I had one of these convertible lenses, and mostly used it at the 180mm non-converted focal length. I recall doing portraits on 4x5, though it's more of a 5x7 lens. I kicked myself for selling it, but the price listed here seems fair. Using it at 315mm does mean a lot more coverage, but the bellows I recall requiring somewhat more than one would expect of a 315mm lens, if for no other reason that you are conveniently removing the front cell, so the optical center is behind the lensboard.