Stone - You need a technically-minded person to explain that, which I'm not. But, roughly speaking, although the Mamiya 140mm doesn't get in any closer to your subject than any other lens for the same system, it does give a sharper focus as well as a softer transition to out of focus areas - or so I read. I'd be happy for someone else who knows what they are talking about to chime in...all I know is that it gives a nicer (the best word I can think of right now) image than any other lens I have.