[Brightcolours]

You can yell. Still does not change things....

 

Two simple questions, with two short answers.

 

1. Why is the 300mm f4E PF so remarkably short and light (same goes for the Canon 400mm f4 DO IS USM II)? 

Answer: Because of the use of the PF (DO) element.

 

2. Does the use of the PF/DO elements mean a whole lot of extra elements are needed to get rid of the aberrations?

Answer: No, one refractive element counters the CA. That is why such lenses have similar number of elements as modern tele lenses without DO/PF elements.

 

Since I am not allowed to use the 400mm f2.8E as measure, because you claim that the bigger aperture would mean more elements, an other 300mm f4 lens with IS group:

Nikkor AF-S 300mm f4E PF VR: 16 elements. Canon EF 300mm f4 L IS USM(pretty old design in its own right): 15 elements.

The increase in elements is pretty normal for modern tele prime design, and is not due to the use of the PF element. By the way. The 500mm f4 and 600mm f4 lenses with IS also have 16 elements. Pretty normal number for modern tele design. Not much to do with the inclusion of DO/PF.

 

Why do both Nikon and Canon use such elements? Only to make such a short and lighter tele possible.