All Sony E-Mount cameras (apart from the a7S) are fitted with a 2 piece plastic and metal mount, which wears over time, causing “wobble” in lenses. Photodiode has recently released an aftermarket metal mount that can be fitted to Sony cameras. Fstoppers has published comprehensive review and guide to both the replacement of the stock mount with the Fotodiox one and to its subsequent performance. (Image from Fstoppers).