My RF native kit to date has consisted of the 16mm f/2.8 and the 50mm f/1.8, plus sundry adapted lenses. While I'm extremely pleased with the performance of both those lenses, I did recently find that for landscape-y type scenes I was doing a bit more lens swapping than ideal.
So, after seeing that someone on flickr had some good IR results with the 15-30, I decided to give it a shot. (First time using a zoom lens in like a decade, I think.)
Initial impressions are that it's usable, but not ideal. There's a hotspot that kicks in at f/11-ish. It's somewhat dependent on the scene, so I suspect a lens hood might help (I have one on order.) Overall contrast is a little low, which is no big deal, and at the wide end, the edges can get a bit funky, which is not uncommon for IR.
(BTW, from what I could tell by trolling google, it looks like the 14-35 f/4 L has somewhat worse hotspot performance.)
Here's a hotspot comparison at f/8, 11, 16
