The EF lens mount allows all the Canon EF lenses to be used on any of the
Canon EOS line of cameras made by Canon Inc.
Unlike the EF's breech-lock predecessor, the FD mount, the EF mount uses a bayonet-style mount. EF stands for "Electro-Focus":
automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens. All communication between camera
and lens takes place through electrical contacts; there are no mechanical levers or plungers.
In 2003, Canon introduced the EF-S lens mount, a derivative of the EF mount that is strictly
for digital EOS cameras with a 1.6x crop released after 2003. All other EOS cameras that only have an EF mount will not mount
The EF mount of a Canon EOS 50When the EF mount was introduced in 1987, it had the largest mount diameter (54 mm internal)
among all 35 mm SLR cameras, allowing
large aperture lenses to be designed for the EOS system
Unlike the standard autofocus lens mounting technology of the time, which used a motor in the
camera body to drive the mechanics of the focus helicoid in the lens by using a transfer gear, the EF series used a motor
inside the lens itself for focusing. This allowed for autofocusing lenses which did not require mechanical contacts in the
mount mechanism, only electrical ones to supply power and instructions to the lens motor. The motors were designed for the
particular lens they were installed in.
Although Canon does not endorse (and in fact warns against) the use of third-party lenses and
adapters, the EF lens mount works with adapters due to its large diameter and the relatively short flange focal distance of
44.0 mm. It is possible to mount lenses using the
Nikon F mount, Olympus OM, Leica R and universal M42 lens mounts (among others) by the use of
a mechanical adapter. The earlier FD mount is not usable for general photography unless adapters with optical elements are
used because its flange focal distance was only 42.0 mm; infinity focus would be lost with an adapter which lacks optical
elements. The Canon FD-EOS adapter is rare and is only usable with certain FD telephoto lenses. With a manual connection,
the aperture and focus controls of the lens cannot be controlled or read from the camera; the lens must be focused manually.
Since the only possible metering is through-the-lens, the lens must be manually stopped down to accurately meter at anything
less than full aperture. (This is called stop-down metering.)
For other lens types, an adapter would act as an extension tube, causing the lens to lose the ability to focus to infinity.
Alternatively, the lens adapters would include optical elements and act as weak teleconverters, as well as possibly losing
Third-party lenses compatible with EOS electronics are manufactured by
Carl Zeiss. The manufacturers of these lenses have reverse engineered the
electronics of the EF lens mount. The use of these lenses is not supported by Canon. Sometimes compatibility problems arise,
as no third party has access to Canon's specifications for camera-body communication. It is not accurate to call these lenses
EF mount, as that term is reserved by Canon for its own lenses exclusively.
Controls and Features
An EF lens showing its different controls and featuresCanon EF lenses typically have a number of controls, switches and
physical features, used by the photographer so they can control the lens. The types and number of the controls can vary from
lens to lens. With the most basic lenses having only a few, to the most complex having over a dozen different controls and
This is a list of the different controls and switches found on most Canon EF lenses, along with a detailed description on
what they are used for.
Lens mount index: This marking is found on all EF lenses. It is used for matching the EF lens mount to the mount on an
EOS body, so one can connect the lens to the body quickly. On EF lenses, this can be identified as a round red mark, while on
EF-S lenses, this will be a square white mark.
Focusing ring: This control is found on most EF lenses. It is used for focusing the lens, so the subject that one
wishes to photograph is in focus. This control is usually a ring on the lens body, that can be turned. On some lenses, such
as the Canon EF-S 18-55mm lens, this is simply the inner lens barrel.
Zoom ring: This control is found on EF zoom lenses. It is used for changing the focal length of the lens. The zoom
ring usually has certain, common, focal lengths marked on it. To set the zoom ring to any given focal length, one must turn
the ring so that the marked focal length matches the zoom index. The zoom index is typically a white, or black, line found
next to the zoom ring.
Distance scale of an EF lens.Distance scale window: This feature is found on most EF lenses. This feature, while not a
control or switch, is useful to the photographer for determining, or setting, the lens's focus distance. It is used in
conjunction with the Focusing ring, when rotated, the distance scale will also rotate to show the changing focus distance.
On some lenses the distance scale also has an infrared index. These are shown as red markings below the distance scale. This
is used for making focus adjustments when the photographer is doing infrared photography. To make an adjustment, first focus
the subject, then turn the Focusing ring so it matches the corresponding infrared index mark.
Focus mode, and focusing range switches.Focus mode switch: This switch is found on most EF lenses that have an
autofocus feature. It is used for setting the lens to either autofocus mode, or manual focus. When set to auto-focus mode
(AF), the lens will autofocus when commanded by the camera. When set to manual focus (MF) the photographer must focus the
lens by using the Focusing ring.
