Why do high-end Canon lenses use USM instead of STM?
Asked 1/7/2015
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Canon offers lenses with both USM and STM focusing motors. STM is known for quiet, smooth autofocus that works well for video, while USM is often described as faster for still photography. Why do many higher-end Canon lenses, especially L-series lenses, still use USM rather than STM?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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Like many things when it comes to designing hardware for photography, there are always tradeoffs to be considered and made.
STM lenses sacrifice a little speed in order to be quieter and smoother (no jerky starts and stops). This is important when using Autofocus while recording video.
Lenses with USM focus designs are built for speed first and quiet operation second. Since they are optimized for still images, the jerky starts and stops that help them get there faster are of no consequence.
More advanced videographers tend to use manual focus, often with external focusing rigs that attach to the lens and allow much finer manual focusing control, and also enjoy the benefits of the superior optics in many "L" series lenses. That is, if they are not using the even more expensive Cinematic grade lenses that in addition to superior optical image quality include such features as parfocal zooming and corrections to eliminate focus breathing (but no AF).
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
11y ago
0
Generated from our catalog & community — verify before relying on it.
Because they’re optimized for different priorities. STM is designed for smooth, quiet focus transitions, which is especially useful for video where abrupt focus changes can look and sound distracting. USM is designed primarily for speed, which matters more for still photography, especially action, sports, and wildlife where fast autofocus tracking is critical.
High-end and L-series lenses are often aimed at photographers who prioritize fast AF performance for stills, so USM remains the better fit. The “jerkier” start-stop behavior that can be a drawback in video usually doesn’t matter for still images.
For advanced video work, many shooters also prefer manual focus or dedicated cinema-oriented gear, so the smooth autofocus advantage of STM is less important in that segment. In short: STM is favored for quiet, smooth video AF; USM is favored for faster still-photo AF.
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