Nikon AF-S NIKKOR 400mm F2.8G ED VR（已停產）

1. Autofocus speed is just about instantaneous.
2. It is completely sharp across the entire field at every aperture. There is some minor light falloff at f/2.8, and none at f/4 and smaller. That's the only flaw I can find, and that's not a flaw.
3. There is no visible distortion.
4. None ghosts.
5. The 1.4x and 1.7x TC's work very well on this lens (560mm and 680mm respectively). The 2x TC, even the new one, I'm a little reluctant about. You'll note a drop in focus speed, for one thing. And surprisingly, my 1.7x gives me slightly better results than the new 2x. Still, if I absolutely needed 800mm, I'm not afraid of the TC-20E III, either. The combination is far better than the non-existent 800mm lens Nikon doesn't make yet.
4. focus ring was very smooth.

If the 400mm has a weakness, it's infinity focus. This seems typical of the whole Nikon exotic line, but while the 400mm is pretty good at infinity, it's just not as snappy as it is at 100 yards or 200 yards or wherever else you've focused that's not infinity. This isn't the same as the problem I note on the 200-400mm: the 400mm f/2.8G doesn't get weak on anything past 100 meters as the 200-400mm does. But it is slightly weaker at infinity than it is at 200 meters. Typically, though, you're not shooting at infinity.

400mm f/2.8G is, as far as I'm concerned, at the top of the Nikon exotics. The 200mm f/2, 300mm f/2.8, and 400mm f/2.8 are all superb lenses. Scrap that: beyond superb. Stunningly sharp and contrasty wide open, with only a hint of falloff in the corners. They're designed to be used at the widest aperture.

Here's the question that I usually get: which should I get, the 400mm, 500mm, or 600mm? From an acuity standpoint, the 400mm is the best of that bunch, and clearly so. The 400mm with the TC-14E is pretty darned close to the 600mm f/4 (disclaimer: I've only used Nikon NPS 600mm loaners; make of that what you will, but those lenses get used and abused by a lot of photographers, so I'm not sure I've seen the best the 600mm can produce). I tend to rule out the 600mm for all but the absolutely focal length obsessed (you know who you are, and you like little birdies ;~).

One final note: this review is of the latest and greatest version of the 400mm f/2.8. I've used all the predecessors (mostly through rentals), all the way back to the old AF-I version. The differences are subtle. The current version has a slightly more sophisticated VR system and Nano coating, and those can make a very small difference in some situations. But if you're looking for a bargain, any of the older AF-I or AF-S versions in excellent shape used may save you some money.

I've never been disappointed by the lens.