Something odd with the Sony FE 28-70mm lens

I'm getting an edge softening on some pictures I've shot with the 28-70mm at 28mm. OK, I know what you're thinking, another crap Sony zoom. But it's not happening every time, even with the same shutter speed, aperture etc. It's also happening around the f/8 - f/11 mark. Plus as you can see below it's not the lens.

That's a perfectly acceptable result.

The difference? Top shot is hand-held with OSS on, bottom shot tripod mounted with OSS off. Top shot is 1/160th. sec. at f/10 by the way and the centre of the image is sharp.

I'm trying all sorts of things to track down what's causing this. Whether it's an OSS problem, shuttershock problem or a combination of both. It does happen on both my A7 and A7r. Plus I have had it before. My 18-55mm zoom on my Fuji X cameras does this from time to time, at what should be it's best apertures. I also remember a Nikon 24-120mm VR lens that had parts of the image looking like above.

So, is it me? is it the lens? is it some internal functioning thats causing the problem? I will be trying to get to the bottom of this, because in all other respects this is an excellent lens. When it's good, without this problem, it's actually very good.

Anybody got an ideas then please post them on Google+. 

(N.B. And I am expecting something more constructive than 'Its a crap Sony lens!' And if you do feel like you can't resist having a fanboy pop at Sony or this lens in particular, then be prepared to forego posting privileges.)

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