Opticallimits

;-)

So the L USM IS has a couple of weak spots after all.

Is native vignetting among them? :-)

The corners aren't perfect at the long end actually

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And bokeh highlights are a bit meh

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I'm beginning to doubt that this will be a 4* lens.

Well, we aren't at school where nothing less than 4 (of 5) would suffice.