It's a bit more complex: currently Canon uses already 2 versions of STM AF drives: gear type for most compact build and lead screw type for better stills performance.
http://www.usa.canon.com/cusa/consumer/standard_display/Lens_Advantage_Perf#usm
There will be no EF-M lenses with USM drive. Thanks to Canon sucking up to the video minority. One of so many video-induced compromises forced upon photographers. But i can happily live with STM AF - even the cheapo gear-drive STM version in 2 of my pancake lenses (EF 40/2.8 and EF-M 22/2). I do prefer Ring-USM in DSLR/phase-AF lenses. But on "live view only" mirrorless cams with contrast AF detection or hybrid on-sensor phase detect + contrast AF, STM is a reasonable - maybe even superior at the moment or until next gen USM drives are launched. Fine with me, no real issues in daily practice.
http://www.usa.canon.com/cusa/consumer/standard_display/Lens_Advantage_Perf#usm
There will be no EF-M lenses with USM drive. Thanks to Canon sucking up to the video minority. One of so many video-induced compromises forced upon photographers. But i can happily live with STM AF - even the cheapo gear-drive STM version in 2 of my pancake lenses (EF 40/2.8 and EF-M 22/2). I do prefer Ring-USM in DSLR/phase-AF lenses. But on "live view only" mirrorless cams with contrast AF detection or hybrid on-sensor phase detect + contrast AF, STM is a reasonable - maybe even superior at the moment or until next gen USM drives are launched. Fine with me, no real issues in daily practice.
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