A Guide to the Canon EF Lens Mount

In 1987 Canon released the EOS EF mount and conquered the camera market.

Between 1987 and 2018 Canon released 162 EF lenses. A handful of lenses and a cameras are still being sold. (Canon 5D mark IV, Canon Rebel T7)

It’s the best selling camera mount of all time, with Canon selling more than 140 million EF lenses. There’s also an incredible variety of lenses produced by third party manufacturers.

The RF-mount, for mirrorless cameras, has replaced the EF-mount. Canon does not allow third party manufacturers to make full frame autofocus lenses for the RF-mount.

Canon EF DSLRs

APS-H sensors are 27.90mm x 18.60mm with a 1.3 crop factor. That’s larger than an APS-C sensor, but smaller than full frame.

Canon EF 35mm Cameras

Canon Camera Museum EOS Film Cameras.

EF Lenses

They are the most common lenses and offer incredible price to performance.

The last lenses and cameras where released in 2018. After that the focus has been on the RF-mount, for mirrorless cameras.

There are 192 EF lenses, 20 EF-S lenses, and 8 EF-M lenses. The Canon Canon Museum EF lens wing lists all the lenses, with specs and background information.

EF-S and EF-M lenses can not be used on full frame EF mount cameras.

EF lenses can be used on newer RF cameras with a lens adapter.

Lens Acronyms

Image stabilization is the feature to look for.

If you’re planning on shooting video, gets lenses that have an STM motor. They are quieter, so focusing noises won’t be as loud.

• EF - “Electro-focus.” Auto focus. Canon’s answer to the first commercially successful autofocus system, the Minolta A-mount, released in 1985.
• EF-S - Designed for APS-C cameras. The lens will have a white square for aligning mounting.
• EF-M - Lenses were designed for now discontinued APS-C mirrorless cameras.
• EOS - “Electro-Optical System.” All of the connections between the lens and camera are electronic.
• IS - Image stabilization. This is helpful for reducing the effects of camera shake, producing sharper images.
• IF - Internal Focus. The lens will not extend or retract when focusing.
• L - Luxury. They have a red ring around the front of the lens. These are the highest quality lenses, designed for professional use.
• USM - The lens has an UltraSonic Motor.
• STM - The lens has a stepper motor, which is quieter than an USM lens. Better for video.
• I, II, or III - Signifies the generation of the lens.

EF vs EF-S Lenses

Cameras with EF lens mounts cannot use EF-S lenses. The lenses will not be able to be mounted.

On the other hand, cameras with EF-S lens mounts can use EF lenses.

That’s because EF-S cameras have smaller, APS-C sized sensors. The image circle on EF-S lenses will not cover the sensor or film frame.

This wasn’t a problem for Nikon or Sony. Those cameras will go into “crop mode”, which will use a smaller portion of the image sensor. The downside is that resolution will be greatly reduced.

Adapting Lenses

The Canon EF mount has a flange focal distance of 44mm.

That is larger than the 42mm for the Canon FD mount. There is no room for an adapter. The lens would be too far away from the film or sensor plane.

It would be the same as if an extension tube was used for macro photography. The lens would lose the ability to focus on distances starting with infinity.

There are adapters that allow M42 screw mount lenses to be used. Get one with electronic contacts. The ‘dandelion’ chip is needed for focus confirmation to work.

EF lenses can easily be adapted to Canon RF and mirrorless cameras from other manufacturers. Not needing a flappy mirror frees up a couple centimeters of space, which is perfect for an adapter.