Sigma 17-70mm F2.8-4 Contemporary
Sharpness
Sharpness is undoubtedly one of the key components of image quality. In order to gauge the Sigma 17-70mm's sharpness, we compare it to the Pentax 18-135mm, a super-zoom lens with "consumer" rather than "prosumer" image quality.
Center Sharpness - Wide
Sigma @ 17mm, Pentax @ 18mm | |
| F2.8/3.5 |   |
| F4 |   |
| F5.6 |   |
| F8 |   |
| F11 |   |
| F16 |   |
Center Sharpness - Normal
Sigma @ 50mm, Pentax @ 50mm | |
| F3.5/4.5 |   |
| F4 |
|
| F5.6 |   |
| F8 |   |
| F11 |   |
| F16 |   |
Center Sharpness - Tele
Sigma @ 70mm, Pentax @ 70mm | |
| F4/4.5 |   |
| F5.6 |   |
| F8 |   |
| F11 |   |
| F16 |   |
Corner Sharpness - Wide
Sigma @ 17mm, Pentax @ 18mm | |
| F2.8/3.5 |   |
| F4 |   |
| F5.6 |   |
| F8 |   |
| F11 |   |
| F16 |   |
Corner Sharpness - Tele
Sigma @ 70mm, Pentax @ 70mm | |
| F4/4.5 |   |
| F5.6 |   |
| F8 |   |
| F11 |   |
| F16 |   |
Sharpness Verdict
The test chart photos show that generally speaking, the Sigma 17-70mm is at its best when stopped down by about 1 to 3 stops. Its sharpness wide-open is good, except at 70mm, where stopping down to F5.6 carries a significant benefit.
The center sharpness of the 17-70mm is only slightly better than that of the 18-135mm. In the corners at the wide end, however, it's an entirely different story; the Sigma is noticeably sharper than the Pentax superzoom. When zoomed in to 70mm, the corner sharpness of the two lenses is about the same.
Test charts aside, in real-world photos you will find the 17-70mm to be exceptionally sharp (for a zoom) just about everywhere, with the exception of the corners and edges at the long end. Click on the photo above to download an unedited full-size photo taken at 55mm.
This latest version of the Sigma 17-70mm is slightly sharper than both of its predecessors, which means that you can expect it to outperform the Pentax-DA 17-70mm F4 as well.
