For luminous intensity:
The 1: 2.8 at 17mm like hide something, especially since they at 70mm to 1: 4.0 shrinks. However, it has saved me for landscapes at dusk already sometimes
Optical power:
To anticipate: maximum aperture is not your thing, there is a bit blurred in the corners, from 1: 5.6 to be on the safe side.
In CA I did not explicitly investigated, vignetting I have not found.
Zoom range:
17-70 may seem a bit thin, but it is not. Even the 1mm less down compared to the 18-xxx lenses brings a clear 'More' on the image.
Autofocus:
Works quickly, quietly and reliably. Front or back focus seems to be an issue in the Niko models.
Processing:
Wertig, with a pleasant feel. Nothing wobbles or rattles, even after 3 months. What really bothers:
The focus ring rotates with and fiddly switches M / AF, a manual focussing in AF operation is not possible, other manufacturers have solved the better.
The adjustment path of the focus ring is a bit short.
Other:
The lens has a macro function, ie from 40 mm the magnification greater than 1: 4 is, thus, the criterion of a macro is met. One should not however be compared with the performance of a fixed focal length you get quite usable shots.
Price:
For what it may, it is almost a bargain. No silver bullet but very solid in use and appearance.
Summary:
Very satisfied, actually a 9 out of 10. For 5 stars it is in absolute not good enough, see S / AF switch, in relation to the price but my absolute recommendation.
Addendum of 11/04/2012
Had this the lens at several concerts in which I had the opportunity, at close to Fotgrafieren. On this occasion, the OS takes full effect. Does the OS for small focal lengths with "normal" light rather a subordinate role, so it shows its efficiency especially in these Lichverhältnissen. Of course you have to fire at a plethora of musicians Series until you get an image with no or little motion blur, but the image is not blurred. When f = 50mm remain nevertheless still 1: 3.5 left - so you can work well.
By the way, the AF works! Extremely reliable even in dim light. The longer I use the lens, the more I like them.
In this context I would like to refer to the review of Photozone.de:
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