Lens in question, Canon 50mm F1.4 microUSM.

The lens belongs to a friend of mine. He told me that it was being tried out by a friend of his and he observed this person turn the focus ring (in MF) beyond the calibration markings, and he continued to turn it until the slight resistance registered with him. Perhaps 60deg too far, but without using force. The friend was expecting the ring to reach a stop position and only gradually reacted to the slight change in feel in the focus ring as it was turned beyond the calibration markings.

My friend now thinks the lens is front focusing. He ran the lens through tests after he bought it about 6mo ago. Now, after he became suspicious that the over-turning of the focus ring had damaged the focusing performance of the lens, he has repeated those tests.

I told him I would seek some advice here about whether it is likely that over-turning the focus ring would damage the lens.

It's a bit shocking if damage can be caused in this way. There is no warning about this in the documentation with the lens, and the overturning was basically accidental and not abusive.

Any reactions gratefully received.

Thanks.

Neil

Over-turning the focus ring will not cause a lens to start front-focusing. The 50/1.4 is a bit kludgy in the focus design, with a 'clutch' to allow FTM focus. But even if somebody were to break this mechanism through abuse, it would not cause the autofocus to consistently front- or back-focus if it wasn't doing it before.

moondigger, much appreciate your reply. Thanks.

Neil