Honestly Wolfgang I would be waiting until you get your D500 body before buying new lenses as the D500 has very good high ISO performance (might work well with the Tokina 10-17mm). I had a quick look and the Olympus 12mm f2 which has an AOV of 84° which is the same as the Tokina 11-16mm f2.8 @ 16mm. So if you do want a wide angle rectangular DX lens with great performance with the same angle of view as your Olympus 12mm the Tokina 11-16mm would be worth looking at. I have the lens which I mainly use for landscapes and its a simply a great lens for that purpose. I tried it underwater a few weeks ago and was very impressed with its performace but at the end of the day it wasnt wide enough for my style of shooting but it might suit yours much more as you need that extra reach so to speak.