A walk round the lake was the ideal opportunity to try my new lens - an Olympus OM Zuiko 200mm f/4. Looks pretty good for a first try although the manual focus takes a bit of keeping up with. I'm out of practice.
I've gone for this lens as I'm fed up with the poor quality of the 70-300mm zoom and it's affordable..
Next to search for is a Nikon 300mm f/4.5 which seems to be better regarded than the Olympus OM version.