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What's the reason that many of the newer mirrorless lenses are switching to stepper motors verses the ultrasonic and similar motors of the past?  Does it allow them to eliminate position sensing elements?  (cost)?


Brian

Much better and smoother focus performance for video where all AF is done on sensor, even on a DSLR (using the live view capability).  It is much quieter than USM motors so there is no risk of focus motor pickup on videos.   Also, better performance on mirrorless cameras on still shots due to the AF being done on sensor rather than off sensor as it is done in a DSLR.  It allows much better contrast detect while maintaining phase detect capability.  Most mirrorless systems these days use phase detect first and fine tune with contrast detect which gives you more accurate AF without the need to AF fine tune your lenses.  USM motors perform relatively poor on mirrorless cameras in comparison.

Thanks E.J.

Brian