Thanks, flavio. Yeah, that Tamron 90mm is one heck of a glass indeed. When I get the focus right, it produces images so sharp that you can cut your fingers on it!
Unfortunately it doesn't auto-focus on my D40 so it is a kind of hit and miss affair most of the time.
I am a little disappointed that I couldn't get more of the fly in focus even at f/8, but as I mentioned he was hardly there for a second so I didn't have much time to lower the aperture further.