Flange Focal Distance is distance from a lens mount flange to focal plane, and this distance is the same, irrespective of the actual focal length as a 10mm lens should focus the rays to the same physical location as does a 600mm lens.

But different cameras have different flange focal distance that makes it impossible to make some adapters. For example, you can't make an adapter between Arri PL and OCT-19 mounts. Or you need to use optical elements like in infinity-allowing M42 to Nikon-F adapter.

I have info on FFD and mount diameter of some movie cameras. Wikipedia has more info.

 

Camera

FFD, mm

Mount diameter, mm

1

1KSR-1M (Konvas-1M,-7M,-Automat)

57±0.01

47

2

1KSR-2M (Konvas-2M,-8M, Kinor-35)

61±0.01

68

3

US-3H

61±0.01

68

4

US-2M

68±0.01

68

5

1-SKL (Temp)

57±0.01

50

6

Arri-2C

52±0.01

41

7

Arri-BL2

52±0.01

41

8

Arri-BL3

52±0.01

54

9

Aaton

40mm ?

?


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