Hey guys, I've recently purchased a mamiya 645 pro TL, with standard 80mm lens, 120 back, power winder and non metered prism. My question is can I use the automatic exposure setting with my non metered prism? Or will I have to buy a metered one? Also if it is not possible for me to auto exposé my images.. Could you tell me a rough guide for shooting outside on a sunny day exposure wise? Thanks thanks thanks!