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Sigma AF 17-70mm f/2.8-4 DC HSM OS | C (Nikon) - Review / Test Report - Analysis |
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Lens Reviews -
Nikon / Nikkor (APS-C)
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Page 2 of 3
Distortion
The distortion figures of the Sigma are fairly typical for such a standard zoom lens. At 17mm the lens shows quite pronounced barrel distortion (~3.1 %) and moderate pincushion distortion at longer focal lengths. The two opposing distortion types even out at around 24mm where images are basically distortion-free.
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Move the mouse cursor over the focal length text marks below to observe the respective distortion
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| 17mm |
24mm |
35mm |
50mm |
70mm |
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The chart above has a real-world size of about 120x80cm.
Vignetting
Because of its quite large aperture at the shortest focal length, it's hardly surprising that the lens shows the highest amount of light fall-off at this setting, reaching up to 1.2 EV. As usual, stopping down helps to significantly reduce the issue.
At longer focal lengths the issue is less pronounced at large aperture settings.
MTF (resolution)
The lens delivers very good to excellent resolution in the image center at all tested focal lengths.
The borders and corners are a bit soft at the shortest focal length and large apertures, but improve to very good figures by stopping down. At all other focal lengths the lens delivers good to very good resolution across the frame.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations
Chromatic Aberrations (CAs)
Lateral CAs (color shadows at harsh contrast transitions) are very well controlled including the critical 17mm setting. The CAs reach values of just below 1.5 pixels here. This may be noticeable at 100% image magnification on your screen but it's not really relevant anymore for prints.
In addition, please note that CAs can easily be corrected in software or by the camera itself (most modern Nikon DSLRs remove CAs themselves if you shoot JPGs).
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