In sony a6400 tested with yongnuo 50mm f1.8, Tamron 17-50 f2.8, and Tamron 70-200 f2.8. With the yongnuo, it does not recognize the aperture and permanently shows f/4 no matter what you do. Also, at some point, when you open the aperture from the camera, it makes a "bang" sound and fully opens the aperture, resulting in an overexposed image. Additionally, the autofocus does not always work, and even when it does, it never manages to "lock" onto the subject and stay focused. It constantly hunts for focus. With the Tamron lenses, it correctly displays the f-stop, going from 2.8 to 2, and indeed makes the lenses faster. However, the autofocus still has the same issues, whether in phase detection or contrast detection mode. I have tested it with all available firmware updates, and none of the problems were resolved. I discourage anyone considering purchasing it. It is the most wasted 150 euros I have ever spent in my life. Stay away.