Specs

11 elements in 9 groups. Close focus, approx. 11' or 3.8m.  f/2.8- f/16

This is a BIG lens, approx, 4800g with hood. (but not carry case) 45cm long and 17cm wide at lens. Dont believe Lowepro when they say a NatureTrekker takes a 400 2.8 Not this one that's for sure! Yes it goes, just, but not comfortably, zip is strained, At least it wont fit with Lens cover, which sort of defeats the object (ive) (excuse the pun.). Another review by Moose Peterson.

Performance

Ultra fast, and when used with D2H or D1 gives a 600mm f2.8 :))))))) brilliant for wildlife, birding etc, when combined with TC1.4 or TC2.0 we are talking 840 f/4 or a 1200mm F/5.6!!!!!!!! Very Sharrrrrp! Check out shot below, taken wide open with TC1.4 (or 560mm f/4) late evening on Fuji Velvia, you decide!

So far after 2 trips to Africa I am sold on this, search time is just about nonexistent in reasonable light, together with the ability to manually override at a touch its amazing. I love it, I love it!!. However when it comes to getting there with it,  I hate it, I hate it , Airlines see me approaching and you can see them calculating my body weight when carrying this, I generally say will store under my seat, as at $7500 there is no way this baby is going in the hold!. Sometimes this causes problems, others not, its not the airline, rather the mood of the person you are dealing with on the day. Filters are drop in variety, easy to use, although my Polarizer did manage to fall apart after 4 days in a very shaky landrover in Kenya. Same size as for 200/300/500/600 AF-S models which saves money, (unusual for Nikon.) I sold my soul for this, after having realized that the 300mm was just not enough for serious wildlife photography, especially birds, and this together with the converters gives far more flexibility than any other combination.  Having said that, I think bang for buck, this is far superior to the 300mm, and worth the extra. (did I really say that!!)On cost check out last para of 300mm review for some astounding facts on Nikon pricing, and how and where to buy your gear.