Yes, I’m retracing my routes with this one was well…  I originally bought the siggy 12-24mm when I had my 10D knowing a 1Dii was in my near future…  It’s the go to wide prime for the 1 series IMHO because that body needs full frame lenses and the 17-40 and 16-35 lose enough of their width it needs wider IMHO.  Then I went FF and LOVED this lens on my 5D, but for some reason I got on a sharpness kick and replaced it with the sharper 17-40…  Well now I’ve realized I only need “sharp enough” lenses, not “pixel peep at 100% perfectly sharp” lenses so I’m trying it out again as 12mm on full frame is a hell of a lens.  I’m also curious to see how the whole filter thing works out as I “proved” cokin X-pros work but never really used them…  Now I’ve been shooting a ton of landscapes, and more than once I’ve wanted wider than 16 or 17 could get me….  So here I am trying it again.  It’s also interesting to me because I sold this lens back in the begining of my “in the black” camera gear budget (meaning I’m not spending any money out of pocket on gear, it’s all from sales of images (which is nill) or sales/trades of gear)…  I sold it to fund the 17-40 and 15mm FE.  Well since then I’ve sold the 17-40, gone to a 16-35II, went back to the 17-40, then to the 20-35, then to the 16-35 I, and now back to a 17-40 AND 12-24, but with all the trades and deals I’ve worked out, I’ve basically added this to my bag for free!