The Canon Magazine 67
EOS S.O.S
Know your Canon
lens mounts
With four different lens mounts you need to make sure you get the right lens
Ask Brian!
Confused with
your Canon DSLR?
Email EOSSOS@
futurenet.comanon’s EOS system launched in
1987 with the introduction of the
EF lens mount. EF (electro focus)swapped mechanical links for a series of
electrical contacts to transfer info between
camera and lens. EF lenses ushered in a
new era of fast accurate AF. EF lenses and
mounts have a red circle to ensure you can
align the lens and body. Macro and tilt-shift
lenses without AF, use the designations
MP-E and TS-E, but fit EF mount cameras.
With the advent of DSLRs and smaller
APS-C size sensors there was a need for
shorter focal length standard zoom lenses.
But to reduce lens size and weight it was
necessary for the rear element to be
situated further in to the body, closer to the
sensor. Canon introduced EF-S mount to
achieve this. EF-S lenses have a smaller
image circle to fit APS-C sensors, but the
mechanics of the mount are the same as
the EF mount. EF-S lenses and mounts
include a white square index mark.
APS-C cameras, except the EOS D30,
D60 and EOS 10D, work with EF-S and EF
lenses, so the mount includes both the red
circle index mark and the white square. The
rear element of EF-S lenses locates further
in to the mirror box, so they do not fit on
full-frame DSLR cameras. While Canon’s
EOS M series mirrorless cameras with
APS-C sensors introduced the EF-M mount.
Moving the lens closer to the sensor, the
EF-M enables smaller, lighter, lenses. EF
and EF-S lenses can be used with the
EF-EOS M mount adapter.
The full-frame EOS R series cameras
have the new RF mount. Canon’s engineers
added faster communication between
camera and lens, and increased mount
diameter. This allows designers to create
lenses that aren’t possible with the EF
mount. The EF-EOS R mount adapter lets
any EF or EF-S series lens be used on the
EOS R bodies. When EF-S lenses are fitted
the R cameras automatically use a smaller
cropped area of the sensor corresponding
to APS-C. This means when you upgrade
from APS-C DSLR to full-frame mirrorless
your EF-S lenses can still be used. However,
there’s no upgrade path that allows EF-M
lenses to be used with EOS R bodies.Canon EF-S lenses can be fitted to
EOS R cameras using the EF-EOS R
mount adapter – the camera then
automatically selects cropped modeC
EF
RF
EF-S/EF
EF-M