Canon EF lens mount

Canon EF lens mount

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. The mount is sometimes referredWho|date=September 2008 to as Canon AF which, while not strictly correct, does accurately describe the fact that almost all lenses produced for the mount have full Auto-Focus.Fact|date=September 2008


When 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.

The EF series includes over sixty lenses. The EF series has encompassed focal lengths from 14 to 1200 mm. Many EF lenses include such features as Canon's ultrasonic motor (USM) drive, an image stabilization system (IS), diffractive optics (DO) and, particularly for L-series lenses, fluorite and aspherical lens elements.


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 mmW.J. Markerink maintains an excellent article on "Camera Mounts & Registers" which gives much more detail about flange focal distances and lens compatibility.] . 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. It 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 optical quality.

Third-party lenses

Third-party lenses compatible with EOS electronics are manufactured by Sigma, Tamron, Tokina, and 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. [cite web
url =
author = NK Guy
date = 2007-01-06
work = Canon EOS Beginners’ FAQ
title = Part III - Lenses
] 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

Canon 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 switches.

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 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 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.

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. Lenses that have an image stabilizer, but do not feature this switch, are permanently in Mode 1, therefore when using the image stabilizer, they should not be used for panning.

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

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.

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 camera body.

Related technologies

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 drive

Ultrasonic motor (USM) lenses appeared with the introduction of the EF 300 mm f/2.8L USM lens in 1987. Canon was the first camera maker to successfully commercialise 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.

Some 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.

Image stabilizer

A photograph can easily be ruined when handshake or vibration is introduced during long exposure shots. The Image Stabilizer (IS) counters such problems by optically correcting such shakes with accelerometers and lens groups that move in relation to the shakes, thus minimising or even eliminating minute vibrations from the image.

A general rule-of-thumb to overcome such vibrations would be to set the shutter speed equal to or faster than the reciprocal of the lens' focal length (e.g. 1/60s for a 50 mm lens). IS lenses can improve on this rule by up to four stops. That is, the same 50 mm lens could be used at 1/4s.

Canon has released several versions of the IS system. The original, first used in 1995's 75–300 mm f/4–5.6 IS USM, takes approximately one second to stabilize, provides approximately two stops of stability, is not suitable for use on a tripod (if it cannot detect any motion, it may introduce unwanted motion of its own), and should not be used while panning. The next advance was released with the 300mm f/4L IS USM in 1997 and adds IS mode 2, which is for panning. Mode 2 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 IS USM through 600mm f/4L IS USM), tripod detection was added, so that the lens could be used on a tripod with IS enabled. In 2001, a new version of the Image Stabilizer was created for the 70–200 mm f/2.8L IS USM. Startup time was reduced to approximately 0.5s and the amount of stabilization increased 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. [ [ Canon Camera Museum | Camera Hall - Lenses (EF mount] ] The latest version of Image Stabilizer, released with the EF 200mm f/2L IS USM, allows up to five stops of stabilization. [ [ Canon Camera Museum | Technology Hall] ]

All IS lenses have the words "Image Stabilizer" written on the lens. On some of Canon's larger telephoto lenses incorporating IS, the words "Image Stabilizer" are etched onto a metal plate affixed to the lens.

Diffractive optics

Diffractive optics (DO) are used in lens designs that would otherwise require large and heavy chunks of glass. DO lenses, compared to non-DO lenses of similar focal length and aperture values, are usually smaller and lighter. In addition, DO lenses have superior chromatic aberration suppression characteristics that allow for sharper photographs; the chromatic aberration produced by DO lenses is opposite in direction to that produced by refractive lenses, and so the coupling of a diffractive element and a refractive element can effectively cancel chromatic aberration.

Nevertheless, DO elements are extremely expensive to make due to their high rejection rate, and therefore are introduced in limited EF lenses. Currently 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 are identified with a green ring on the lens barrel.

L-series lenses

Top-of-the-line Canon EF lenses are designated as L-series, or "Luxury" lenses. [cite web
url =
title = EF Lens System
author = Canon
accessdate = 2008-08-01
] L-series lenses have good optical performance and are typically built with a solid construction to withstand constant use and harsh conditions. They can be recognized by a red ring around the front part of the lens. Most recent L lenses have sealing to help resist dust and water. L-series lenses are frequently used by professionals and serious amateurs due to their high optical quality and tough build.

An EF lens is designated as an L-series lens only when it contains at least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass and ground aspherical elements. There are also some lenses which include one or more of these technologies yet which are not designated as L lenses. L-series lenses are also usually equipped with USM (particularly in recent years), IS, or both, but what sets an L-lens apart from the rest is its larger maximum aperture and its build quality. There are also several EF-S lenses which have similar or even better optical performance than Canon L-lenses, however due to the large number of professionals who use full-frame format Canon cameras (and the lack of 'L' quality build on the EF-S range), it is unlikely EF-S lenses will be labeled professional L-series lenses in the near future. There are also some non-L lenses that outperform the L series lenses. [cite web
url =
title = Performance Review of the Canon EF 50mm f/1.0L USM Lens
first = William L. | last = Castleman
date = 2006-02-26
] This is not surprising, as it is much easier to build an excellent lens with a slower aperture.

Larger sized L-series lenses, such as the 70–200 mm and 100–400 mm zooms and longer focal length primes (300 mm+), usually have an off-white barrel (sometimes referred to as the color "putty") to reduce heat absorption under the sun that may otherwise affect the performance of the lens, as well as to identify Canon's lenses, for example at sporting events. However, shorter focal length L-series lenses can be black (such as the Canon EF 24–70 mm f/2.8L and all L-lens primes under 200 mm. Therefore L-series lenses can be identified by either a lens barrel's off-white color or, as on all L-lenses, the distinctive red ring on the lens barrel.

Unlike non-L lenses, Canon's L lenses all ship with the appropriate lens hood and lens pouch in the box. For Canon's non-L lenses, the lens hoods and lens pouches are sold separately. This has come to a criticism for some users, because most other lensmakers supply a hood with every one of their lenses at no additional price.

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 [ Singapore] ).

List of EF lenses

The following is a list of EF lenses made by Canon.Please 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



† – Compact 1:2


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.

ee also

*Canon FD
*Canon EF-S lens mount



* Markerink, Willem-Jan. " [ Camera Mounts & Registers] ". Retrieved on November 6, 2005.

External links

* [ Detailed website with professional and comprehensive reviews of almost all Canon lenses, bodies and speedlite]
* [ A guided tour through the inner workings of an EF lens]
* [ Canon EOS System Explained]
* [ Home of the Canon EF Lens]
* [ EF/EF-S lens chart]
* [ Canon Camera Museum]
* [ List of Canon lenses + informations]
* [ Manual lenses with EOS cameras]
* [ Using Manual Focus Lenses on EOS Bodies]
* [ Professional reviews of lenses]
* [ A scientific tests of lenses, polish language]
* [ A collection of lens resolution tests.]

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