Actually the 100/2.8 does barely cover 3x4, at least at portrait/near-portrait distances. The 50mm, on the other hand, falls a little short.

http://www.flickr.com/search/?w=8892...olaroid&m=text
http://www.flickr.com/search/?w=8892...FP-100C&m=text

I can take a few more sample shots if you're interested