I recently upgraded my long lens (300mm), buying a newer model with faster autofocus. One of the issues using long telephoto lens is your technique and focus. I had to work through some of this with my old lens and the new one is finicky so far. I made the mistake of not calibrating the lens thoroughly before heading out. Of course Murphy's Law comes into play as I some really good opportunities to get pictures of some birds including this eagle and more harriers. This eagle shot came out pretty well, but many of the others didn't come out well as I would have expected. Need to spend more time working out the kinks and re-calibrating the new lens with my camera. Let the fun continue.