Canon has long had an ultrasonic motor, or USM autofocus lens focused on a higher speed. Stepping motor, or STM lenses, by contrast, lack speed but make up for it in smoothness.
A History of the Lens Options
If you’re new to photography and just getting started, this brief history will bring you up to speed.
Autofocus lenses in cameras date to 1985, with Canon using a mechanical feature that functioned like a screwdriver, allowing the camera to essentially serve as a motor. A similar structure was used as Canon.
Over time, Nikon, Pentax, and Yashica would incorporate similar systems in their cameras, although Canon would remain the pioneer in the industry.
The autofocus motor being located on the lens became standard over the next 30 years as manufacturers saw the benefits. The Electro-Optical System, or EOS, another Canon creation, arrived on the scene in 1987. This EOS would be a gamechanger for the photography industry.
One of the things about the Electro-Optical System that stood out was its inclusion of two autofocus motors. The standard permanent magnet DC motor connected to the lens, while the second was the novel piezoelectric ring motor, providing torque at low speeds. Elements of this early design might still be seen in contemporary lenses.
What Are the Focusing Motors Used Today?
Canon lenses today use three primary kinds of focusing motor technology. These types include the STM, USM, and DC motors, also known as direct drive. Each of these motor technologies has advantages for different needs.
We’ll take a closer look at these motor types so that you can make an informed decision.
STM or Stepping Motor
STM lenses work well for excellent photos and superior videos. The Stepping Motor, where this technology gets its name, helps the lens focus quietly and smoothly. Because STM lenses are quiet, your video footage will have more natural sounds. Even though lenses are quiet, they are quick enough for most photo needs.
Stepping motors are at their best when used for precise, smooth, incremental movements. Examples include autofocus or AF shooting, particularly during video. When shooting any type of video, smoother movement makes all the difference.
One of the disadvantages of STM lenses is that the focus ring is unattached to any mechanical parts, known as focus-by-wire. In this case, the focus ring’s movement sends a signal to the motors changing the focus position.
Some of the tactile nature found in other focus systems is lost with STM. There are different types of STM motors, and their functions allow them to deal with tactile loss in different ways. The two kinds of STM motors include:
Gear Type STM
Some of the more compact STM lenses include the gear type, driving the focus with helical gears.
Lead Screw Type STM
A larger group of STM lenses use the lead screw type, offering a quieter and even faster experience.
USM or Ultrasonic Motor
When USM technology was introduced during the 1990s, this became the most popular type of AF lens for Canon cameras. All ultrasonic motors convert ultrasonic vibration into the rotational force that powers the lens.
How USM technology works on the basis that vibration frequencies applied to one ring make the other ring rotate. One of the rings attaches to the AF body, while the other connects to the lens body.
There are three USM motor types:
A micro USM motor fits a broad range of lenses without the lens barrel size creating any restrictions. Because micromotors are less expensive to produce, they are ideal for a range of budget lenses. Micro USM motors use gears, working in a traditional manner similar to older AFs. The gears cause less precision and also create more noise.
The Nano USM reached the market in 2016. This Canon technology introduced the best of high-speed AF and quiet, seamless operation.
Many professionals consider this type of motor the best for still photography and videos. The quietness and smoothness are comparable to that of the STM, which appeals to videographers who consider quiet, smooth focus ideal.
The EF-S 18-135mm f/3.5-5.6 IS USM lens was the first to make use of this Canon technology. The use of such lenses helps demonstrate the excellent level of control as the subject moves.
Ring-type USMs power a majority of Canon’s EF lenses. To demonstrate how common this type of USM is in Canon’s line, they are in 42 of the 49 EF lenses available through Canon. There are several features that stand out with this USM type:
- The ability to start and stop faster for a better focus response
- Better holding power so that the lens group stays in place without power
- Gear systems are not necessary for reducing speed because the USMs work sufficiently at lower speeds
Direct Drive or Conventional DC Motors
Camera lens buyers can quickly identify a lens with a direct drive motor by the absence of STM or UTM in the name. Like their counterparts that use STM or USM technology, they also provide autofocus, minus the higher speed, quietness, or smoothness.
Major STM and USM Differences in Summary
Here is a quick comparison to sum up the differences we have highlighted:
STM or Stepped Motor
- Less effort required to focus
- Nearly silent motor
- Well-suited to video shooting
- Works well for beginners
- Much less expensive
UTM or Ultrasonic Motor
- Considerably heavier
- Better overall build quality and weather-proofing
- Focuses much more quickly
- Motor is less quiet
- Well-suited for still shooting
- Professional quality
- Higher cost
Some Final Thoughts
Photographers who need professional-grade lenses for shooting photos will do best with USM lenses. Beginners more focused on shooting videos will benefit more from STM use.
Understanding more about the differences between these lenses will help you choose the best options for your needs.