[davidmanze]

BC mentioned the Nikon PF lenses already: very compact, too, but just one stop slower than their super-tele siblings. However, not really cheap, especially not the 500 PF.

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  A friend has the Nikkor PF 500mm F5.6 VR  ........  

" an amazingly compact and lightweight lens" ..... looking much like a 300mm F4 ....... uncannily so ..... almost tiny.

..... incredibly sharp with rock solid  VR ...... even the bokeh is excellent  .... in fact it would fool many into thinking the images are from the 500mm F4E ..... it's that good !!
  It is however, 4,000 euros and hen's teeth rare ........ but worth every penny .... as it will hold it's value forever .... (S/H copies were selling for more than new)

  Nikon's patented 600mm F5.6 version is promised at some time ..... (come on Nikon!)

  ..... the 500 PF passed almost unnoticed here in OL land .......

One of yesterdays golden hour shots at F4.5 ...... from the 600mm E

https://www.flickr.com/photos/124690178@N08/49993070031/in/dateposted-public/