I have no interest in this Zeiss lens however. TDP even mentions the Zeiss some has coma, not ideal for stars. I heard the Samyang has one up in this regard.
Actually, the Zeiss has very little coma, except in the extreme corners. Even then, it's not much. That's the main reason I bought the Zeiss (for star pics), after hiring and testing a couple of other lenses (a Canon 24mm f1.4 and a Zeiss 21mm). Plus the hard infinity stop makes distance shooting easy, day or night.
5D mk3 with grip, 300 f4 L, 100 IS Macro L, 50 f1.4, 50 f1.8, 40 f2.8 pancake, 35 f2, 1.4x TC III, Zeiss 15mm f2.8, 24 f1.4 L
580EX II, MT-24EX Macro Flash
EF 12mm and 25mm II Extension tubes