What is USM in camera lens mean ?

If you notice your Canon digital SLR camera lens has the letters USM written on the side, it means the lens has a small motor built into the body. Hence, USM is short for Ultrasonic Motor.

It is important to note that there are two different types of USM lenses. A Ring ultrasonic, is the one you want to purchase. Then there are Micro motor ultrasonic drives that Canon places into their cheaper lenses. Unfortunately, they also letter these cheaper versions with USM as well. While these cheaper versions are quieter, they don't however focus as quickly as a true ring ultrasonic lens. Therefore, you need to check the lens specifications before purchasing to ensure it is a ring ultrasonic lens, and not a cheaper version created for what is rumored to be marketing reasons.

Advantages of using Canons range of ring USM camera lens?

• The main advantage of using a ring USM, is that the motor is built into the lens so that it can auto focus faster than a standard lens.
• Canon's USM / Ultrasonic Motors, are also famous for being quieter than standard motors used in cheaper lenses. This is useful for wildlife photographers, where animals and insects could become spooked from noisy camera parts.

Disadvantages to using a USM camera lens?

• A USM lens will cost you a little extra than one without it.
• USM lenses are generally heavier than standard ones. You might need to take this into account if like me, you tend to carry around 3 at a time.