The sharpest lens I have ever used .....

[JTPhotography]

Samyang 135 f2 manual focus. Wow is all I can say. Here is a 100 percent unedited crop shot at f2 from the edge of the frame on a Nikon d800e.

 

[IronMaskDuval]

Have you used nikon 60/2. That's a wow wow.

 

[Solarflare]

Shall we make a list of lenses that are famous for sharpness

My most likely candidate (would love to own it but I dont) would be:

Zeiss Makro Planar T* 2.0/100mm ZF.2 - used by Nasa for recording rocket starts because when they tested it showed more details than any other lens

P.s.: Though I'm fairly sure NASA choose the ZF version, instead of ZF.2, because CPU contacts wont do them any good