I use the Canon EF 85mm f/1.2L II USM as my main astrophotography lens where that f/1.2 aperture is really valuable. I guess this lens is more often found on full-frame cameras in the studio but lacking both here is a sequence of shots illustrating resolution at all of the available f-numbers. Click on any of the thumbnails to see the associated full sized (4MB) "Large Fine" JPEG as delivered from the camera with no post-processing.
Camera: EOS 40D, ISO: 100, White Balance: Daylight, Picture Style: Landscape, Tone Curve: Standard, Contrast: 0, Sharpness: 4, Color saturation: 0, Color tone: 0, Highlight tone priority: No.
To show just how scary the shallow depth of field of this lens can be here is a 33% crop of the first shot I ever took with it. This at f/1.2 and, from memory, at around 1.5m (closest focus distance for this lens is about a metre). The distance from the eyes to the end of his nose is just 11cm.
Finally, here's a composite of two images, each of which was produced by combining multiple exposures, all at f/1.2. This post refers. Northern hemisphere observers may recognise the constellation of Orion: