Flange Focal Distance

The Flange Focal Distance or Flange Distance (or flange focal depth, flange back distance, flange focal length, back focus, or register) of a camera refers to the distance from the mounting flange (the metal ring on the camera body where the lens is attached) to the film plane or image sensor. This distance is usually specified in millimeters.

In other words, the flange focal distance is the distance between the rear surface of a camera lens (where it mounts to the camera) and the camera’s image sensor when the lens is focused at infinity.

Film Plane Indicator on a Canon AE-1
Film Plane Indicator on a Canon AE-1

Depending on the manufacturer a camera body may have a mark that indicates where the film or sensor plane is. It is signified by a circle with a line through it.

For Canon 35mm film cameras, such as the Canon AE-1, the mark is to the left of the prism. The distance from that mark to the front of the lens mark represents the flange focal distance.

Focal Plane Mark on a Nikon D750 DSLR
Focal Plane Mark on a Nikon D750

Example shown on a Nikon D750 DSLR. The digital camera obviously doesn’t use film, so Nikon referrers to it as the focal plane mark.

Flange Distance as Shown on a Minolta SRT-101
The Distance Between the Red and Blue Lines is the Flange Distance

The flange distance is important because it determines which lenses can be adapted for use with other cameras. For example, if the flange focal distance of a lens is longer than that of a camera, it can be possible to use an adapter to fit the lens to the camera. The extra distance can provide enough room for the physical coupling of the second lens mount.

However, if the flange focal distance of a lens is shorter than that of the camera, the lens cannot be adapted to the camera without either modifications to the lens or camera, or an additional lens in the adapter to correct the optical path. This is because the lens would need to be placed inside the camera body to achieve focus at infinity.

Adapters that use a correcting lens should generally be avoided. The optics on these adapters are of poor optical quality and will severly degrade the image quality.

Different camera systems have different standard flange focal distances. For example, as of my knowledge cutoff in September 2021, the Canon EOS EF mount has an flange focal distance of 44mm, Nikon F mount has an flange focal distance of 46.5mm, and the Sony E mount has an FFD of 18mm.

Vintage 35mm film lenses are easily adapted onto modern mirrorless cameras. Simple adapters are enough to allow vintage lenses to work because they have physical aperture rings.

Lenses without physical aperture rings require “smart adapters” to provide electrical contacts so that the aperture of a lens can be controlled. For instance adapting a Canon EOS lens onto a Micro Four Thirds camera body.

Minolta Auto Bellows Rokkor X 100mm f/4 Lens
Minolta Auto Bellows Rokkor X 100mm f/4 Lens

There are some lens adapters that do not include optics to correct for infinity focus that are for mounts with a longer flange distance. One that I found was a Minolta MD-mount to Nikon F-mount.

These can be useful for macro photography for attaching a lens onto a bellows. In my instance I wanted to attach a Minolta bellows lens onto a Nikon PB-4 bellows.

