I have seen over and over the excellent results from Pixel shift files, and had been waiting to get out at night when I could try the astrotracker feature, needless to say, at least on the 15-30 @ 15mm, the feature appears to be a bit broken at least on my camera.
At 2 minutes, which is not even half the total time which can be used (5 minutes is the total), I found that the Astrotracker can only track well in the center of a shot and as you move out towards the edges of the image, you will start to see traditional star trails, to full 2 minute trails at the edge. And the Milky way is not tracked correctly (since there are trails) and it's blurred against the trails.
I have attached some screen shots from C1, the image on the left is a 25 second Pixel shift shot and the one on the right is from a 2 minute Astrotracker shot. As you can see, the right edge is basically not captured at all. Not sure if this is due to the 15mm lens? which is so is a huge surprise as most landscape work involving the M way is going to use a ultra wide lens, 14mm to 20mm. My GPS was calibrated, (you have to do a calibration each time anyway as prompted) and it actually correlated very close to what my Garmin showed, so don't think that was the issue. Anyway, will try again, but I worked up several shots during the evening and all showed the same thing.
Here are a few screen shots.
Image on right is a pixel shift (taken to see if noise levels would be lower) and image on right is 2 minute astrotracker
Image 1 shows a side by side 25 sec on left and 2 min on right, basically almost full star trails on the astro tracking image
Image 2 show a crop from dead center and if anything the astro tracker shot is a bit out of focus
Image 3 shows a crop from top middle, and here the stars are sharp, and no trails
Image 4 shows full images, mainly to show the dark color band toward top of all files, this appears on all images taken in either astro tracker or Pixel shift @ 25", did not try traditional stacking to see if band still shows. This is bigger show stopper than anything as it has to be corrected each time. in the side by sides, I have already worked on the band so it's not as evident.
Also note that the Milky way is blurred in the 1st screen shot, so basically astro tracker failed 100% here. GPS was fully calibrated and confirmed to be so.
Images worked in Capture One.