i was looking pretty hard at the zeiss 25mmf2 also, but i found it's not really best at infinity. I read something alluding to that somewhere, i can't recall, but then later i do remember Roger at lensrentals mentioning it a few times. No doubt a very good lens, but astro work might not be in it's design brief. A search of the lensrental site should dig it up if your interested. i know i wasn't about to drop that amount of coin for a MF nonweather sealed f2 lens unless is was unrivaled.