Sigma AF 50-150mm f/2.8 EX DC HSM (Nikon mount) - Review / Test Report - Analysis
Lens Reviews - Nikon / Nikkor (APS-C)

Distortion

The Sigma produces slight barrel distortion at 50mm (~0.8%) changing to slight pincushion distortion at 100mm (~0.9%) and moderate pincushion distortion (~1.4%) at 135mm.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
50mm 100mm 150mm

The chart above has a real-world size of about 120x80cm.

Vignetting

As mentioned in the introduction the Sigma is a dedicated APS-C lens with correspondingly smaller glass elements. This results in a comparatively higher degree of vignetting - less so at 50mm and 100mm but at 150mm the problem is fairly pronounced (1EV @ f/2.8). In critical situations you should stop down to f/4 here.

MTF (resolution)

The Sigma was able to produce very impressive resolution figures in the MTF lab. This is especially true for the 50mm and 100mm setting where the center to border characteristic is generally excellent from f/2.8 down to f/8 (apart from a few very good+ border and extreme corner portions). At 150mm there's a drop in quality specifically at f/2.8 - the center and border is still very good but the extreme border quality drops down to only fair quality here. However, the corners do pretty much catch up by f/4. The peak performance is reached between f/5.6-f/8 with an excellent center and very good borders/corners.

It is worth to mention that this doesn't seem to be the complete story. At 150mm I wasn't really able to get any good field images from this lens at very close focus distances (<1.5m). The contrast level is very poor here (SAMPLE). To be fair this is normal up to some degree for all non-macro lenses but in my opinion Sigma should have chosen a more conservative minimum focus distance.

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 Chromatic aberrations (color shadows at harsh contrast transitions) are very well controlled for a zoom lens. At 50mm and 100mm it's pretty much a non-issue. This is also true at 150mm @ f/2.8-4 but beyond CAs are increasing to (still) moderate levels.




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