Yeah, I figured as much with the focal lengths re: "numbers". I was looking as well towards the 350mm or 500mm, but perhaps 500mm is a bit to extreme, but I work on a ship south bound to the Antarctic and I really like shooting icebergs and sometimes we just don't get that close to really big ones and 150mm just doesn't cut it in this case. a 100-400mm 4.5-5.6 L USM lens on a Canon 5D is great, but I no longer have a digital camera and want to get the same reach out of film. is 500mm too extreme in this case? It's a lot of lens and not exactly cheap.. I don't know anywhere even interstate where I could borrow a 500mm or even 350mm lens from.