Geoff, thanks for the tip...
luckily I normally carry loads of books to school, which weigh more than double my camera kit!
Another tip, sometimes attaching and detaching the Lens Hood will not work unless you twist by holding the textured bit of the hood, near to the bayonet fitting.
another tip is to double check the tripod mount when you put it onto a tripod, as a loose mount can put strain on the lens, which is partly made of plastic
one question... what exposure settings do you try to use when shooting through glass??
Will