Damage to Canon EF 50 mm f/1.4 USM

msowsun wrote:

Ray UK wrote:

What happens when the 1.4 is damaged, is as follows:

As the front assembly rotates during focusing it relies on small lugs which run in sloping grooves of plastic tube affixed to the main body. This plastic tube is quite flimsy and any pressure on the front can cause this to be damaged by the lugs.

If the damage is only slight then focusing will still work but the lugs will cause an indentation in the grooves so the focus will tend to stick in this position, this can usually be felt when using manual focus

If the lens has sustained greater damage then the plastic tube will be broken and the front section will not turn at all, so neither AF or MF will work.

Damage caused by pressure on the front of the lens will not affect the lens sharpness unless of course if the lens is unable to focus.

This is the part that is easily damaged by pressure on the front filter threads.

If the lens falls face down and is at the longer part of the focus range the groove can/will be forced open (in the area shown in red). Sloppy focus with lots of backlash is one of the possible outcomes in both manual and auto focus. Unpredictable and difficult to diagnose from a single picture.

I got a used one cheap with this fault and was able to press the "distorsions" back but it took some fancy mechanical measuring equipment to get the ring round and the groove width constant (with a DIY round feeler gauge).