Explaining the Different Types of Lens Autofocus Motor | Fstoppers

This motor is known as the most basic and economical autofocus motor. It consists of a small electrical motor that moves the lens elements to achieve focus. Micro motors are very compact and lightweight, which is suitable for constructing smaller lenses. It also usually focuses slower and noisier compared to the other autofocus motor types compared to more advanced motor types. As this motor is economical and cost-efficient, it is commonly found in cheaper and entry level lenses.

Example of lenses that use micro autofocus motors: Two Phase Stepper Motor

Explaining the Different Types of Lens Autofocus Motor | Fstoppers

Canon EF-S18-55mm f/3.5-5.6

This motor is an improvement over the micro motors. They provide a more pleasant, faster and quieter autofocus experience. DC motor works by using the direct current power source to drive the lens elements for focusing. While the DC motors may be considered an upgrade over the basic micro motors in terms of focusing speed, they are still relatively affordable and may not provide the most precise autofocus. Hence, they are usually found in mid-range lenses.

Example of lenses that use DC autofocus motors:

This is the motor that is commonly used among the higher-end lenses, as the cost is higher compared to micro and DC motors, especially those produced by Canon. This USM autofocus motor is known for their fast, accurate, and nearly silent autofocus operation, making it desirable for sports, wildlife, and fast action photography. This technology uses ultrasonic vibrations to drive the focusing elements. There are two main types of USM motors, the Ring type USM and Micro USM. Ring type USM motors are larger and faster, which makes it suitable for larger telephoto lenses, while Micro USM motors are smaller and lighter, making it suitable for compact lenses.

Example of lenses that use ultrasonic autofocus motors:

Silent Wave Motor is basically Nikon’s equivalent of Canon’s Ultrasonic Motor. It also offers fast, silent, smooth, and precise autofocus experience, which is well suited for various photography genres, including wildlife and portraiture. The SWM motor uses electromagnetic waves to drive the focusing elements. Like the USM, SWM is also available in two types of motors, the AF-S (Single Motor) and AF-P (Pulse Motor). Each comes with its own characteristics that can be optimized for specific lenses and purposes.

Example of lenses that use silent wave autofocus motors:

Nikon AF-S NIKKOR 24-70mm f/2.8E ED VR

Nikon AF-S NIKKOR 70-200mm f/2.8G ED VR II

Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED

Linear motors are commonly used in lenses made for mirrorless cameras. This autofocus motor provides quick and quiet autofocus performance which is suitable for video recording. The linear motor works by using electromagnetic fields to move the focusing elements along a straight path, as stated in the name. It has the capability to offer high-speed focusing and precise control, which contributes to improved tracking and subject detection used in continuous autofocus modes.

Example of lenses that use linear autofocus motors:

Fujinon XF 23mm f/1.4 II

Stepping motors are also frequently found in mirrorless lenses, particularly those designed for video shooting and smooth focus transitions. STM technology offers silent, precise, gradual adjustments of focus and minimal abrupt changes during autofocus. As a result, it is often slower than other motor types in certain scenarios. STM motors are suitable to be used for video recording with continuous autofocus. 

Example of lenses that use stepping autofocus motors:

When selecting the right lens, photographers should take into consideration the level of autofocus performance that is needed. From there, they will be able to select a lens with a specific autofocus drive. These factors include autofocus speed, accuracy, noise level, compatibility, and reliability. 

Having learned about the different types of autofocus motors, we know that some lenses are made and designed for newer mirrorless technology. So, for photographers who wish to migrate into mirrorless systems and future-proofing their equipment, they may want to consider lenses that are made with modern autofocusing motors.

Different autofocus motors will provide photographers with different user experiences. Some lenses provide a pleasant user experience by providing a fast, silent, accurate, and precise autofocus, while some are just the total opposite. These experiences should be considered before purchasing a lens to ensure that the purchase is suitable for photographer’s usage.

