The bane of night photography of subject matter like the Milkyway, or just a nice star scape is coma. Coma tends to create a butterfly wing aberration on the stars towards the edge of the frame and is not really something you can correct in post as you are dealing with thousands of stars.
I have tried many of the nikkor mount 1.4 and 1.8 wides.
The Nikon 24mm 1.4, albeit a wonderful lens for landscapes, it's plagued by extreme coma (I found it on mine even at F2.8) and at F 1.4 and 1.8 the butterfly wings look really bad. I was a bit surprised to find this, but now with a better understanding of coma, you can easily see it on the corners in a daylight shot also.
The Nikon 24mm 1.8, is lighter, and seems to have more plastic, but it has less coma. I still have this lens and have had good night results with it at F2.2 and sometimes F2.0, depending on the angle to the sky. For regular star trail work, this is a great lens, as it does not flare as bad as others.
Rokinon 24mm 1.4, is not bad, but will pick up really bad flare if you are working around a building or anything that has artificial light. It has a huge amount of play in the focus ring, (just like the 14mm Rokinon) and can be hard to dial in at night. As for Coma, I have used it at F 2.0 with good success.
These are not as wide as I prefer to go as I find often I am looking for 14mm.
The Rokinon 14mm is a wonder both for image quality and price. At F2.8 it displays almost no coma and mine is very sharp at infinity to the edges. There is a pretty good sample variation with this lens however.
The Nikon 14-24, is still my main go to night lens, (I do more star trail work than Milkyway). Mine is very sharp at infinity and F2.8, has almost no vignetting and no coma. It's really an amazing lens, but it is a nightmare for flare as any light coming in from the side will create a horrible flare issue.
The Zeiss 18mm F3.5 is not bad, it has no coma at F3.5 but will vignette pretty harshly. The vignetting will easily correct in post, (LR). This is my sharpest wide lens for the stars, sky, etc. but it does not have a good hyper focal range at F3.5, so elements in your image that are close in tend to be out of focus. For Milkyway work, you can easily bracket this and if you stack for star trails, again you can bracket . I am always impressed with just how sharp the trails are to the edge of the frame with this lens. It's light weight and compact, when compared to the the 15mm and 21mm Zeiss.
I briefly used the Zeiss 15mm, but I found it to display a enlongated coma issue wide open and it's a very heavy, expensive lens just to use for for night work. The 14mm Rokinon I feel can deliver pretty close results to this lens wide open, without coma.
I had high high hopes that the Sigma 24mm 1.4 art would be coma free, however all the tests I have seen of it show it to have very extreme coma, possibly worse than the Nikon 24mm 1.4 wide open. So I passed on this one.
The Sigma 35mm Art 1.4 is coma free wide open. There has been a lot written about this lens and it's total lack of coma. A wonder of a lens. It's not wide enough for most of the work I do however but I have it for when I can get out west to the wide open spaces.
There was a nice write up over on LuLa about the D810A. After reading through it, I am tempted if Nikon gets the price point down a bit. Or maybe pick up a used one in a year or so. It's a very clean camera, even in the extreme high iso ranges, per this review and the IR filter seems not to really put a huge issue on daytime work. There is some slight cast, but nothing like the cast I had expected. The D810A also has a true intervalometer, that does have it's own timer, thus you can use it past 30 seconds, (something that cannot be done on the D810 but could be if Nikon wanted to). You can find the review here:
https://luminous-landscape.com/nikon-d810a-review-landscape-astrophotography/
Adam has a very interesting workflow, that involves stacking for the Milkyway, something I have not tried before, which allows you to use a much higher iso and then remove the trails that would be there since you are stacking.
This is an article I wrote for getdpi last year on star trail work, but in it I also talk about some of my findings about Milkyway or star scape work.
http://photosofarkansas.com/2014/09/23/092314-using-stacking-for-better-night-photography-results/
It is definitely a different form of photography, one that gives me a lot of pleasure, but has not been commercially successful for me. :banghead:
Paul