Why are USM lenses more expensive?
“USM” signifies the lens has an UltraSonic Motor for autofocus. That means AF is faster and quieter then the less expensive lens, which uses a conventional motor. … The more expensive lens is 0.5 stops faster at 17mm (f/2.8 vs f/3.5) and a full 2 stops faster at 55mm (f/2.8 vs. f/5.6). Thereof, What is […]
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