Lens Mounts: A Reference for Using Adapters

As a long-term experimenter with old lenses on my Canon DSLRs it’s important to know which lens mounts can be adapted to work with the Canon EF system.

The mount to sensor distance on Canon DSLRs is 44mm, so if the mount to film-plane distance for another lens system is greater than this I should be good to go. Adding a whatever to EF mount adapter to the front of my DSLR should push the old lens out to the correct distance from the sensor to work over the full focal range of the lens.

Note that we’re talking here about manual focus lenses with mechanical aperture setting. As far as I’m aware nobody is producing mount adapters to support setting the aperture of a non-native lens electronically from the camera. So if you want to be able to change aperture settings with the lens in place, it has to be mechanical.

The table below lists a selection of the more common (and some of the less common) mounts with their mount to sensor or film plane distances. The top section contains some of the newer mirrorless mounts and the second lists some of the older mechanical and electronic lens mounts. The list is by no means exhaustive, but does contain all of the mounts I’ve had any dealings with in my dabbling with film cameras and older lenses.

Lens Mount to Sensor Distances and Mount Diameters

Lens Mount	Mount/Sensor Distance	Mount Diameter
Pentax Q	9.2mm	31mm
Nikon Z	16.0mm	55mm
Nikon 1	17.0mm	40mm
Fujifilm X	17.7mm	44mm
Canon EF-M	18.0mm	46.5mm
Sony E	18.0mm	46.1mm
Micro Four Thirds	19.25mm	38mm
Canon RF	20.0mm	53.9mm
Leica L	20.0mm	51.6mm
Samsung NX	25.5mm	42mm
Fujifilm G	26.7mm	65mm
Lens Mount	Mount/sensor distance	Diameter
Konica F	40.5mm	40mm
Konica AR	40.5mm	47mm
Canon FL	42.0mm	48mm
Canon FD	42.0mm	48mm
Fujica X	43.5mm	49mm
Minolta SR	43.5mm	44.7mm
Canon EF	44.0mm	53.9mm
Sigma SA	44.0mm	44mm
Practica B	44.4mm	42mm
Rollei QBM	44.5mm	46mm
Sony A (Minolta A)	44.5mm	49.7mm
Exacta	44.7mm	46mm
M39	45.46 mm	39mm
M42	45.46 mm	42mm
Pentax K	45.46 mm	44mm
Contax C/Y	45.5mm	48mm
Mamiya ZE	45.5mm	?
Olympus OM	46.0mm	47.1mm
Nikon F	46.5mm	46.9mm
Leica R	47.0mm	49mm
T mount	55.0mm	42mm

Now that might look like a very boring table, but the way it works is that any lens mount further down the table than the camera you want to attach the lens to should work. The difference between the two mount to sensor (or film plane) distances is the thickness of the mount adapter. If the lens is futher up the table than the camera body it may still be possible to get an adapter, but it will have an optical element in it.

Practical aspects

There is, however, a physical aspect to making lens mounts that makes this not quite true. While theoretically it should be possible to mount a Practica B lens on a Canon EF camera body, the thickness of the adapter will only be 0.4mm (44.4 – 44.0). This may be too thin to actually manufacture with enough strength to work in practice.

Using a Pentax K lens on the same body gives an adapter thickness of 1.46mm (45.46 – 44.0) which is a lot more practical. In fact I’ve used one of these for years, as my first film SLRs used this mount and I still have several of the lenses.

Lenses that won’t work

That’s the theory. Taking a look at old Canon FD mount glass, the shorter lens to film plane distance of 42mm means these won’t work with a Canon EF camera without optical correction in the adapter. Personally, I’ve never been too keen on the idea of using adapters with an optical element, as while Canon’s FD lenses were optically very good, who knows the provenance of the optical element in a third party mount adapter?

As a result, for me as a Canon EF user quite a few of the old lens systems were effectively off limits: Konica AR, Canon FL and FD, Fujica X and Minolta SR lenses probably being the most notable. Over the years as well as Pentax K I’ve used M39, M42 and Olympus OM mount lenses on my Canon DSLRs with great (and sometimes not so great) results.

They may be getting a bit long in the tooth, but I’m still a pretty regular user of M42 lenses like the Helios 44 series. From time to time I also use a couple of anamorfake-converted Pentacon lenses, a 50mm f1.8 and my rebodied 135mm f2.8.

The Wonder of Mirrorless

Having moved to mirrorless this year with the Canon EOS-R, the mount to sensor distance in my camera is now 20mm. As well as being able to use my existing mount collection in conjuction with a Canon EF to RF adapter, suddenly a load of additional old glass should now work with my camera. Canon’s RF is not the shortest mount to sensor distance either, so potentially all the old mount systems should work with any of the other manufacturers’ mirrorless systems as well, as long as somebody’s producing a suitable mount adapter.

One that I plan to get very soon is a Minolta SR (also known as MC or MD) to RF mount. I’ve had a Minolta mount copy of the classic Vivitar Series 1 28-90mm f2.8-3.5 “stovepipe” lens sitting in a cupboard for years waiting for it’s chance to shine. Now might finally be the time!