That's why many people (me included) use back-button AF, where a shutter half-press activates metering only, and you press teh AF-ON button to AF.I've seen that option. Was looking for the opposite, something to stop the AF while in AI servo mode to change the framing without losing focus. I did find that...
I guess that if you use back-button AF instead, you can just stop it servo-focussing by releasing the button? Personally I've not tried it yet, but I did find that back button a bit fiddly to find (for AF stop) for something as important as focussing.
And you're correct, it might have been the 85L. But it was either that or the 135L, it was an 'odd number'. But it was an f/2 prime for sure. The person who had it didn't know much about it either (she had just got her new body for a week and borrowed the lens from a friend or something).
Thanks for yet another explanation.
I use the AF-ON button to stop my AF, which it sounds like you've tried? I'm used to the shutter button metering and auto focusing, so whenever I want to manual focus, or lock focus for a series of pictures, I hold the AF-ON (made to be AF-OFF with a custom function) until I want to use auto focus again. I will switch the lens to manual focus if I want to keep it locked for more than a few pictures.