The 85 1.8 doesn't suffer CA as much as the 1.2. I had it but sold to get the 1.2. Haven't used it for astro.
I'd be recommending the 135L. Have used it at last year's Qld Astrofest. Images/examples here with 5DII and 135L combo:
http://www.iceinspace.com.au/forum/s...d.php?t=124297
http://www.iceinspace.com.au/forum/s...d.php?t=123902
http://www.iceinspace.com.au/forum/s...d.php?t=123928
http://www.iceinspace.com.au/forum/s...d.php?t=123833
For something around the 85-90mm FL mark, I'd be going with the Tamron 90mm macro lens. It's sharp and a great macro lens, too. It has curved aperture blades, so the diffraction spikes when stopped down aren't as prominent. See some of Nettie's images for examples, noting the star profiles:
http://www.iceinspace.com.au/forum/s...ghlight=tamron
http://www.iceinspace.com.au/forum/s...ghlight=tamron
http://www.iceinspace.com.au/forum/s...ghlight=tamron