I like the old Nikon F accessory boxes with the hand written "product Number"'s on them. The Field Previewer is Product Number "2305". Looks to be the same box as the N->F adapter. It's fun to come across some of that early stuff, but I've always stumbled into them for cheap. I can't complain about not finding a 2.1cm F4 S-mount for cheap after getting the two M's. That's the part of collecting that I find is fun, like a treasure hunt.