Here's a scenario which I'm sad to say hasn't happened to me. Your long lost Uncle who happens to be very rich finally contacts you and offers to buy you any single piece of photographic equipment you want, any cost. But stipulates it must fit into what you already have, only be a single item, you can't sell, swap or give it away or use it to replace something then sell that item, and you must use it. What would you pick? Think I'd get the Ziess Batis 18mm f2.8 lens.