Hey Brandon,
This looks really cool. Scorpius Arch is one I still need to get out to.
Overall this looks really good. The K1 tracking won't in a sense be as good as a real tracker, but to be able to shoot for 90 secs (which is 3 times longer then normal) and at ISO 800 is really great. I personally wouldn't worry about the slight difference between it and a tripod mounted tracker.
As to the look of the sky, even if you had used a tripod mounted tracker the sky would essentially look the same unless you modify how you are processing. I have found when converting your images from Raw to edit in ACR that a very healthy dose of the DeHaze adjustment really helps darken the background sky while not brightening up and blowing out the bright areas (like a Contrast adjust might do). I would go anywhere from 40 to 100% DeHaze depending on the image. I used to use some intricate layer masking to do the same, but the DeHaze does essentially the same thing much simpler.
In the arch, had you simply forgotten to apply the mask to the arch hole? Because of movement when using an Tracker device you essentially take your ground layer, create a layer mask for all of the sky, then have your tracked night sky behind it and you slide it down behind until the blurry ground level on it disappears. So that's my one reason for not liking to use any kind of tracker, is I don't like altering my night sky by moving it to that degree. It's probably something I should get over.
For the ground, I think the brightness of it is fine. I might darken the very bottom of it just a little more just to have if you will a little bit of a vignette feel to help draw the eye then up to the arch. But the overall darkness is good. That's a hard feel to get right too. Because on one hand as Alan suggests you want it to feel like it's night time, but on the other hand it has to be bright enough to show detail or otherwise the details of the ground disappear and you might as well just eliminate the ground layer. So I like what you did, especially since other then the arch you didn't light paint, that's the natural light you worked with for the ground.
In the arch, I think I might clone out the light source on the bottom of it, and just leave the glow on the inside of the arch itself. Did you shoot any ground layer shots without it being lit up? I am not sure the arch really needs to be lit up, though I know everyone who shoots it has done it. And if I shot it I would do it too, but I would also shoot it without the light source just to compare when processing. The issue often with light sources in arches is to explain to the viewer were the light came from without using words. Most often it's because we see someone in the arch holding a light. Now that's quite the overdone and over used method. So an even softer light I think would be the key here. One that just gently lights up the arch inside but isn't so bright that you figure it's lit up by someone.
Anyway, lot's of talking by me here, and still I want to say that overall I like what you got here. I would love to see you redo the processing on this, not because this is bad, but I would love to see you use DeHaze for the sky and darken it and make that Milky Way pop, and then also to correct the layer mask for the arch and maybe tone down that light painting in the arch.
Next time you want to go out there, let me know.
