I use a Sony 70-400 and am very satisfied. Sometimes, the focal length is too little. So I have, after I made some research on the Internet, chose this converter. Focusing is however only manually, and then one should at 1600 ISO and reasonably good light have a very steady hand, or pick up the tripod. Very sharp the images are when doing work with the zoom function of the Sony A55. When taking pictures of animals not always practicing because Viecherchen just lump it in motion. Nevertheless, having bought a good decision this part for my needs (animal and landscape photography).