Focusing distance range limiter switch: This switch is found on most longer focal length lenses, and macro lenses. It
is used for limiting the focusing distance range of the lens, when using it in autofocus mode. Most lenses have two settings,
these are usually full focus range (from minimum focus distance to infinity), and distant focus range (from half way point of
focus range to infinity). Other lenses have three settings, with the additional setting usually being near focus range (from
minimum focus distance to half way point of focus range). The reason for this feature is to shorten the autofocus time for
the lens. Longer focal length lenses, and macro lenses, have a longer travel distance for the focusing mechanic inside the
lens. So when the photographer knows they will not need a certain part of the focus distance range, limiting it will help
shorten the autofocus time, and possibly prevent "focus hunting".
Soft Focus Ring: This ring is found only on the 135mm 'Soft Focus' prime lens, and enables a variable soft focus
effect from completely sharp (0) to very soft (2), although it has little effect when used with apertures over f/5.6.
Although variable two 'stops' are implemented at positions 1 and 2.
Both types of image stabilizer switches.Image stabilizer switch: This switch is found on all EF lenses that feature an image
stabilizer. It is used for turning the image stablizer "on"( | ), or "off"( o ).
Image stabilizer mode switch: This switch is found on most EF lenses that feature an image stabilizer. The switch has
two settings Mode 1, and Mode 2. Mode 1 is normal mode, used for typical photography, where the subject does not move. Mode 2
is used for panning, this is useful for sports or wildlife photography, where the subject moves constantly and one will need
to pan. One should not use Mode 1 for panning as this will typically cause blurred photographs. Most older lenses that have
an image stabilizer, but do not feature this switch, are permanently in Mode 1. However newer lenses, such as the Canon EF-S
18-200mm lens, are able to detect if they are being panned in either axis and will auto disable the stabilization for the
axis parallel to movement. Therefore they do not need this switch.
Autofocus stop buttons: These buttons are found on super telephoto EF lenses, evenly spaced around the front collar
of the lens. They are used for temporarily stopping the autofocus feature of the lens. Only one button needs to be pressed
to activate the feature. To use this button, one must first have the autofocus active, then when one wishes to halt autofocus,
they will press and hold the button. When they wish to resume autofocus, they will release the button.
Focus preset: The focus preset feature is found on most super telephoto EF lenses. The focus preset feature uses 1
switch, 1 button, and 1 ring. It is used for presetting a given focus distance into memory, so that the photographer can
quickly recall the focus distance, without the need for autofocus. The switch has three settings "off"( o ), "on"( | ), or
"on with sound"( ((- ), and is used for turning on the feature, and deciding if sound is desired. The "set" button is used
for saving the focus distance into memory. The focus preset ring is used for recalling the memory save point, it is a thin
knurled ring, usually located in front of the Focusing ring. To use this feature, one must set the switch to either "on", or
"on with sound", then the photographer will focus the lens to the point they wish to save at, then press the "set" button.
After this, when the feature is turned on, the photographer can turn the focus preset ring, and the lens will recall and
focus quickly to the save point that was set. This feature is useful for sports and birding photography
Rear gel filter holder on an EF lens.Filter mounting: This mount is used for attaching filters to EF lenses. There
are three types, front threaded mount, inner drop-in mount, and rear gelatin holders. Front threaded filters are used on
most lenses, and are attached by threading, and tightening the filter. Inner, drop-in filter mounts are used on super
telephoto EF lenses. They are attached by first pressing the two "opposing" buttons on the filter mount, and pulling it out.
Then either a 52mm round threaded filter is attached, or one can use a gelatin filter. Rear gelatin filter holders are used
by cutting out a sheet of gelatin, to the size shown on the back of the lens, then it is slid in the holder. Filter mounts
are useful for all types of photography, every EF lens has either one, or on some lenses two, of the three types used.
Lens hood mount: This feature is found on most EF lenses. This mount is used for attaching the lens hood. The hood
mount is of a bayonet style on most EF lenses, though a clip-on style hood mount is used for a small selection of current
lenses (85mm f/1.2L USM,
85mm f/1.8 USM and 100mm f/2 USM)
Tripod collar: This feature is found on most longer focal length lenses, and macro lenses. The tripod collar is used
for attaching the tripod ring. There are two main styles of tripod rings. One type is opened up, placed on the lenses tripod
collar, then closed and tightened. The other type, does not open, but instead is slid up the lens from the mount end, and
tightened. To set the tripod ring so that it is level with the lens, rotate the ring until the index mark on the tripod
ring matches the index mark on the distance scale. The tripod ring is used for attaching to a tripod/monopod, instead of the
With the release of the EOS 300D Canon introduced a variation on the standard EF lens mount called EF-S. The "S" stands for
"Short Back Focus". These lenses are designed for and may only be used with cameras featuring a 1.6x FOV APS-C size sensor.
Ultrasonic motor (USM) lenses appeared with the introduction of the EF 300mm f/2.8L USM lens in 1987. Canon was the first
camera maker to successfully commercialize the USM technology. EF lenses equipped with USM drives have fast, silent and
precise autofocus operations, and consume less power compared to other AF drive motors.
There are two types of USMs, the ring-type USM and the micromotor USM. Ring-type USM allows for full-time manual focus
operations without switching out of AF mode. Micromotor USM is used to bring down the cost of the lens. It is possible to
implement full-time manual focus even with micromotor USM; however, it requires additional mechanical components.
