Is this the expected corner performance of Olympus M.Zuiko ED 75-300mm f4.8-6.7 II ?

Started 7 months ago | Questions thread
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milek
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Is this the expected corner performance of Olympus M.Zuiko ED 75-300mm f4.8-6.7 II ?
7 months ago

I just received Olympus M.Zuiko ED 75-300mm f4.8-6.7 II lens, refurbished, directly from Olympus USA.  I got it for a great price thanks to the recent spring sale, but I'm beginning to think that there may have been a reason why it was refurbished in the first place.

Top-left corner from a shot at 75mm, wide open.  This is not even the worst corner.

This was shot under controlled conditions (tripod, MF, IS off, anti-shock).  It's actually very good in the center, but corners are pretty soft, and they don't sharpen up until f/11 (and even then, only just).  Online reviews indicate that the lens should be tack-sharp corner-to-corner at this focal length, even wide open.  Did I get a bad copy of the lens?

I'm thinking of returning it, but I thought I would check first with others who have experience with this lens.

For reference, this is the full version of the above shot.

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