I've had my gear for about 4 weeks now and as I become more familiar with it, and a little more practised in the using it, I think I've found a problem with the above-mentioned lens on my D90.
I first noticed a problem with AF a few days ago, and today my colleague - a D40 & D90 owner - confirmed and characterised the problem further. Furthermore, he says his 18-200 VR (I) doesn't (mis)behave like this!
To re-create the problem, we zoom out to 200mm and focus on an object 20-30m away. Then we turn the manual focus ring so that it is (maximally) out of focus, and then half-press the shutter button to engage AF. Trouble is, it generally won't re-focus at all, and simply beeps as if it is in-focus. If you press the shutter button again a couple of more times, it will eventually "get the hint" and manage to focus correctly.
The camera is to set P mode, AF-Auto and we've tried both single-point and area focus. The lighting is a bright sunny day, and the frame has plenty of contrast.
We tried to repeat indoors (obviously at closer distances) but could not reproduce the problem nearly as readily; only managed to when all the contrast was towards the left of frame rather than in the middle. I also tried again at home tonight, but couldn't reproduce the problem.
My question is this - is this "expected" behaviour? Should I expect the autofocus to simply "give up" at times when it is horribly out of focus? My instinct tells me there is something wrong here...
I should also add that initially I was having problems focusing on a very high contrast sign some 50m away. If the focus just happened to be close, but not perfect, then the AF wouldn't engage at all. But re-framing on something about half the distance, focusing, then re-framing on the sign would bring it into perfect focus.
I've given the store a heads-up but they say they have to send it away for testing to their technicians, which I'm loathe to do because (a) I won't be on hand to explain the issue and (b) I bought the camera for an OS trip in 4 weeks. Also, it's a gray import which means I don't have an Australian Nikon warranty...