So I'm looking into a new lens in the near future hopefully; an 18-180mm probably. I was considering adding a teleconverter to the mix to make the lens even more worthwhile. But I'm not exactly sure how they work. I know you snap it on behind the lens to increase the focal length, but does that magnify everything you shoot, or just extend your maximum focal length? also are there any drawbacks to using a teleconverter?