I am in the market for a Mamiya C330, and I want to use it with a prism, as opposed to looking down through the standard viewing hood. I would like the image to be upright, and not laterally reversed. What is the difference between the Mamiya prisims and the Mamiya Porroflex finders, which I see advertised on eBay? From what I can see from the pictures which accompany most auctions, the prism's eyepiece seems to be in the centre, and the Porroflex's eyepiece is offset to the left. Are there any other optical differences, or any other recommendations from Mamiya owners? I used the predecessors of the 330, the C3 and the C33, many years ago, and have always had a hankering for one. Any information on this subject would be greatly appreciated!