I saw this lens recommended a lot for IR because it gave clean results, but I'm a little disappointed by it. It's not bad, by any stretch, but it doesn't seem quite as good as the newer 16-35mm f/4 IS version. If you look at the chats for these two lenses side-by-side they are actually very similar apart from the 17mm on this lens and when you look at the samples it appears more like lens flare than hotspot. Perhaps I need to do some more tests to see what is going on here. Although this is an 'L' lens it's not very sharp in the corners by modern standards, but the same is true of the 16-35 version. If, like me, you're coming to one of these older lenses for better IR performance on mirrorless, but you're used to the sharpness of newer mirrorless designs this will disappoint you in the corners.