Gene Wright Talks About the 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.

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 EF-S lenses.

History

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.

Versatility

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. 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

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 camera body.

Related technologies

Ultrasonic motor drive

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.

Image stabilizer

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 panning. 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.

Diffractive optics

L-series lenses

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 Singapore).

Communication protocol

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

EF Zoom Lenses

Focal length	Aperture	USM	IS	L-series	DO
16–35 mm I	f/2.8	Yes	No	Yes	No
16–35 mm II	f/2.8	Yes	No	Yes	No
17–35 mm	f/2.8	Yes	No	Yes	No
17–40 mm	f/4	Yes	No	Yes	No
20–35 mm	f/2.8	No	No	Yes	No
20–35 mm	f/3.5–4.5	Yes	No	No	No
22–55 mm	f/4-5.6	Yes	No	No	No
24-70 mm	f/2.8	Yes	No	Yes	No
24-85 mm	f/3.5-4.5	Yes	No	No	No
24-105 mm	f/4	Yes	Yes	Yes	No
28-70 mm	f/2.8	Yes	No	Yes	No
28-70 mm II	f/3.5-4.5	No	No	No	No
28-80 mm	f/2.8-4	Yes	No	Yes	No
28-80 mm II	f/3.5-5.6	No	No	No	No
28-80 mm II	f/3.5-5.6	Yes	No	No	No
28-80 mm V	f/3.5-5.6	Yes	No	No	No
28-90 mm II	f/4-5.6	Yes	No	No	No
28-90 mm III	f/4-5.6	No	No	No	No
28-105 mm	f/3.5-4.5	Yes	No	No	No
28-105 mm II	f/3.5-4.5	Yes	No	No	No
28-105 mm	f/4-5.6	Yes	No	No	No
28-135 mm	f/3.5-5.6	Yes	Yes	No	No
28-200 mm	f/3.5-5.6	Yes	No	No	No
28-200 mm	f/3.5-5.6	No	No	No	No
28-300 mm	f/3.5-5.6	Yes	Yes	Yes	No
35-70 mm	f/3.5-4.5	No	No	No	No
35-70 mm	f/3.5-4.5A	No	No	No	No
35-80 mm III	f/4-5.6	No	No	No	No
35-80 mm	f/4-5.6	Yes	No	No	No
35-105 mm	f/3.5-4.5	No	No	No	No
35-105 mm	f/4.5-5.6	No	No	No	No
35-135 mm	f/3.5-4.5	No	No	No	No
35-135 mm	f/4-5.6	Yes	No	No	No
35-350 mm	f/3.5-5.6	Yes	No	Yes	No
38-76 mm	f/4.5-5.6	No	No	No	No
50-200 mm	f/3.5-4.5	No	No	No	No
50-200 mm	f/3.5-4.5	No	No	Yes	No
55-200 mm II	f/4.5-5.6	Yes	No	No	No
70-200 mm	f/2.8	Yes	Yes	Yes	No
70-200 mm	f/2.8	Yes	No	Yes	No
70-200 mm	f/4	Yes	Yes	Yes	No
70-200 mm	f/4	Yes	No	Yes	No
70-210 mm	f/3.5-4.5	Yes	No	No	No
70-210 mm	f/4	No	No	No	No
70-300 mm	f/4.5-5.6	Yes	Yes	No	Yes
70-300 mm	f/4-5.6	Yes	Yes	No	No
75-300 mm	f/4-5.6	Yes	Yes	No	No
75-300 mm III	f/4-5.6	Yes	No	No	No
75-300 mm III	f/4-5.6	No	No	No	No
80-200 mm	f/2.8	No	No	Yes	No
80-200 mm	f/4.5-5.6	Yes	No	No	No
80-200 mm II	f/4.5-5.6	No	No	No	No
90-300 mm	f/4.5-5.6	No	No	No	No
90-300 mm	f/4.5-5.6	Yes	No	No	No
100-200 mm	f/4.5A	No	No	No	No
100-300 mm	f/4.5-5.6	Yes	No	No	No
100-300 mm	f/5.6	No	No	No	No
100-300 mm	f/5.6	No	No	Yes	No
100-400 mm	f/4.5-5.6	Yes	Yes	Yes	No

EF Prime Lenses

Focal length	Aperture	Macro	USM	IS	L-series	DO
14 mm	f/2.8	No	Yes	No	Yes	No
14mm II	f/2.8	No	Yes	No	Yes	No
15 mm (fisheye)	f/2.8	No	No	No	No	No
20 mm	f/2.8	No	Yes	No	No	No
24 mm	f/1.4	No	Yes	No	Yes	No
24 mm II	f/1.4	No	Yes	No	Yes	No
24 mm	f/2.8	No	No	No	No	No
28 mm	f/1.8	No	Yes	No	No	No
28 mm	f/2.8	No	No	No	No	No
35 mm	f/1.4	No	Yes	No	Yes	No
35 mm	f/2	No	No	No	No	No
50 mm	f/1.0	No	Yes	No	Yes	No
50 mm	f/1.2	No	Yes	No	Yes	No
50 mm	f/1.4	No	Yes	No	No	No
50 mm II	f/1.8	No	No	No	No	No
50 mm	f/2.5	Yes †	No	No	No	No
85 mm	f/1.2	No	Yes	No	Yes	No
85 mm II	f/1.2	No	Yes	No	Yes	No
85 mm	f/1.8	No	Yes	No	No	No
100 mm	f/2	No	Yes	No	No	No
100 mm	f/2.8	Yes	No	No	No	No
100 mm	f/2.8	Yes	Yes	No	No	No
135 mm	f/2	No	Yes	No	Yes	No
135 mm (SoftFocus)	f/2.8	No	No	No	No	No
180 mm	f/3.5	Yes	Yes	No	Yes	No
200 mm	f/1.8	No	Yes	No	Yes	No
200 mm	f/2.0	No	Yes	Yes	Yes	No
200 mm II	f/2.8	No	Yes	No	Yes	No
300 mm	f/2.8	No	Yes	No	Yes	No
300 mm	f/2.8	No	Yes	Yes	Yes	No
300 mm	f/4	No	Yes	No	Yes	No
300 mm	f/4	No	Yes	Yes	Yes	No
400 mm II	f/2.8	No	Yes	No	Yes	No
400 mm	f/2.8	No	Yes	Yes	Yes	No
400 mm	f/4	No	Yes	Yes	No	Yes
400 mm	f/5.6	No	Yes	No	Yes	No
500 mm	f/4	No	Yes	Yes	Yes	No
500 mm	f/4.5	No	Yes	No	Yes	No
600 mm	f/4	No	Yes	No	Yes	No
600 mm	f/4	No	Yes	Yes	Yes	No
800 mm	f/5.6	No	Yes	Yes	Yes	No
1200 mm	f/5.6	No	Yes	No	Yes	No

† – Compact 1:2

Exceptions

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 confirmation.