With the R-D1's 1.53x crop factor, you will either need a different finder or you'll need to mask off the finder that lens comes with so that it shows a 22.5mm field of view instead of 15mm. I'm thinking about getting a 15/4.5 myself and asked about the finder issue in another thread (
here).
A few things:
1) As Sean explains in his wide-lenses review on Luminous Landscape (
here), the 15/4.5 vignettes quite badly on the R-D1. I'm prepared to live with that; you might not be.
2) Unless you need something else from B&H in the same order, would you consider buying from Stephen Gandy at cameraquest.com? Buying from him is a nice reward for the immense time he puts into one of the most informative RF sites around -- and you'll even save $4.95 versus B&H.
3) Gandy stocks the best viewfinder for the 15/4.5 on an R-D1, the Cosina Voigtlander 15D (D indicating that it's designed for digital -- that is, it offers a 22.5mm field of view instead). Unfortunately, that finder is $175, and the screwmount-to-M adapter you'll need to mount the lens is another $55. Instead, as the above-linked thread suggests, consider the $128 finder for the 25/4, which is apparently a good approximation of what you need (better at infinity, a little too tight at close focus) or buy the 25/4 lens as well, which comes with the finder for $245. Then you'll have an extra lens, although you'll need another external viewfinder for that one (does it never end?) unless you don't wear glasses. If you're spectacle-free, apparently the outside edges of the R-D1's built-in finder, outside the 28mm framelines, work OK for the 25/4. No matter what viewfinder you go with, you'll need that screw-to-M adapter.
