Back in late 2010 when I purchased my 300 f2.8 VRII for birding and wildlife, I was considering other lenses around this focal length in my purchase decision, like the 200-400 f4 VRII and the 400 f2.8G VRII. The 400 f2.8G VRII was quickly dismissed due to the weight, size, front heaviness, silly placement of the tripod mount and the two piece lenshood. It was down to the 200-400 and the 300 f2.8, the 300 f2.8 won out due to it being f2.8 and it's stunning IQ and sharpness. Part of the decision making process was that the lens needed to be easily portable and also it needed to be versatile, ie that it can use TC's to allow for different focal lengths. The 300 fitted the criteria perfectly and I couldn't have been happier with my decision.
After 18 months of use with the 300, I was lucky enough to be able to pick up a pristine condition 500 f4 VR for a very reasonable price from a friend that was getting too old to cart it around, he was 82 at the time! The 500 had better IQ than the 300 when the 300 was paired with either the 1.7x TCII or the 2x TCIII and the 500 was excellent with the 1.4x TCII for a very useable 700 f5.6 and thus became my preferred long birding lens. The 300 was still the king under 500mm even with the 1.4x TCIII attached to the 300. However, when Nikon introduced the new 400 f2.8E FL VR mid last year, they had fixed all the issues that I thought let it down on the original 400 VR, ie they made it lighter, it was now well balanced rather than front heavy, the tripod mount was moved to a more balanced position and it now has a one piece hood, making it a very portable lens. In fact, the new 400 was very similar in everyway to the 500 in size, weight, balance, handling, tripod mount position and lens hood. After a bit of consternation, saving money and talking to a few owners of this fabulous lens, I decided to take the plunge and I ended up getting the new 400 f2.8E FL VR. One of the people I had contacted in regards to this lens and helped talk me into it was Tony Oaten or Antonoat from this forum. Thank you Tony!
All I can say is that this lens exceeded all my expectations as to how good a lens can be for overall IQ and performance. AF is super fast and accurate, it is just stupid sharp giving stunning detail and has outstanding bokeh. It takes all 3 TC's with minimal image quality loss, for a 400 f2.8 bare, a 560mm f4 with the 1.4x TCII or TCII, a 680mm f4.8 with the 1.7x TCII and an 800mm f5.6 with the 2x TCIII. As a guide for using TC's my rough guide for AF speed loss and IQ degredation would be about:
With the 1.4x TCIII, AF loses about 15% AF speed and about 10% in overall IQ.
With the 1.7x TCII, AF loses about 25% AF speed and about 20% in overall IQ.
With the 2x TCIII, AF loses about 35% AF speed and about 20% in overall IQ.
These are not measured quantities, just my seat of the pants thoughts after 3.5 months of use and probably close to about 10,000 photos!
I believe the 400 f2.8E FL VR is now the most versatile birding/wildlife lens in the Nikon lineup. Yes, the old 400 f2.8G was very versatile as well as it also took the 3 TC's probably just as well, but the fact that it was a bit unwieldy and front heavy, weighed almost a Kg more and the two piece lens hood made it less of a portable lens. I can fit the new 400 in my backpack with quite a few other lenses, this would not have been possible with the old 400. Just my opinion and my requirements.
Some may have seen these on other forums but for those that haven't, here are some examples. These are out in the field examples, so, real world photos as the lens would be used on a day to day basis:
Best viewed at their original 1800x1200 pixel size.
D810 + 400 f2.8E FL VR, f3.5, 1/1600sec, ISO224, handheld.
100% crop of above:
The lens has beautiful bokeh
D810 + 400 f2.8E FL VR bare, f4, 1/200sec, ISO449, handheld.
D810 + 400 f2.8E FL VR, f8, 1/400sec, ISO449 handheld, cropped about 50%!
D810 + 400 f2.8E FL VR + 1.4x TCIII (560mm f4), f8, 1/1250sec, ISO504 handheld, cropped about 15%
D810 + 400 f2.8E FL VR + 1.7x TCII (680mm f4.8 ), f6.3, 1/3200sec, ISO898, handheld. Cropped about 25%
D810 + 400 f2.8E FL VR + 1.7x TCII (680mm f4.8 ), f5.6, 1/800sec, ISO64, handheld cropped about 30%.
D810 + 400 f2.8E FL VR + 2x TCIII (800mm f5.6), f8, 1/1600sec, ISO635, monopod. Cropped about 20% for compositional purposes
D810 + 400 f2.8E FL VR + 2x TCIII (800mm f5.6), f8, 1/1600sec, ISO400, handheld.
Crop to what I was after:
100% crop showing the incredible detail even with the 2x TCIII hand held with AF tracking.
More examples at my site - with and without:
http://www.pbase.com/lance_b/nikon_400_f28