Quarter-plate is 3 1/4" x 4 1/4", but the camera in the picture looks smaller than that (and I don't think Voigtlaender ever made plate cameras in inch sizes; their equivalent would have been 9x12). The lens is a 105mm, right?
6.5x9 used to be a fairly normal plate-camera size; I've got a Kodak Recomar in that size (which is why I'm interested in this particular detail; the backs are interchangeable between Kodak/Nagels and Voigtlaenders). The more I look, the more I think that's what it is, and the back (Rada, it looks like?) gives you 6x9 format on what's nominally a 6.5x9 camera.
Tell you what---can you measure the width of the flanges on the rollfilm back, and I'll compare measurements with my 6.5x9 back when I get home this evening? Sorry to be a pain, but it'll either fit or it won't...
Thanks
-NT