Which is widest camera lens in the world?

It depends on what you mean by "widest". A fisheye lens has the widest field of view (180掳).

Widest in terms of widest aperture would go to the world's largest telescope -- since telescopes are really just large cameras. Currently the largest telescopes in the world are the two Keck Telescopes on Mauana Loa, Hawaii. Each one is 10 meters (32 feet) in diameter.

But the Kecks aren't really lenses; they use mirrors to focus the light. The largest lens-type telescope is at Yerkes Observatory in Williams Bay, Wisconsin. Its lens is 40 inches wide.