Eos Ef Usm?

[Ryguyinlj]

I am curious, what do EF, EF-S, and USM stand for?

Thanks.

[Trevor Ash]

I am curious, what do EF, EF-S, and USM stand for?

Thanks.

These are all terms for Canon products.

EF = Electronic Focus. It is the name for the type of "mount" used on the lenses and camera.
EF-S = I have no idea with the "S" stands for but it's referring to a newer type of lens mount that can be found on the EOS 20D and Digital Rebel camera. In a nutshell, this mount allows for wider angle lenses.

USM = Ultrasonic Motors. It's a kind of motor that Canon puts into some of it's lenses. The motor is used for focusing. Typically, USM is quieter and quicker than non-USM but this may not always be the case.

[mjs1973]

I believe that the S in EF-S stands for short. The back part of the lens is shorter than the typical EF lens and is designed to work with a specific camera body. For example: the EF-S 18-55 lens that comes with the DRebel kit only works with the DRebel.

[SmartWombat]

EF is the Canon lens mount in use today, older FD lenses don't fit an EF mount camera.

EF-S is for short backfocus lenses.
That's where the rearmost element of the lens protrudes into the camera body, and would be hit by the mirror of an EF camera. EF-S is only found (today) on the digital cameras.
It's used by the 10-22mm lens which fits the 20D and 10D - but not the 1D.

USM is the focussing motor, UltraSonic Motor , used in the lens. It's allegedly faster and quieter focussing than other lenses - but al my lenses are USM so I can't compare.

[straightarm]

10-22mm
18-55mm
17-85mm IS

The current cameras that take EF-S lenses are the EOS 20D and the 300D/DRebel

The 10D does not take the EF-S lenses, although some people did modify the 18-55 lens so it would fit the 10D

The incorporation of the EF-S mount was one of the significant changes between the 10D & 20D