Flange to Focal Plane Distance

[KirkS]

How does one measure the flange to focal plane distance of a lens? I'm thinking that if I put paper behind the lens, and aim it towards a point of light, the distance from the back of the lens (flange) to the piece of paper would be the same as the flange to focal plane distance. Is that correct?

 

[Derrel]

The best way is to figure out what the MOUNT style is, then look at a chart that lists the distance for various mounts.

 

[SCraig]

There is a mark on top of the camera (a circle with a line through it) that indicates the focal plane. Put a straight edge against the flange and measure to the focal plane mark.

 

[480sparky]

There is a mark on top of the camera (a circle with a line through it) that indicates the focal plane. Put a straight edge against the flange and measure to the focal plane mark.

Or you can just Google it.

System (mount)​	Flange focal distance (mm)​	Note​
Sony E (NEX)	18	Mirrorless (Evil) camera
Micro 4/3 (Micro Four Thirds)	20	Mirrorless (Evil) camera
Samsung NX	25.5	Mirrorless (Evil) camera
4/3 (Four Thirds)	38.67	SLR camera
Sigma SA	44	SLR APS-C camera
Canon EF(-S)	44	SLR 35mm and APS-C camera
Sony A / Minolta A	44.5	SLR 35mm and APS-C camera
Pentax K (KA, KAF)	45.5	SLR 35mm and APS-C camera
Nikon F (FX, DX)	46.5	SLR 35mm and APS-C camera

 

[KirkS]

Yeah, that's great for typical lenses, but I'm trying to figure out an oddity.

It's a Takumar 500mm f/4.5, which by design had interchangeable mounts. The back end of the lens has a bayonet type connection that you could then mount different mounts to. I have been able to confirm that there was an M42 and Nikon mount available, and it seems an FD was also available (but seems to be more uncommon). I happen to have the FD mount connection. Keep in mind, that the lens is not designed to have a 42mm (FD) flange to focal plane distance, but was designed to accommodate various mounts with the adapters. So what I'm trying to figure out is what the actual flange to focal plane distance is of this lens with the FD mount adapter. I have (somewhere) an FD to EF adapter, and even though on an FD-designed lens (designed to have a FtoFP distance of 42mm), I'm thinking that this lens will actually still focus to infinity with the currently installed FD 'tube' and then an FD>EF adapter.

If I could just find my FD>EF adapter, I wouldn't have to ask, but since the adapter is essentially useless, it's buried somewhere, and I have yet to find it after 3 days of looking.

Here are a couple of pics of the removable rear mounting section from the lens. Keep in mind, THIS IS NOT THE LENS; it's only the interchangeable section that was available with different mounts on the back originally.

 

[KirkS]

And this is an example of the lens - http://www.pentaxforums.com/lensreviews/data/25/large/SMC_Takumar_Pentax_500mm.jpg

 

[Derrel]

The flange to focal length distance will be whatever is the proper distance for EACH, INDIVIDUAL MOUNT TYPE. It's not strictly a property of that lens. When the Takumar 500mm lens is fitted with the Nikon mount, the flange to focal plane distance will be...46.5 millimeters. Tamron made multiple series of lenses with interchangeable rear mounting sections, under their Adaptall and Adaptall-II model names. The lens itself does not possess a single, specific "distance"...that's why I said, " Figure out what the MOUNT style is, then look at a chart that lists the distance for various mounts"

Wikipedia has a good chart showing the various flange/focal plane distances.

Flange focal distance - Wikipedia, the free encyclopedia

 

[Gavjenks]

Lenses don't have flange to focal distances.
Only cameras have flange to focal distances, which are listed in the chart above.

The various mount options on the back of that lens merely serve to compensate for different flange to focal distances of different cameras, such that the focused image hits the film in every case. There's nothing particularly special about this, other than it comes with them. For almost any lens, though, you can just buy similar adapters to almost any camera that has a shorter flange to focal distance than the camera that lens was designed for.


Edit: awww sniped by derrel.