I was using my 20-35mm f2.8 AFD Nikkor the other day. When I switched the lens back to manual focus (using the button on the lens), the focussing ring refused to engage with the focus gear. The focus ring just kept turning and turning. Normally, a quick twist either way of the ring engages the focus mechanism. Eventually. it worked, but now I'm in the position of not wanting to use it on AF again, just in case the same happens again. Anyone had a similar problem? Regards, Blights.