Pictures taken with Sigma 17-70 mm f/2.8-4 DC Macro OS HSM – Contemporary and Nikon D5100

The Sigma 17-70 mm f/2.8-4 DC Macro OS HSM Contemporary is designed as an upgrade to the 18-55mm kit lenses supplied with most APC-C DSLR (Nikon, Canon, Sony, Pentax - non full-frame versions), and offers an interesting middle ground between fast zooms of the 17-50mm F2.8 type, and extended-range zooms in the 16-85mm class.
The new Sigma the 17-70mm (not to be confused with old version 17-70mm) can be an excellent choice if you've grown out of a kit zoom and want something a bit better. It offers generally better optics, a broader zoom range, and of course that faster aperture (f/4). It is compact (8cm in length), so doesn't take up too much extra space in your camera bag. It's not as light as a kit zoom, but not excessively heavy either (462g).
The lens's focusing and image stabilization systems work well too. Auto-focus is pretty fast, and near-silent when shooting stills; the OS system is silent in operation, and works generally very well.
The 'Macro' mean the Sigma 17-70mm Contemporary can focus from 22cm/11in (0.37x magnification), but you must be careful not to cast shadow on your subject or blocking out your own light.
Build quality is also excellent, with the brass lens mount, sober all-black design and lens hood it is included.
The Sigma 17-70 mm f/2.8-4 DC Macro OS HSM Contemporary (C) main weakness is its image quality at wide-angle; here it suffers from somewhat soft edges which don't sharpen up on stopping down. Vignetting at wide-open apertures and barrel distortion at 17mm are present, but both can be easily correctable in post-production.
I use FastStone Photo Resizer (2000px on long side, quality 95) and Romanian version can be found at my blog: http://www.fotostefan.ro/test-cu-sigma-17-70mm-f2-8-4-dc-macro-os-hsm-contemporary-pentru-nikon/