Excellent, but...

AdamT wrote:

can cause blurry edges)

Yup, there’s a fair amount of field curvature inherent in the 15-45’s design (it’ll be present in all copies). And you’ll see moderate mustache distortion at the wide end. Canon’s DLO corrections help with these, but good practices in the field (as you mention) also help.

The 15-40s curvature seems to run in reverse, where it pushes away from you rather than the more usual bending towards so the focus deep trick doesn`t work .. the issue is less at the long end ..

I've always focused shallow (basically 1/3 into the scene) for greatest DOF. Whenever possible I like to compose with a nice foreground object (when at very short focal lengths), so I keep an eye on where infinity ends up as I'm focusing as closely as possible.

The 15-45’s big fault is that darn decentering that folks should look for when they get a new lens,

and the prob there is that the lens isn`t big enough for the IS System and throws up random blurry edges because the IS has moved out of range at the time of shot ,,,,

That I haven't seen. I'll have to watch for it!

I suggest a row of houses or shops (Test charts & brick walls are useless unless that`s all you want to shoot because decentering / Curvature is worse at normal distances) and take multiple shots wideopen and at F5.6 then if there`s a regular soft side, shoot it upside down to see if the side swaps place when the image is right way up

I only use test charts for resolution. Brick walls work great. Decentering is very easy to diagnose.

mold/jig was at fault, and Canon should have been tossing way more of these sub-par lenses during their QC process.

QC process? are you kidding - LOL

R2