[QUOTE="cuthbert, post: 2182015, member: 71325"
I want to explore the capabilities of very wide angles (not fisheyes) more.[/QUOTE]
You may wish to try an 18mm on a 35mm camera if you ever get the chance, there was a rather unexpected difference from 20mm to 18mm, which surprised me around 25 years ago when I picked up my 18mm.
My version is a Sigma and compared directly alongside the Nikkor equivalent, it is slightly softer, but for the price I paid, I've never regretted it.
Mick.