP	52 mm^[20]	Cine	16 mm	1965-1991					Used on the Soviet Kinor 16 and Krasnogorsk cameras
Kiev-16U	31 mm^[21]	Cine	16 mm		3				Used on the Soviet Kiev-16U camera
1KSR-1M	57 mm^[22]	Cine	35 mm						Used on the Soviet Konvas-1M, 7M, Automat cameras
1KSR-2M	61 mm	Cine	35 mm						Used on the Soviet Konvas-2M, 8M, Kinor-35 cameras

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

• List of lens mounts

References

• Markerink, Willem-Jan. Camera Mounts & Registers . Retrieved on November 6, 2005.

Notes and References

1. Web site: FOCUS BACK ON BACK FOCUS. 30 May 2009 .
2. http://www.pentax.jp/english/news/2011/201109.html
3. Book: Hornberg, Alexander. Handbook of Machine Vision. 2007-02-27. John Wiley & Sons. 9783527610143. en.
4. Web site: CS-Mount Edmund Optics. www.edmundoptics.com. en. 2018-07-28.
5. News: Flangeback Distances Universe Optics. Universe Optics. 2018-07-28. en-US.
6. Web site: DJI launches Zenmuse X7 Super 35mm camera module with Raw video capture.
7. Web site: Camera Mounts Sorted by Register.
8. Web site: main difference about C-mount vs. CS-mount . 2024-08-01.
9. Web site: C-Mount vs. CS-Mount. ikegami.com. 4 August 2023.
10. Web site: Lens accessories | Accessories. FUJIFILM X Series & GFX – Global. 11 January 2024 .
11. Web site: Nikonos Lenses on Nikon dSLR?. Photo.net Photography Forums. 21 January 2012 .
12. Web site: The Camera ZORKI Instruction Manual?.
13. 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.
14. http://www.wrotniak.net/photo/exakta/lenses.html
15. http://www.zenitcamera.com/archive/history/mounts.html#z39
16. Web site: Zoom Lenses | PentaxForums.com. www.pentaxforums.com.
17. https://www.nikonusa.com/en/learn-and-explore/a/products-and-innovation/nikon-f-mount.html Nikon F-Mount
18. https://www.kenrockwell.com/mamiya/6.htm
19. https://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html
20. Web site: 16-SP (Krasnogorsk-2) adapters . 3 May 2024.
21. Web site: Industar-50 KIEV 16mm lens C mount ? . 2024-05-03 . forum.mflenses.com.
22. Web site: Flange Focal Distances . dead . https://web.archive.org/web/20060518183608/http://rafcamera.com/info/ffd.htm . 2006-05-18 . 2024-05-03 .