Originally posted by trog100 the lock is purely to stop the lens drooping when being carried or stored and is only capable of being operated when the lens is fully closed...
... we are talking about the tamron 18 x 200 are we not.. ???
Yep, that's the one!
Have to thank John (bfdavis58) for his post. Sounds like it will be correct for another lens, and while it appears he's mistaken about the lock on the Tamron 18-200, his post led to trog's correction, and the net result is that I've finally gotten the answer to my last remaining question about the lens. I did try to some macro shots this afternoon. I tried to use the lock, but I simply could not get it to work at all. Trog's post explains why: it only works when the lens is zoomed all the way down to the shortest length. Just tested it and that's right.
I think the lock is a bit of an odd feature. Maybe it will get "looser" over time, but right now, I can't get the lens to droop when I hold the camera lens down. Nevertheless, I'm happy to know what that button is for.
Will