Tokina announced a 400 mm mirror lens which comes with a 2x TC for equivalent reach like a 1600 mm lens! The weight of the lens itself seems to be 355 g, what it would be with the whole kit ()including mount adapter) I do not know.
Niels
Tokina - SZX SUPER TELE 400mm F8 Reflex MF & 2X EXTENDER KIT
tokinalens.com