Sony have released a firmware update for the 18-105mm lens that is available as a package with the FS5. The update addresses some of the focus tracking issues that some lenses appear to have. To update the lens firmware you need to go to the support page of Sony consumer: http://www.sony.co.uk/support/en/product/SELP18105G
and download the update package. You will need to have the lens mounted on a camera and the camera connected to a Mac or PC. Full install instructions are provided after you click on the Mac or PC download link buttons.