Oh by the way, I saw helicopter G-CGDW fly overhead twice, incase that's of any interest to you helicopter guys. I presume it's a Robinson or something.
Thanks for the comments, the lens was the Canon 70-300mm IS USM. Very happy with the lens, it seems to be perfect for aviation spotting at Belfast. I ordered a Kenko 1.5x convertor yesterday just to try it out for fun. It will reduce the light into the camera meaning almost certainly autofocus will stop functioning however I will see how it goes. It should work ok with manual focus but obviously for aviation spotting, automatic is best.