[Klaus]

Outstanding MTFs it seems:

 

http://www.usa.canon.com/cusa/consumer/p..._is_ii_usm

[Brightcolours]

Yeah, that looks like an awesome lens. For an unreachable price. It gained a little weight compared to the 1st iteration: 

2.1 kg vs. 1.9 kg for the old 400mm f4 DO. Must be a heavy extra element (17 elements in 13 groups for the old lens, 18 elements in 12 groups for the new design). No lens construction diagram for the new version available yet.

[Rover]

The price makes me want to



Seriously, this is nuts. 

[Brightcolours]

This explains the extra weight:

400mm f4 DO:



Orange = DO element

 

400mm f4 DO II:



Yellow = DO element

Dark green = UD element

Light green = ground aspherical element

 

Overall, the amount of glass has increased.

 

About the price, yes it is very high. But the big ground aspherical element and the double glued DO element have very high production costs, though.