Hi Michael,
I've never used my camera/stabilised lens on a tripod (I bought the lens specifically to avoid using tripods!
) but there seems to be a lot of conflicting information out there about IS (or OS for me, it's a Sigma lens) and tripod use.
The instructions with my lens - and much online commentary - say "switch it off if you're using a tripod", and this seems to apply (in the eyes of many people) to Canon and Nikon stabilised lenses too.
Then occasionally I read something to the exact opposite efect, posted by someone like yourself who clearly combines approaches successfully..!
Kim,
when all's said and done that's a sharp blue tit, so it can obviously be done hand-held, and hiking the aperture up to f8 will certainly have helped with the overall sharpness.
As an aside, I did notice that the heron's feet and the mud and water that its plodging through looked nice and sharp sharp, so I'm wondering if you auto focussed on the wrong part of the scene instead of the eye, as Michael recommends...