Yep, you can get adapters for most systems, but you do have to watch more modern systems using Autofocus as non of that will work when fitted to your NEX.
Mine is an Olympus OM setup - Zuiko 50mm f1.8 (£20 or so), Teleplus OP MC7 Macro Adapter and then the OM-m4/3 (in your case NEX) adapter. All manual focus of course, but suprisingly good results. (I've had supposedly good quality teleconverters before and they've all been naff)