Focusing manually in the AF setting

[ColinC12]

Does manually focusing a lens whilst it is in the Auto Focus setting do any harm? Some lenses specifically allow this but I have never seen anything that definitively states if this practice is harmful to other lenses.

[jdepould]

Depends on the lens. Nikon AF-S lenses and most Canon lenses do it fine.

[inkista]

Originally Posted by jdepould

Depends on the lens. Nikon AF-S lenses and most Canon lenses do it fine.

Dunno about Nikkors, but with Canon lenses, you can damage a lens (by forcing the motor/gears) if it doesn't allow for full-time manual focus. Lenses with ring-type USM allow it. There are a few exceptions (like the EF 50mm f/1.4 USM, which is micromotor, not ring), but if the lens doesn't have USM, you want to remember to flip the switch from AF to MF before manually focusing.

[dakwegmo]

It depends on the lens. Some Nikkors are designed with a manual override in Auto mode. These lenses usually have a switch on the lens labeled M (manual) on one side and M/A (Auto with manual override) on the other. If there's no switch on the lens, you have to set the focus on the camera body, and trying to turn the focus ring could cause damage to the lens. You'll definitely hear/feel grinding gears if you try this.

[mattdm]

Presumably on Nikon or Pentax cameras, where the motor is in the body, you could damage more than just the lens.

Most (but not all) Pentax lenses have a "quick shift" mode, where a clutch automatically disengages when AF is complete, so you can seamlessly switch to autofocus.

[ColinC12]

Thanks for the varied answers so far! To narrow it down I use the following Canon lenses: EF 50mm F1.8, EF 100mm F2.8 USM Macro, EF-S 10-22mm F3.5/4.5 USM, EF-S 55-250mm F4.5/5.6 IS. Is it OK to manually focus these whilst in AF?

[inkista]

Your two USM lenses are both ring-type (10-22 and 100 Macro). The other two lenses (the 50/1.8 and 55-250) are non-USM, and you want to be sure to flip the switch--those are the two you could damage by forcing manual focus.

[ColinC12]

Thanks inkista. There is very little about this in the documents that come with the lens, or anywhere else for that matter, at least where I read!

[jdepould]

Originally Posted by inkista

Dunno about Nikkors, but with Canon lenses, you can damage a lens (by forcing the motor/gears) if it doesn't allow for full-time manual focus. Lenses with ring-type USM allow it. There are a few exceptions (like the EF 50mm f/1.4 USM, which is micromotor, not ring), but if the lens doesn't have USM, you want to remember to flip the switch from AF to MF before manually focusing.

Well there you go.

Really, you should be able to tell by feel pretty easily. On the lenses that allow it, the ring feels the same in M and A. If there's even the slightest resistance, then you probably need to flip the switch.