I used this with my Minolta 50mm and 100-400mm which effectively gave me 100mm and 200-800mm respectively while keeping auto focus functionality. Works on Sony LA-EA4 adapter too if you use A-Mount lenses on your Sony mirrorless camera. In other words, this teleconverter carries out the focus drive (assuming you are using a screw drive body, or an adapter like LA-EA4) and communicates other information thanks to the electronic contacts (i.e. it is NOT one of those manual, dummy teleconverters). The only down side is it will double your aperture i.e. f/1.7 (lens) -> f/3.5 (with teleconverter) which is by design. I believe MC4 in the model name refers to 4 elements, unlike the MC7 (with 7 elements). Therefore it is priced accordingly.