Originally posted by rawr I think the patent and other material people have consulted indicate that it was designed to cover the FF image circle. No-one makes APS-C specific super-telephotos, not even Sigma or Tamron, AFAIK.
According to the PF forum
review the vignette is 1.3 stops @ f/5.6, not so bad @ f/8 and acceptable at f/11. The conclusion was that it could not be called a 'FF' lens but would likely give acceptable results.
I believe it was actually designed as APS-C only. Remember this lens was worked up during Hoya years probably designed even before then. Left to languish and then dusted off by Ricoh. At that time Pentax was focused 100% on APS-C, still saying that until maybe 2012 or so.
At any rate, you are correct that it will give at least some good result on FF.
I wonder (assuming there will actually be a Pentax FF) how they will straighten out the naming conventions so it makes sense to poor buyers?
Clerk: Well this is a DFA lens and it will work great on your new $2,500 FF camera.
Customer: What about this DA lens?
Clerk: Oh, yes that DA lens will work just fine!
Customer: And this one here will work then?
Clerk: Oh, no that DA lens will not work.
Customer: Huh?