STM vs USM: Canon’s Lens Tech Explained

In this article, we’ll compare Canon’s STM vs USM lenses and learn which is best to snap on your camera for your next video project.

While the focus (pun intended) of amateur filmmaking has pulled towards mirrorless cameras in recent years, it was the age of the DSLR that truly reshaped Canon’s approach to camera glass.

Before Canon made it possible to capture cinematic video with DSLR cameras like the Canon 5D Mark III, camera lenses prioritized a speedy autofocus above all else. It makes sense. What Canon shooters wanted most out of their AF systems was fast, reliable focus. If the German bobsled team is hurtling down the track at 90 mph, photographers can’t rely on frantically tapping their iPad screens to dial in on those super sleek helmets.

The latest in bobsled helmet fashion.

Motorized focus changes the game

Enter the USM (or ultrasonic motor). First introduced in the 90’s, USM lenses continue to be the fastest Canon glass in the Olympic park. Fast and abrupt, USM lenses aren’t afraid to make a little noise. 

But when more and more hobbyists started buying DSLRs for their video productions, Canon saw an opportunity to retool the autofocus system and introduce the STM (or stepping motor) that emphasized smoother focus pulling and quieter motor noise. 

Today, STM lenses offer beginner videographers an alternative to heavier and more expensive USM glass built more specifically for their needs.

USM design & function

While the 90’s may feel like ancient history, Canon’s USM technology still seems like science fiction. As the name suggests, USM motors convert ultrasonic vibrations into the force required to rotate the focusing elements of the lens. How these motors actually harness this ultrasonic vibrational energy is a story for another science lesson, one which I am glad I’m not required to explain.

What I can explain is that there are three types of USM motors:

• the micro USM
• the ring-type USM
• the nano USM

For our purposes we’ll be talking mostly about the ring-type USM, as it is the motor used in the vast majority of Canon’s lineup (at last count used in 42 of 49 Canon USM lenses).

Micro USMs

The micro USM is the motor typically used in your everyday kit lens. You can think about the micro USM as the tiny little cheapskate of the family. Cheaper to produce because they fit in a wide range of lenses regardless of barrel size, they are also loud little buggers. While you might expect an ultrasonic system (which is literally any sound that is too high to hear by humans) to be completely silent, the micro USM is actually quite noisy. 

If you have a kit lens on hand, pop it on your camera, switch it to autofocus and hear the mechanically whirring as it hunts for the focusing subject. While the micro USM itself is silent, the coupling with cheaper-to-produce gears make the grinding sound that reminds me of a remote-controlled car. 

Micro ultrasonic motors

Ring-type USMs

Ring-type USMs, on the other hand, work using ultrasonic energy to rotate rings uniquely designed to each lens. Like I said, don’t ask me to explain how that works, because I’m pretty sure it takes a physicist. But the main takeaways are as follows:

• Though ring-type USMs produce enough power to avoid using a gear system, which as we’ve discovered can be quite noisy, the moving glass elements still generate a bit of noise which is especially audible through your camera’s internal microphone (example below). 
• Ring-type USMs are powerful enough to hold the focusing lens in place when the motor is switched off allowing the shooter to switch seamlessly between auto and manual focus.
• Ring-type motors start and stop quickly, ensuring fast response times. This is ideal for photography, but results in an abrupt rack focus for video.

Ring-type USM

Nano USMs

The nano USM is the newest and sleekest of the three. Released in 2016, the nano USM is able to operate just as quickly as the ring-type while also achieving smooth and silent operation. You can think about the nano USM as the sibling who Canon spoiled because they were the youngest child. Combining speed, silence, and smooth moves pretty much leaves the USM vs STM competition in the dust, but because the motor is still so new and limited to a small selection of lenses, the battle rages on. Come future technology, bring us sweet decision-less peace.

Nano Ultrasonic motor

STM design & function

If you rely on your camera’s internal microphone, lens noise can ruin a great shot. Fortunately, Canon brought us the STM.

STMs come in two varieties:

• the gear-type STM
• the lead screw-type STM

As you can imagine, anything with gears to grind is going to be noisy. But the lead screw types are where STMs shine.

The motors achieve their lower noise levels by running (or stepping) back and forth along lead-screws within the barrel of the lens. While not as quick as ring-type USMs, these motors move along the screw more gracefully, and quieter too.

Lead screw-type STM

On the other hand, while ring-type USM lenses don’t make any noise during manual focus, STM motors maintain a consistent level of noise when turning the focus ring in both auto and manual modes (though it’s not very much).

STM motors are typically found in lenses specifically marketed to amateur video shooters. The technology is cheaper to produce than USMs. Therefore, STM lenses tend to be more affordable. That said, even though they are meant for video purposes, they are still relatively fast to autofocus and can definitely still be used to capture terrific pictures.

Here’s a great example of the differences in focus pulling and noise of STM vs USM lenses:

STM vs USM Lenses: Pros & Cons

STM vs USM lenses: Wrap-up

In summary, STM lenses are ideal for beginner video shooters on account of quiet motor noise and smooth autofocus pulls. STM lenses also tend to be more affordable, which is great if you’re just getting started.

But if I said it once, I’ll say it again, you shouldn’t rely on your camera’s internal microphone for very long. When you can afford an external mic and audio recorder, cheap as they may be, your production quality will take a huge leap forward while also shrinking the issue of motor noise. 

When your audio improves and you start earning more from your productions, a USM lens might start to look like the better option. Though the rack focus is slightly more jarring, the advanced optics and speedier motor can be a big deal for video shooters (such as vloggers) who rely heavily on autofocus functionality. If you have the budget to spend more on Canon’s L series (all of which use USM motors), the picture is markedly improved and the lens quality is about as good as it gets.