Chuck Vaughn (in another post) has stated that the prism from the
OAG will cast a shadow on a medium format frame, and that would appear to be
the case. It may take a fair amount of additional work to get
going.
Even if that is the case and the shadow will be too dark to remove
digitally, there will still be a huge increase in coverage over the 35mm
coverage area. Cropping of the vignetted area will still leave a large piece
of sky on the image.
Bobby Middleton