The lens is good at the 210mm length. You have to remove the front element to convert it to the 370 length (but as you point out the bellows draw required is more than 370mm because the lens nodal point now lies behind the lensboard - the 430 mm sounds about right). Performance isn't as good at the converted length since by removing the front element, some of the corrections designed into the lens are removed as well. Performance can be improved by using a strong monochromatic filter, which reduces chromatic aberrations. If it needs buying a longer monorail, it might be worth checking out other lenses as well. Alternatively, do not buy the longer monorail but try cobbling together an extension lensboard. I'm quite happy with this lens, even at the converted length but different folks have different demands. I even use it as a wide angle on my 8x10 (oddly enough, it covers, although specs say it shouldn't - the edges are soft but I don't need to splurge on a 210 SA). Good luck. DJ