So why is it so bad? Well here is what it does at 16mm.
Now having written all that, it may come as a surprise that I'm probably going to keep and indeed use this lens. The reasons for this are mostly negative however. The explanation for this is that it is a VERY useful zoom range for what I do, there are (slight) improvements over the 18-55mm and 16mm lenses in terms of edge and corner sharpness, the profile means I'm not having to do lots of post-processing correction work, and finally there isn't really an alternative as yet. As I said mostly negative.
Above are some of the pictures I shot today on my NEX-7, which after correction look fine, (assuming you haven't seen the original). The last one shows the substantial amount of correction that takes place using the Adobe Raw lens profile. As you can see I composed the original image in the knowledge that removing the distortion and vignetting would "lose" part of it. You can also clearly see that to remove the vignetting the image is, in effect, being cropped on all sides. Is this acceptable? I leave that for you to decide. I know what I think.
So far from a ideal solution, but a solution of sorts for those looking for a standard type zoom for a NEX camera, though this turns out to be somewhat less than the focal range promised.
Now I won't pretend that this software adjusting of lens faults doesn't go on elsewhere. My Nikon 28-300mm uses it, the Panasonic 7-14mm is well-known for it and it extends to prime lenses I've used as well. However once you see what is applied to the Sony 16-50mm all the adjustments for the other lenses appear somewhat minimal.
So if you are considering this lens, then as can be seen, it can be made to give decent results. But if you aren't using the latest versions of Photoshop and Lightroom then I would suggest that you might struggle to get decent results if you shoot raw. If you are happy with the jpgs. then you will (mostly) be problem free, though some of these still have a lot of distortion and some vignetting. See - http://soundimageplus.blogspot.co.uk/2012/12/more-on-sony-16-50mm-coping-with.html
Under the circumstances there is no way that I can give this lens any kind of recommendation, other than to say under the right circumstances and with the right software, decent results are possible.
I'm sure that most of the problems come from the attempt to reduce the size of a lens like this. That doesn't personally bother me, and in reality I wonder just how many people it does bother. However there is a vociferous section of the photographic internet who clamour constantly for gear to be as small (and pocketable) as possible, and made to be relatively inexpensive. Hopefully this lens and its poor implementation will demonstrate to these people that if that's what you ask for, this is what you might get.
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