What do the letters USM vs STM on Canon Lenses mean ↑
When you are looking for Lens Canon you may see the Suffix USM vs STM.
- USM stand for Ultra Sonic Motor.
- STM stand for Stepping Motor.
Both USM vs STM mention about the focus technology was used in Canon lens.
USM variety exists in two flavors, the Ring USM, and the Micro-USM, but the STM variety also comes in different applications.
Ring USM ↑
Ring USM was the firts UltraSonic Motor technology introduced for AF lenses in the 90s by Canon. It’s based on the fact that if certain vibration frequencies applied to one of the two or more loosely coupled rings, causes the other to rotate.
One Ring is secured on the lens body, the other on the AF group and drives it directly.
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.
Micro USM ↑
The Micro USM used a similar sonic vibration motor, but instead of directly coupling with the AF group, a series of gears was used resulting to a more traditional AF drive approach. The motor itself was silent, but similarly with regular DC motor solutions, it is the gears that created most of the noise to begin with, and added some slack in the precision.
The motor and the gear:
When you see a Canon lens with STM in the name, it means that it features Canon’s Stepper Motor technology. Canon introduced this motor design to be a quieter and smoother focus system that allows for near silent focus during video recording.
The downside to the technology is that the lenses are focus-by-wire, which means the focus ring isn’t attached to a mechanical mechanism at all. Instead, the movement of the focus ring merely sends a signal to the motors electronically to change the focus position. The means you do lose a lot of the tactile nature of regular focus systems.
Without any gear involvement, this assembly can allow for very precise movement, and the stepping motor itself is meant to be rotated with extreme precision based on the pulse modulation, in a way that allows the camera to know where exactly the AF group is, instead of just waiting for the approximation from the AF sensor. Once AF lock is initially confirmed on a moving subject, and if the movement of the subject is within the AF sensors tracking capabilities, the STM motor can smoothly focus track it without back and forths, in a way that in theory the USM motor – ring or micro – cannot.
USM vs STM Which is better ↑
STM (Stepping Motor) is built for a smooth auto-focus. USM (Ultrasonic Motor) is used for achieving speed for moving subjects. On the other hand, USM is onto the pricier side and also is quieter when compared to the STM.
Point to be made is: If you are into wildlife, moving subject photography, then it is preferable to go for the USM lenses. While STM help you in shooting still subjects perfectly!