Lilly W , Sep 20, 2006; 03:46 a.m.
Confusing. Autofocus Lock (AF-L) is a function of the camera, not the lens, unless one of the Focus Lock buttons on the lens is depressed (round, rubber buttons between Focus and Zoom rings on 80-200 AFS; in front of focus ring on 70-200 VR) and, once released, also releases the lock.
<It focuses for the first 10-15 shots and then does not focus anymore.> We'll need a bit more info to sort this one...subject at same distance, which body (bodies), settings, anything else you care to add? Give us your whole scenario re: the situation and what it is you want to do. Hate to answer a question w/ more questions.