Yeah or The f/4 is about half the weight of the 2.8 (700g vs 1350g  there is a different coating Richard. on the f4  It has a calcium flourite lens element (the 2.8 does not...has UD instead).

Danny O'Byrne  http://www.digitalartzone.co.uk/

"All the technique in the world doesn't compensate for the inability to notice" Eliott Erwitt