I finally managed to get out to try a few quick snaps with the 17mm/4.0 Fisheye yesterday evening and this morning.
There is slight motion blur in this first one. I was walking backwards to keep the pony in frame, and I hadn't got around to trying out shake reduction settings yet. It turns out that the 15mm shake reduction setting works best, which makes sense as the fisheye projection gives the 17mm about the same field of view as a 15mm rectilinear. This one is de-fished using PT Lens:
This next one is also de-fished, which is how I'll probably be using the 17mm most of the time:
This last one has not been de-fished. The fisheye effect slightly exaggerates the tilt of the stone cross, but only slightly. Centuries of ponies rubbing up against it for a scratch have left it at quite an angle.
Overall first impressions: the colour rendering is slightly cold for a Tak, which I suspect might have something to do with the built-in UV filter. And it's a very contrasty lens, which I know is supposed to be a good thing, but personally I prefer a bit less contrast to give me a more malleable raw file. For the sharpness fans, you need to shoot at f/11 to get good corners even on APS-C. I'm looking forward to getting to know this lens better, and I think it might take some time before I really start understanding how to use it right.