Flange focal distance

Not to be confused with front focal distance.

File:Flange Focal Length (2 types camera).PNG

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	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	TV	1/4", 1/3", 1/2"						(surveillance cameras)
Nikon 1-mount	17 mm	Mirrorless	CX	2011–				1
C-mount	17.526 mm	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
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	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	SLR	24×36 mm						Rollei, Voigtländer
Exakta	44.7 mm	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	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
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
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	108 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

• List of lens mounts

References

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