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I have a EF-S 18-55mm 1:3.5-5.6 III, and want to know what is the worst-case scenario if you move the focus ring in AF mode?

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You could damage the motor

The manual focus ring is a miserly 3mm wide, and rotates less than 60 degrees clockwise from infinity to 0.25m. It also rotates on autofocusing, so care must be taken not to grip it during use, to avoid damaging the motor.

If the focus ring turns during autofocus, assume that it is directly attached separate from the motor.

A lens built to be cheap can't be presumed to have a robust and reusable torque clutch; at best something is designed to slip before anything breaks, but it's just plastic on plastic and actually using it will loosten it up. So it's like a car bumper if it exists at all: use it and expend it.

  • SO if i broke it i wont be able to autofocus ,but i can still focus prefectly in MF? – Stanley Sep 27 '15 at 7:48
  • If you break the motor or drive train, hes. If you wear out the slipping part that protects the motor, then vice versa and the manual ring will be loose. So either could break, or both. – JDługosz Sep 27 '15 at 21:00

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