Sigma AF 80-400mm f/4.5-5.6 EX APO OS - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

Distortion is very well controlled with this lens with marginal pincushion distortion at 80mm increasing to slight pincushion distortion at 400mm. This is nothing that you need to worry about in the field.

80mm:

200mm:

300mm:

400mm:

Vignetting

Typical for most full frame lenses it produces very little vignetting on APS-C type DSLRs. In the 80-300mm range the issue is negligible. At 400mm vignetting is a little more pronounced at 0.6EV but in most scenes this will be rarely visible and stopping down a little helps resolve the issue completely.

MTF (resolution)

The lens exhibited a very decent resolution performance in the lab. At 80mm the quality is already very good at wide-open aperture increasing to excellent results at medium aperture settings. There's a gradual decrease in performance towards the long end of the zoom range but the performance penalty isn't overly pronounced. At 400mm the lens is still capable to deliver a good to very good resolution at f/5.6. While not formally tested the contrast performance seems somewhat lower and there was a slightly visible centering defect. Stopping down to f/8 provides an extra kick resolving both issues - see e.g. the exceptionally sharp sample image of the monkey below.

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)

CAs (color shadows at harsh contrast transitions) are very low in the 80-300mm range with a maximum of around 0.5 pixels on the average at the image borders. The situation deteriorates significantly at 400mm with CAs beyond the 1 pixel barrier which may be disturbing at times.




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