When we choose a lens for photography or a film, a few first things that we repair were a focus or blur of the image.
Since 1987, when Canon became the first company to integrate an objective lens engine, several engines have been introduced. These motors are designed to obtain and enhance the focus of fast-moving objects for greater precision, smoothness, and silence.
There are currently three main types of engine technology that are used with Canon lenses. These include STM, USM, and a more conventional DC motor. We look at the differences between these engines so that you can understand and select the objective according to your needs.
What is Canon STM Lens
STM is the name for an autofocus motor from Canon. All STM lenses are equipped with this special motor.
STM stands for "Stepper Motor" and this allows the lens to focus evenly and quietly. In a stepper motor, the rotor is turned by a controlled, step-by-step rotating electromagnetic field. The even and quiet focus makes the lenses excellent photo lenses but is even better suited for video recording.
The low-noise focus means that the surrounding noise is not superimposed and the sound of the video is not impaired. It is surprising that, despite this extremely quiet autofocus, the lenses are still able to be fast enough for almost all photo situations.
Canon uses two different drive alternatives for the stepper motor. For the smaller and more compact STM lenses, a gear drive is used, which is driven by a helical gear. Canon handles this a little differently for the more expensive and larger lenses. A screw spindle drive was developed for this. Compared to the gear drive, this is even faster and quieter and therefore a real quality feature for a lens.
The Canon STM system is excellent and will convince anyone who values good autofocus. In addition to the autofocus, STM lenses are also excellently processed, making them a good option for every photographer. Canon's STM technology provides a range of lenses that are extremely quiet and also fast enough to capture photos in most areas.
A more compact and smaller range of STM lenses, including the EF 50mm f / 1.8 STM, included a very compact STM motor that uses a helicoidal engine for targeting.
What is Canon USM motor?
USM (Ultrasonic Motor) or type of automatic focusing motor (AF) is most used in the range of EF lenses from Canon. Common to all USM motors is the fact of converting ultrasonic vibrating energy into rotational force to move the lens. This is currently the fastest motor of the Canon range, which allows even manual adjustment of the focus without having to fully disengage automatic focusing.
USM is found in most of the professional Canon objectives. It allows greater control and provides great speed and precision. The USM motor is powerful enough to transform groups of heavy lenses into large telephoto lenses quickly and easily if you need to go through a gear system to reduce speed.
USM engines also have high retention power so that whenever the engine is disconnected, or the target group of focus remains fixed as long as any other action is required. USM motor is not as silent as many STM motors, but it is still extremely silent having in contact or its performance.
USM mechanism is composed of a rotor and a stator (an elastic body with a fixed piezoelectric ceramic tensioning element). When applying an AC current with a resonant frequency at about 30,000 Hz to the stator, vibrations are created that cause continuous rotation of the rotor. The value of 30,000 Hz is not found to be an ultrasonic interval, this being the main factor for the second.
Nano USM is the most recent innovation of Canon in the powered focus technology. Announced at the beginning of 2016, it combines the speed of USM with silence and smoothness of STM. The characteristics of this type of turning motor or motor ideal for capturing fast-moving films with a quiet and smooth focus are the ideal characteristics.
Inside the Nano USM unit, there is an elastic metal body, a ceramic tensioning element, and a motor. The application and adjustment of the tension for the ceramic element control the direction and speed of the motor. The result is a targeting system that offers smooth targeting with great speed control.
Understanding the difference between STM and USM
According to the photography experts, STM motors are better suited for video because they focus more smoothly. USM is faster than STM, but the focus is too jerky for videos.
USM (ultrasonic) motors are like magnetic levitation trains, also technically similar in that they work without contact: Incredibly fast once they are on the move, but they take a long time (relative to STM) to come up to speed and to brake. And they are not so good at "maneuvering".
STM motors (stepper motors) are more like Formula 1 cars: fast, but not as fast as a magnetic levitation train at top speed. Quickly up to speed, incredibly precise steering, and brake quickly. This is why STM motors are better suited for video because the smallest back and forth movements have to be responded to quickly and gently at the same time. STM can do that better than USM.
However, a distinction must be made here between ring USM and micro USM. Ring-USM is very precise and also very fast, often faster than STM. In addition, the noise level for humans is equal to 0 and they can also be accommodated in a very space-saving manner.
Another big advantage: You can intervene in the focus at any time, even when the lens is on AF. Disadvantage: There are definitely noises in the higher frequency range - whoever photographs animals must know that.
Overall, STM has advantages that make it ideal for DPAF and video. The Nano-AF is probably a bit better. But everything is actually equally good for photos and videos, so it all comes down to your personal preference.