A Refresher: The Canon Mount Adapter EF-EOS M

February 14, 2017

With the recent addition of two compact, interchangeable lens cameras in Canon’s M-series line — the EOS M5, and in early 2017, the EOS M6 — it’s probably appropriate to take a new look at Canon’s optional, accessory Mount Adapter EF-EOS M.  This lens mount adapter has been with us since the dawn of the EOS M-series of cameras, beginning in 2012.

This accessory is the key to expanding the versatility of any EOS M-series camera model, allowing lenses for conventional EOS digital SLRs to be mounted on these very compact cameras.  In this article, we’ll take a look at the practical matter of using this lens mount adapter, and provide a brief technical refresher for readers who may be interested in more than the basics.

Quick review:  the EOS M-series cameras

Canon continues to market a wide range of EOS digital SLRs, from EOS Rebel models to the top-of-the-line EOS-1D X Mark II (as of early 2017), targeting an enormous range of prospective customers from casual amateur users to full-time working professional photographers.  But along with other camera makers, Canon has introduced a new, more compact alternative — which still offers the flexibility of interchangeable lenses.  This is Canon’s EOS M series of cameras.  A number of models have been introduced since the first EOS M camera of 2012.  These cameras share some basic features:

  • First and foremost, a very compact size and form-factor
  • Lens interchangeability — using a new, smaller “EF-M” lens mount, and with their so-called “mirrorless” structure, a much shorter lens mount-to-image sensor distance than is used in traditional Canon EOS digital SLRs
  • The same (relatively) large, APS-C size imaging sensors used in Canon entry-level and mid-range DSLRs, such as the EOS 80D and EOS 7D Mark II
  • AF performed exclusively off the imaging sensor, meaning all still-image shooting is similar to Live View in recent EOS digital SLRs (unlike EOS DSLRs, there’s no separate AF sensor)
  • A primary series of very compact, dedicated lenses, called EF-M lenses — these can be mounted directly to any EOS M-series camera, and do not require any adapter to mount and use (for stills and for video)
  • Compatibility with traditional lenses for Canon EOS digital SLRs, by using the optional Canon Mount Adapter EF–EOS M.
There have been a number of Canon EOS M-series cameras, all with a much more compact design than traditional digital SLRs, but opening the door to lens interchangeability — a key differentiator when compared to traditional, fixed-lens pocket cameras, and of course when compared to smartphones. Canon’s EOS M6 is pictured here.

The Canon Mount Adapter EF–EOS M

This durable adapter mounts directly onto any EOS M-series camera model, using the camera’s EF-M lens mount.  On the front surface of the Mount Adapter is a larger Canon EF/EF-S mount, to accept lenses from traditional Canon EOS digital SLRs.

One cool feature is the built-in tripod adapter, which is removable at any time with a convenient thumb screw.  There are a couple of important notes about this tripod adapter for the Mount Adapter EF-EOS M:

  • If using the Mount Adapter EF-EOS M, along with a tripod, do not attach the tripod to the camera’s tripod socket —use the tripod mount on the Mount Adapter, assuming the EF/EF-S lens you’re attaching does not have its own tripod mount.
  • For lenses which incorporate their own tripod mount (larger lenses like the EF 70-200mm L-series lenses, and so on), continue to attach to a tripod using the lens’ tripod mount, rather than the tripod adapter on the Lens Mount Adapter EF-EOS M.  Never use the camera body’s tripod socket in these situations!

Canon engineers strongly suggest mounting an EF or EF-S lens to the front of the accessory Mount Adapter EF-EOS M, and then mounting the combination of lens + adapter to the camera body.  Similarly, remove the combination from the camera when you’re finished using it, and detach the lens from the Mount Adapter with both off the camera.  And, for EOS M-series cameras, it is recommended to turn the camera’s main on-off switch to the OFF position, before mounting or dismounting the lens + adapter combination.

What lenses are compatible with the Mount Adapter EF–EOS M?

Basically, any of the following can be mounted onto any EOS M-series camera body (as of early 2017), using the optional Canon Mount Adapter EF–EOS M:

  • Canon EF lenses (all)
  • Canon EF-S lenses (all)
  • Canon TS-E (tilt-shift) lenses — all
  • Canon MP-E 65mm 1~5x macrophoto lens

Please note that Canon’s CN-E (Cinema EOS) and EF-M lenses are not supported with this adapter!

AF and other lens operations, with the Mount Adapter EF–EOS M

The Mount Adapter has electronic contacts to allow communication between compatible lenses and EOS M-series cameras, so most functions continue to work as expected.  In particular, AF with EF and EF-S lenses will function, using the same camera features offered by the EOS-M camera model in question.

With early EOS M-series models, if the camera was set to Servo continuous AF, the lens would focus for the first shot in a sequence, and AF would then be locked at that position, from the second frame onward.  This is no longer the case with cameras such as the recent EOS M5 and M6 models.

Minimum focus distance is essentially unchanged when the mount adapter is used with traditional EOS lenses for DSLRs.  Infinity focus is always possible, and a lens’ minimum focus usually remains the same as it would on a traditional digital SLR.  In some instances, for technical reasons, a lens’ closest focus distance may be slightly longer, when attached to the Mount Adapter.  However, no user compensation is needed… what you see on the camera’s LCD monitor or eye-level viewfinder represents what the imaging sensor is seeing.

Exposure control remains exactly the same when using an EF/EF-S lens and the Mount Adapter, too.  No compensation is required, and there’s no light loss.

Technical stuff

All Canon EOS digital SLRs to date (and all previous 35mm film-based EOS SLRs) have maintained a constant distance from lens mount reference point to image sensor/film plane of 44.00mm.  By removing the entire mirror box and mechanism, however, so-called “mirrorless” cameras can have the distance from rear of lens to image sensor reduced greatly — resulting in a much more compact camera body.

In Canon’s M-series cameras, the distance is reduced to less than half that of EOS DSLRs — only 18mm from mount to image sensor.

A key difference in cameras with a mirrorless structure is that they can have a much shorter distance from lens to image sensor. As shown here, Canon’s EOS M-series cameras have a distance of only 18mm, less than half of that required for traditional EOS DSLRs, resulting in a significantly slimmer camera body. But, this means that lenses mounted directly (EF-M lenses) have to be designed strictly for EOS-M cameras. The optional Canon Mount Adapter EF–EOS M positions an EF/EF-S lens precisely 44mm from the image sensor, maintaining the same optical and exposure integrity designed into traditional DSLR lenses.

By adding the available Canon Mount Adapter EF-EOS M, any attached lens is restored to the 44mm mount-to-sensor distance it was originally designed for.  Since this distance remains the same, there’s no loss of infinity focus when an EF or EF-S lens is attached (there are no optics in the mount adapter), nor is there any loss of light or changes in exposure control.  All exposure modes remain completely available.


The primary point is that for any current Canon EOS digital SLR photographer, the option to add a very compact yet interchangeable lens camera is a realistic possibility.  The EOS M-series cameras are a compelling choice when size — with flexibility — is a priority.  This can be for travel, or any other photographic purpose.

With the simple addition of the optional Canon Mount Adapter EF-EOS M, any of the lenses you now own for any EOS D-SLR can continue to be utilized on an EOS M-series camera.  Macro lenses, wide-angle lenses, wide-aperture “normal” lenses, even telephotos… all the optical possibilities you’ve experienced on an EOS digital SLR transition nearly seamlessly to any Canon EOS M-series camera you may choose to invest in.  It’s yet another reason to consider adding an EOS M5, M6, or M10 to your photographic arsenal.

The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.


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