Thanks, that sounds like what I was expecting, its going to be used with a custom mask which blocks 33% on each side of the frame resulting in simulating a 50% crop of the image (Like adding a 2x TC) for compositional purposes, hopefully allowing me to compose as if I am looking through a normal viewfinder and not seeing a) a small frame and b) lots of black.
which can be done to an 80mp file, while still having a highly usable 40mp file still while letting me technically double my focal length so my 300 + 2x TC becomes 300 + 2x + 2x. Of course the files will still be full resolution, but it makes things a lot easier when composing obviously.
Any alternate suggestions to the magnifier made by Mamiya?