Wow, when did you put in your order? I put mine in a few days ago; haven't received it yet.
is not THAT appealing to me. One, like mentioned above, we have equivalent lenses that have the same or even faster in 135 format.
E.g., the fastest 645 lens I know is Mamiya 80/1.9. That is the equivalent of a 53/1.2 on FF. Nice, but not unheard of.
And, to get a 645 image circle to fit a FF sensor, the reduction factor needs to be around 0.62, a lot more than the 0.71 of the current Speed Booster. Sounds like a bit more strain.
No, what I DO want, and do want now is basically the same exact optical formula (w/ reduciton factor of 0.71) that would mount to a Hasselblad (and other MF) mount AND the other end would mount to a yet-to-be-manufactured mirrorless DMF, OR, to something like the Hartblei H-cam and then a DMF back.
The 0.71 reduction factor will bring down a 56 * 56 format down to 39.5 * 39.5, which would ALMOST be perfect (but not quite) for the last square format DMF backs, e.g., CFV-16 (37 * 37). To get it down to exactly 37*37, we'd need a true 1.5x reducer (0.66x).
So with a relatively cheap square DMF back from several generations ago could suddenly act like a "near-full frame 6x6 back. Of course, if you have more dough to burn, you could get the bigger sensor DMFs and crop to square to get your true full fram digital 6x6 experience.
With the top of the line "full-frame" 645 backs, you'd be able to do 6x7 and almost 6x9, too! That would be awesome.