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new EF-M 32mm f/1.4 coming! Price???

Started Aug 28, 2018 | Discussions thread
nnowak Veteran Member • Posts: 9,073
USM vs STM vs Nano USM
5

There seems to be a lot of confusion in this thread about the different focus motor varieties.

USM - This is a ring type motor roughly 5mm in cross section and with a diameter almost as big as the lens using it.  Think of it as an electronic hand that spins the mechanical focus ring.  One rotation of this motor = one rotation of the focus ring.

STM - This is a very small can motor to one side of the optical path.  Instead of a shaft like a typical motor these are designed with a hollow, threaded core.  When the motor spins, it drives a treaded screw in and out.  The threaded screw is directly connected to the focus group.  This motor needs to rotate numerous times to cover the entire focus throw.

Nano USM -  Electrically, they are a USM moter, but instead of a ring, the motor is a flat line.  Like STM, the motor is directly connected to the focus group.  These are also called "linear" motors and they are often used in mirrorless lenses from other manufacturers and are often used in multiples.

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