It isn't like I don't have other wide-angle lenses, but this baby has less distortion and almost the same field of view of my 16mm fisheye, and is a full stop faster than my 10-22 zoom - very important for night-time shots, in particular the time-lapse shots I've been shooting lately. This week, with the University shut down, I picked up some extra shifts on Kitt Peak, and had a little time for some test shots after my duties there.
This time of year Orion rises early, but once clear of the horizon it is difficult to get into the field of view with a dome or other item of interest. But with the wide-angle, it is easy to do so, and with the fast aperture, 30 or 45 seconds at ISO 1600 records enough light to even get some shadow details in the near blackness, and expose short enough to not get too much star trailing.
The image at left here is off the west side of Kitt Peak showing the western sky. Visible in the 60 second exposure is the Summer Milky way to the right, and the glow of the Zodiacal light to the left. Besides the lights of Sells (the capital of the Tohono O'odham reservation), the faint light domes of distant cities can be seen. Just upper right of Sells is the US/Mexico border town of Lukeville/Sonoita. The brighter light domes of Why/Ajo is to the right. I've not identified the light domes into Mexico, but I'm amazed at how well the light domes show up from so far away given how clear the skies were... A couple nights later we had some thin clouds after our observing session and I took a few frames of them moving through the rising Big Dipper and Polaris (to left). This was only 30 second exposure...
Finally a daytime shot of the Visitor Center at the Observatory. Note how the straight edges of the building remain mostly straight, unlike what you would get in most ultrawides or fisheye lenses. I'm mostly happy with the lens - I need to do some tracked shots to test it's ultimate sharpness, but for the money seems to be a good value.