The type of autofocus motor can impact the price of the lens. Advanced autofocus motors such as Ultrasonic Motor and Linear Motor that cost more are often found in higher-end lenses and may come with a higher price tag. This is where the photographer’s budget comes into play in determining the right lens to get while weighing the autofocus performance and their photography requirement.

Different types of lenses are designed for different types of purposes. Genres such as portraits, landscapes, sports, macro, or general-purpose photography will have a different level of hardware requirement. Therefore, before purchasing the lens, the photographer should consider the specific requirements of your photography style and choose a lens that matches your needs. For example, fast-moving subjects may require a lens with a faster and more responsive autofocus system and vice versa.

In conclusion, selecting the appropriate autofocus drive for a lens requires careful consideration of various factors. While the advantages and disadvantages of different autofocus motor types provide a helpful starting point, it's important to recognize that performance can vary within each category due to lens design, firmware optimization, and other variables. The guidance provided in this article serves as a valuable resource for photographers, offering considerations such as budget, intended usage, system compatibility, and the desired balance between speed, noise, and reliability. By taking into account these factors and conducting thorough research, photographers can make well-informed decisions when purchasing lenses that align with their specific needs and preferences.

Yang Zhen Siang is a commercial photographer specialising in architecture, food and product photography. He help businesses to present themselves through the art of photography, crafting visually appealing and outstanding images that sells.

Very interesting article! Well done and thank you very much.

Thank you for taking the time to read Vag Liu

Thank you for explaining things to me that I didn't already know. I like to learn new things about camera gear!

Thanks for taking the time to read Tom, will share more in the future

Do motors differ in how they hold a long duration fixed focus, such as during astrophotography?

For example, I know stepper motors naturally hold their position forever when no power is applied, i.e. they require power in order to step. But I assume a linear motor, a.k.a. voice coil motor, requires constant power to the voice coil to maintain a constant focus position, unless the lens has some kind of brake. And if it doesn't have a brake, would there be constant micro movements that affect focus as it's internal feedback attempts to maintain position? If some motors require power to maintain focus position, wouldn't that affect battery life?

That is an excellent question, and I am looking forward to the answer that explains this aspect of each of the motor types. It is frustrating beyond belief to have focus change a wee bit when I have done nothing to change it, yet this seems to happen with all of my lenses.

A good motor should hold precise focus no matter what - even if someone shakes the camera around and does jumping jacks with it held overhead, it should not change focus AT ALL unless focus is intentionally changed. What motors do this with absoluteness, and which ones let the focus slip when the camera is jostled around? And to which extent does each type of motor allow this to happen?

the zoom ring does also shift a little when dealing with weights from the lens group itself. My solution whenever I am shooting stationery subject with zoom lens is to tape the zoom ring and focus ring itself. However this does not apply to those lenses with electronic focusing or electronic zoom.

Hey Eric, this is a good question and it did not cross my mind at first as I was not troubled by it most of the time unless dealing with lenses that has large and heavy lens groups.

I have done some google search and came across this article that has a much detailed explanation on lens motors. Under the ring type usm they did explain about the motor designed to have a high levels of holding power to hold the focusing lens group in place when there is no power directed to the motors.

Do check out this article. and hope its helpful for you. I am surprised this topic is not covered by much people.

Hello Zhen, I have a question, I use Hasselblad optics on a digital camera, obviously these lenses only work in manual mode, I must remove all automation from the camera for it to work properly, Thank you from Puebla, Mexico.A hug.

Explaining the Different Types of Lens Autofocus Motor | Fstoppers

Small Dc Motor Hi Victor, thanks for taking your time to read and comment. Do allow me to reply in English as I am not fluent in your language. I do not have much experience with Hasselblad glasses. But I assume they would work digitally with Hasselblad bodies. In other cases of adapting into other cameras manually I do not think they are going to work as they have leaf shutter in the lens itself. You might need to find an adapter with electronic controls. Older Hasselblad lenses with no electronics might work with just manual adapter. Hope I did answer your question.