All about Canon SLR part 3

EOS camera auto focus system

In principle, auto focus (AF) on EOS cameras use the AF motor in the lens, in other words all Canon EF lenses have AF motor in it. This is different to that has motorcycle Nikon AF on the camera body (although not all have a Nikon digital SLR AF motor), in other words not all Nikon lenses have AF motor. However, Canon did not treat each with the same lens, which lens provided cheap and expensive lens AF motors of different types and quality.

There are two types of motors in Canon lenses, namely:

* Motor AFD (arc-form drive) or micromotor drives -> for cheap lenses
* Motor USM (ultrasonic motor) -> for expensive lenses

AFD motor is a conventional micro motor and cheap. It poses a rotating magnetic coil when energized electrical voltage. Motor is quiet noisy when spinning and the speed was mediocre. Note that the lens Canon EF / EF-S is not labeled USM motor in it means taking the AFD system (confused with Nikon AF-S lenses that must have been wearing motorcycle SWM).

USM is a new tekolonogi motor that drives the motor with a wave that provides higher speed but with a more refined sound. But again, dividing the Canon USM lenses with this technology into two groups, namely USM lens for expensive and USM lens for an ordinary lens.

The two types of motor USM in Canon lenses, namely:

* Based USM lens ring for expensive (see example image above)
* Based USM micromotor for a cheaper lens

Differences exist both in the working principles and the ability of instant manual focus (FTM: full-time manual). In ring-based USM lens, we can simply turn the manual focus ring anytime we want. So switching from auto focus to manual focus can be done directly without moving the lever AF to MF. When using a non USM lens or lens cheap USM (with micromotor), we have to move the lever just play AF to MF manual focus ring.

Lens with USM or not the code will not affect the optical quality, because only signifies USM AF motor system alone. If you are in everyday life often taking a moving object, or a sporting event and need the fastest performance of the system Canon AF lenses, then choose the lens with USM technology in it.