Ultrasonic logoSome USM lenses are identified with a gold ring and the label "Ultrasonic" printed in gold on the lens barrel.
All L lenses which have USM do not have the gold ring, but the red ring which denotes them as an L lens. However, they have
the label "Ultrasonic" printed in red on the lens barrel.
The image-stabilized Canon EF 300mm f/4L IS USM lens
The image stabilization technology detects handheld motion and optically
corrects it. It only corrects handheld motion; if the subject of the photograph is moving, IS will not stop it. It also can
only stabilize so much motion, ranging from two to five stops of light. Canon has released several versions of the IS system.
The first version, first used in the 75-300mm lens (1995), takes approximately
one second to stabilize, provides approximately two stops of stability, is not suitable for use on a tripod and or for
The 300mm f/4L IS USM lens, released in 1997, adds IS Mode 2, which detects whether panning is taking place horizontally or
vertically, and only compensates for vibration in the plane perpendicular to the plane of panning.
In 1999, with the release of the IS super-telephoto lenses (300mm f/2.8L through 600mm f/4L), tripod detection was added,
so that the lens could be used on a tripod with IS turned on.
In 2001, a new version of the Image Stabilizer was created for the 70–200mm f/2.8L. This version takes about approximately
0.5s and can be stabilized up to three stops.
In 2006, the 70–200 mm f/4L IS USM was released with an Image Stabilizer which allows up to four stops of stabilization.
The latest version of Image Stabilizer, released with the EF 200mm f/2L IS USM, allows up to five stops of stabilization.
All EF lenses that support IS have the words "Image Stabilizer" written on the lens. On some of Canon's larger telephoto
lenses, the words "Image Stabilizer" are etched onto a metal plate affixed to the lens.
The green-ringed EF 70–300 mm f/4.5–5.6 DO IS USMDiffractive optics (DO) are special kinds of glass that are used in some
lenses. DO lenses, compared to non-DO lenses of similar focal length and aperture values, are usually smaller and lighter
and are better at handling
chromatic aberration. They are more expensive to make than non-DO lenses. Only the EF 400 mm
f/4 DO IS USM and the EF 70–300 mm f/4.5–5.6 DO IS USM contain DO elements. DO lenses have a green ring on the barrel.
The 70–200 mm f/2.8L lens Main article: Canon L lens
Top-of-the-line Canon EF lenses are designated as L-series, or "Luxury" lenses. L-series lenses have good optical performance
and a solid construction. Canon ships all L lenses with a hood and pouch; photographers must purchase the hood and pouch
separately for non-L lenses. Distinctive visual characteristics include a red ring around the lens and an off-white color
on some lenses (to reduce heat absorption). Some L lenses have environmental and weather protection against the other
All L lenses include at least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass
and ground aspherical elements. Other mechanical characteristics of L lenses (but not exclusive to them) are the USM
(particularly in recent years) and Image Stabilization technologies.
Owning a number of L-series lenses along with at least one professional EOS camera body is a requirement for admittance
into the Canon Professional Service in most markets (for example, three for Europe and Australia, one for Hong Kong and
The communication protocol between the camera is 8-bit SPI. The pins, from right to left on the lens, are:
Canon EF mount pins
+6 volts to power internal lens focus motors
Present on all EOS
bodies and lenses
Digital logic power
Data from camera to the lens (MOSI)
Data from the lens to the camera (MISO)
Camera body generated clock signal (SCLK)
Digital logic ground
Only on most L-series and some
Short to COM1 for 'Life Size Converter' and x1.4
Short to COM1 for x2 and x1.4 teleconverter
The information from the lens is used by the camera body for
focusing and metering, and with digital camera bodies
The information from the lens is used by the camera body for focusing and metering, and with digital camera bodies it is
used to record the lens parameters in the EXIF data in the images. All L series primes longer than 135mm, the 70-200 zooms,
100-400 zoom, and the EF 50mm f/2.5 Compact Macro, have an additional three communication pins. These additional pins are
used by the Canon Extender EF adapters and the Life-Size Converter EF to indicate to the lens the change in focal length
so that it is able to report the correct focal length and aperture to the camera body when mounted on a teleconverter.
List of EF lenses
See also: List of Canon EF-S lenses
The following is a list of EF lenses made by Canon. Note that the "I", "II", "III", etc. after the focal length(s)
indicates the latest generation number for that model.
The EF lenses are grouped below by their focal lengths:
Zoom: for zoom lenses that have a range of focal lengths
Prime: for prime lenses that have a single focal length
Canon has two types of lenses, Tilt-shift and
the 1-5x Macro lens, which are not designated EF,
but TS-E and MP-E respectively. TS stands for
Tilt-shift while MP stands for Macro photo.
These types of lenses, while not designated EF,
are still compatible with the EF mount. These
lenses are not designated as EF as they are
manual-focus only lenses, and therefore are not
electro-focus. They do, however, retain
electronic aperture control as well as focus