Review on EF 1 4X III Teleconverter Extender by Dave Russell

Crisp, clear optics, minimal XA, acceptable contrast. Build quality was decent but definitely not as solid as a Canon product. Good results on the 7D2 at 400mm f/5.6, autofocus was fast and accurate although the EXIF data was mistransmitted. Poor results at 70-200 f/2.8 IS ii, autofocus didn't work at all, totally useless - manual focus needed. and I think it was also the cause of the strange behavior of the image stabilizer. Eventually, the camera's battery drained at an incredible rate; Even when the camera is off