USM vs STM
I noticed the new autofocus mechanism in Canon's two new lenses, they include a step motor, which is basically a brushless motor for silent lens operation. I wonder if this will completely replace the USM motors in future lens products, or if this is just an addition to USM for certain lenses. I had a look, USM was introduced in the 80s, so this could be a leap ahead in technology.
What do you think?
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