The 'loaner' lens was a dedicated 400mm zeroed at the factory and lacking IS. Further there was no bracket for a tripod mount. Extending it was not an option so I had to up my game and pray a lot that target birds would let me get close for detailed images. Can't say enough good things about trip leaders Wes and Greg when it comes to getting us between the sun and target birds and getting us close enough for detailed images. Thanks again to these guys for going the extra mile (160 miles actually) to make the lens available.