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The lens manuals for my lenses without "full-time manual focusing" warn not to use the focusing ring when it's in Auto-Focus mode. I assume that even applies when the camera is off, but am I being too paranoid? A common use case is to compress the lens to its smallest size when packing it away. How bad is this really?

(Edit) My camera is a Canon T1i, so no in-body focusing motor. A friend has the XTi, also without an in-body motor. I've seen people be pretty casual about "shortening" their lenses in order to fit back into their camera bags. I've also seen people pick up telescoping lenses by the exposed (extruded?) portion of the lens instead of the normal zoom/focus part of the body. At what point are we risking harm to the lenses?

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Not having full time manual focusing still means you have both Auto and Manual modes, if I am correct. With lenses that have a manual mode I have not faced any problem at all- I do this regularly. After turning off the camera, I switch to manual, twist it to shortest length and switch back to Auto to keep it in place.

  • Rajib, I used to the same too, but found myself sometimes skipping the focus-switch step, and so I've wondered if that's a problem. You don't really say that there's a problem, you just say you're following best practices. :-) – Michael H. Jul 21 '12 at 18:36
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Some lenses are driven by a motor in the camera (usually higher-end or older ones) - in "compressing" the lens you will be driving the motor in the camera. - in Nikons this is a little slotted pin in the mounting ring - this is not on the lower-end cameras.

Switching to manual focus retracts the drive pin back into the cmaera body, allowing the focus ring to control the focus alone.

This applies with the camera on AND off.

In theory if you drive it too fast (with the AF motor engaged) you could cause damage to gears either in the lens or in the camera.

Simples :-)

  • Hi there! Thanks. Simple, but I don't believe it applies to my case, since my Canon doesn't have in-body motor. I'll add that to the question. – Michael H. Aug 2 '12 at 15:40
  • Also note that moving the motor induces a current that goes back into the electronics, but i'd say the device is engineered to withstand that. – Barry Staes Jan 20 '15 at 9:06

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