I have the 300 f/ 2.8 which by itself is excellent, but when the Mamiya 2X converter is added to the mix, the results are quite disappointing. I have shot with the mirror up and found modest image improvement but the combination still falls short of expectations and, for my purposes at least, mirror up is simply not an option. The better way to go might be to seek out a 500 APO. Having used this lens with film, I can tell you that this is easily the equal of the 300, i.e., very, very good. While I have no experience to offer with this one in digital formats, I can not imagine that you would be disappointed.