I just bought a D3200 and the 55-200mm lens. The camera came with an extender sort of thing which is supposed to attach to the end of one or both lenses. The extender piece, which is just a black ring and about an inch wide, goes onto the end of the lense. Can someone tell me what it is for? Do I need to use it to take normal pictures or is for certain types of pictures. Thanks for any help