daniel buck
Established
Kind of OT (since the OP wants to know about performance specifically at f/8 and infinity): I've read and re-read that thread several times, and the funny thing is, it seems to me that it says two things at the same time. The Ultron is pretty good (sample-dependent), good enough to possibly not need/want anything else. But the cron isn't just added sharpness in the corners. It is 'better' OOF, better microcontrast, better color, etc etc, that adds up to a subjective look: "skin looks like it's glowing from inside".
On the other hand, there are people like Tom A. and Sean Reid who have found a certain subjective magic in the Ultron, particularly wide open and close in.
And this review is on an M8, not an M9. An M9 sees more of the outsides of the lens coverage, the worst area of the lens. on an M8, the Ultron and summicron may be a lot less distinguishable between each other. But on my M9 in the corners and sides the summicron is quite alot better.
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