Yes, the FE 50mm f/1.8 is compatible with the Sony a5100, but with restrictions: -SteadyShot mode is not supported. -When the camera enters standby during video mode and during video recording, the lens switches to manual focus. If you update the camera's system software to version 3.10 or higher, autofocus will be activated. -AF-A cannot be selected in focus mode. Phase-detection AF with focal plane not supported. If you update the camera system software to version 3.10 or higher, you will be able to use AF-A mode and focal plane phase detection autofocus.