Announced last week, the Zeiss Apo Sonnar T* 1700 mm F4 lens is the world's largest telephoto lens (for civilian purposes). According to a Carl Zeiss press release, the Apo Sonar T* 4/1700 was custom developed "for a customer with very high demands and a special interest in long distance wildlife photography." It weighs 564 pounds, consists of 15 optical elements in 13 groups, and is compatible with a Hasselblad 6x6 medium format camera.
From the excellent Digital Photography Review site:
The price hasn't been disclosed (although we've heard rumours) nor has the private owner, although some of the text on the lens is in Arabic and it carries a 'State of Qatar' emblem.Link (via Laughing Squid)