Paul,
I notice you use a Nikon 14-35 2.8 zoom. I have the 16-35 f4 and a 20mm 2.8 prime. I"m wondering if it might be better to use the prime lens at f4 rather than the zoom at f4? I know I just have to try it myself. Also, what about focus stacking. I see that you did not need it in your Haw Creek example.
I have not used the 20mm F2.8, but have the the 20mm 1.8 and have used it on a few night shoots. The 14-24 is still my main lens to use since in my locations, I often find 14mm is really needed for the best view of the sky. The 14-24 even at F 2.8 has almost no coma, at least mine doesn't and for night work that is a big plus. I find that at F3.2 to 3.5 I can easily get a good shot from around 11 feet to full infinity, the foreground may be a bit soft, but it's a nigh shot. In the Haw Creek example in my article, the rocks in the foreground were about 10 feet away from where I had my tripod.
The 20mm 1.4 still has quite a bit of coma in the F1.4 to F2.8 range, but it starts to get manageable my F3.5. However I can get a wider view with no vignetting (almost) with the 14-24, so I always lead off with it. The 14-24's only real issue is flare, and you really have to watch where the moon is in the sky as even with the moon well out of the frame, the 14-24 @ 14mm will pull flare. The flare moves with each frame as the moon location is moving also. This can add a lot of extra work in post processing. I always have a flare buster with me to help block the flare. The 20mm 1.8 will flare but not as bad as the 14-24.
In regards to focus stacking, I never really have considered that for this type of work, instead attempting to set up the shot so that the hyperlocal range of the lens covers me. The biggest issue with a stack solution is movement of the camera. Even the slightest touch can move the camera enough that you will a misalignment when you run the stack modes. This can be fixed sometimes if you try aligning the layers before running the stack modes, but it won't always get the issue fixed. At night, I tend to set the focus and then never move it again.
There is one solution to help, and that is take a final series of segments at a higher aperture, say F6.3 or so. This will help get the landscape portions of the image in a bit better focus, you just extend the time of the last few segments. This will more than likely overexpose the sky/stars but for these shots, I am only looking to improve on my landscape portions, not the sky. As I am using an external intervalometer MC-36, it's very easy to reset the overall exposure time without moving the camera.
I have not used the 16-35 F4 at night, but I did use it outdoors and found the corners quite a bit soft until F6.3, so for night work, I ruled it out since I felt it would be way too soft at F4.
The other huge disappointing lens from Nikon is their very expensive 24 1.4. This lens has more coma aberrations that the 20mm 1.8, and really can't be used for much night shots unless you are in the F4 or higher range. As I have come to discover really no one can make a fast wide @ 24mm without coma, at least from Sigma, Nikon or Canon. Coma is by far the most destructive form of aberration that you have to fight in nigh photography, especially if you working a Milky Way shot of star freeze. In both of these, you need to be as wide open as you can go, without introducing coma. The Sigma 35mm F1.4 is amazing in this regard, sadly in my locations, it's just not wide enough to work with, however if I was out west I would own one for sure.
Paul
