My latest project is trying to photograph flying foxes. As they're moving and its dark, I'm pushing my camera's autofocus system to the limit and a lot of the time it just won't lock on (I've only got a window of a few minutes where they're active and my AF still works before getting too dark). I'm finding it a bit of challenge to get a decent shot. But I'm slowly refining my technique, and I'll get there one day. I know the type of composition I want, but I just can't get them to go where I want them! Lens wise, I've settled on the 135mm. Its the only fast telephoto that I've got. Being sharp wide open makes it a natural choice. It's an awesome lens.