I was chatting with a guy in St. Louis who's initials are SF. He's a very experienced pro-photographer. He was telling me about some kind of polaroid film that gives you a positive AND a negative. He said the negatives yielded by this film are excellent...nice and big and can be used to create really cool prints. Is anyone familiar with this technique? And, am I referring to it correctly? I don't think this film is available anymore but maybe some of you have used it.