Mount Flange Focal Distance Type Format
Samsung NX mini 6.95 mm Mirrorless 1"
Pentax Q-mount 9.2 mm Mirrorless 1/2.3"
M58×0.75 mm mount 12 mm Industrial 24×36 mm
D-mount 12.29 mm cine 8 mm
CS-mount 12.526 mm TV 1/4", 1/3", 1/2"
Nikon Z-mount 16 mm Mirrorless 24×36 mm
DJI DL-mount 16.84 mm Mirrorless Super 35
Nikon 1-mount 17.00 mm Mirrorless CX
C-mount 17.526 mm cine / TV 8 mm, 16 mm, 1/3", 1/2", 2/3", 1", 4/3"
Fujifilm X-mount 17.7 mm Mirrorless APS-C
Canon EF-M mount 18.00 mm Mirrorless APS-C
Sony E-mount 18.00 mm Mirrorless APS-C & Full Frame
24×36 mm (FE) - - -
Sony FZ-mount 19.00 mm cine Super 35
Micro Four Thirds System 19.25 mm Mirrorless 4/3"
Hasselblad XCD mount 18.14 mm Mirrorless Medium Format (127) 43.8×32.9 mm
Canon RF mount 20.00 mm Mirrorless 24×36 mm
Leica L-Mount (formerly CL-mount) 20.00 mm Mirrorless 24×36 mm, APS-C
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
Fujifilm G-mount 26.7 mm Mirrorless Medium Format (127) 43.8×32.9 mm
Pentax Auto 110 27.00 mm SLR 13×17 mm
RED ONE interchangeable mount 27.30 mm cine -
Leica M-mount 27.80 mm Mirrorless 24×36 mm
Nikonos 28.00 mm underwater 24x36 mm
M39 lens mount (M39x26tpi mount) 28.80 mm Mirrorless 24×36 mm
M39 lens mount (M39×1/28.8 mount) 28.80 mm Mirrorless 24×36 mm
Contax G-mount 29.00 mm Mirrorless 24×36 mm
Olympus PEN F (film) 28.95 mm SLR 18×24 mm
Hasselblad XPan 34.27 mm Mirrorless 24×36 mm & 24×65mm
Contax RF-mount 34.85 mm Mirrorless 24×36 mm
Nikon S-mount 34.85 mm Mirrorless 24×36 mm
1/2" TV bayonet mount 35.74 mm TV 1/2" 3-CCD
Minolta V-mount 36.00 mm SLR APS-H
Sony 1/2" TV bayonet mount 38.00 mm TV 1/2" 3-CCD
Olympus Four Thirds System 38.67 mm SLR 4/3"
Aaton mount 40.00 mm cine 16mm/S16
Panavision SP70 mount 38.00 mm cine -
Konica F-mount 40.50 mm SLR 24×36 mm
Konica AR-mount 40.50 mm SLR 24×36 mm
Canon FL-mount 42.00 mm SLR 24×36 mm
Canon FD-mount 42.00 mm SLR 24×36 mm
Start (Soviet camera) 42.00 mm SLR
Minolta SR-mount 43.50 mm SLR 24×36 mm
Fujica X-mount 43.50 mm SLR 24×36 mm
Pentaflex (16 mm cameras) 44.00 mm cine
Canon EF-mount 44.00 mm SLR 24×36 mm
Canon EF-S-mount 44.00 mm SLR APS-C
Praktica B-mount 44.40 mm SLR 24×36 mm
Sigma SA-mount 44.00 mm SLR 24×36 mm
Arri LPL 44.00 mm cine 25.54x36.70 mm
Minolta/Konica Minolta/Sony A-mount 44.50 mm SLR 24×36 mm
Minolta/Konica Minolta/Sony A-mount (APS-C) 44.50 mm SLR APS-C
Rollei QBM 44.50 mm SLR 24×36 mm
Samsung Kenox mount 44.50 mm SLR 24×36 mm
Exakta 44.7 mm SLR 24×36 mm
M39x1 45.20 mm SLR 24×36 mm
M37×1 45.46 mm SLR 24×36 mm
M42×1 45.46 mm SLR 24×36 mm
Pentax K-mount 45.46 mm SLR 24×36 mm
Contax/Yashica (C/Y)-mount 45.50 mm SLR 24×36 mm
Petri Bayonet 45.50 mm SLR 24×36 mm
Mamiya Z 45.50 mm SLR 24×36 mm
Kodak Retina DKL-mount 45.7 mm SLR 24×36 mm / 28×28 mm
Voigtländer Bessamatic DKL-mount 45.7 mm SLR 24×36 mm
Braun Paxette Reflex DKL-mount 45.7 mm SLR / Mirrorless 24×36 mm
Voigtländer Vitessa T DKL-mount 45.7 mm Mirrorless 24×36 mm
Yashica MA-mount 45.80 mm SLR 24×36 mm
Olympus OM-mount 46.00 mm SLR 24×36 mm
Nikon F-mount 46.50 mm SLR 24×36 mm / APS-C
Leica R-mount 47.00 mm SLR 24×36 mm
KMZ Zenit DKL-mount 47.58 mm SLR 24×36 mm
B4-mount 48.00 mm TV 2/3" 3-CCD (9.6×5.4 mm)
Contax N-mount 48.00 mm SLR 24×36 mm
Tamron Adaptall/Adaptall-2 50.7 mm SLR 24×36 mm
Arri STD 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
Mini T-mount 55.00 mm SLR 24×36 mm
T-mount 55.00 mm SLR 24×36 mm
YS mount 55.00 mm SLR 24×36 mm
Mamiya 6 56.20 mm Mirrorless 6×6 cm
Panavision PV-mount 57.15 mm cine
Mamiya 7 59.00 mm Mirrorless 6×7 cm
OCT-19 61.00 mm cine
Hasselblad H-mount 61.63 mm SLR 6×4.5 cm
Mamiya 645 63.30 mm SLR 6×4.5 cm
Novoflex A-mount 63.3 mm SLR
Contax 645 64.00 mm SLR 6×4.5 cm
Zenza Bronica ETR 69.00 mm SLR 6×4.5 cm
Pentax 645 70.87 mm SLR 6×4.5 cm
Rollei SLX 74.00 mm SLR 6×6 cm
Pentacon Six 74.1 mm SLR 6×6 cm
Hasselblad V-mount 74.90 mm SLR 6×6 cm
Kowa Six/Super 66 79.00 mm SLR 6×6 cm
Hasselblad 1000F & 1600F 82.10 mm SLR 6×6 cm
Salyut/Kiev mount 82.10 mm SLR 6×6 cm
Pentax 6×7 84.95 mm or 85.00 mm SLR 6×7 cm
Zenza Bronica SQ 85.00 mm SLR 6×6 cm
Zenza Bronica GS 85.00 mm SLR 6×7 cm
Zenza Bronica S2A 101.70 mm SLR 6×6 cm
Rollei SL66 102.80 mm SLR 6×6 cm
Mamiya RZ 105.00 mm SLR 6×7 cm
Mamiya RB 112.00 mm SLR 6×7 cm