Sigma C 18-200 mm f/3.5-6.3 DC Macro OS HSM
5. Chromatic and spherical aberration
As you can notice in photos below the longitudinal chromatic aberration of the tested lens is practically imperceptible. Here the Sigma can be only praised.
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The lateral chromatic aberration in 18-200 mm class lenses is not as easy to correct, though. Despite that fact the producers, with several versions of the Sigma 18-200 mm model, managed to achieve a noticeable progress. The 18–200 mm f/3.5–6.3 DC OS lens had the maximum lateral chromatic aberration level of 0.14%, never descending lower than 0.08%. Its successor, the 18–200 mm f/3.5–6.3 II DC OS HSM, could get values as low as 0.02-0.05%, not exceeding a value of 0.12% anywhere.
The graph shown below proves that with the newest model the results are similar.
The highest aberration you see at the widest angle: no matter what aperture you employ it will keep a constant level of 0.12-0.13%. Although these values are still deemed medium, they are in fact very close to high. At the longer end of the focal range there are less problems though. In the middle of the range the aberration is slight and at 200 mm it reaches a medium level.
It’s obvious Sigma doesn’t’ repeat the mistakes of its rivals. You can remind here the result of almost 0.26%, reached by the Canon EF-S 18–200 mm f/3.5–5.6 IS at 100 mm focal length or the result of the Tamron and the Sony DT 18–200 mm f/3.5–6.3 – both those devices got to 0.17% at their maximum focal length.
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Spherical aberration
The lens didn’t have any ‘focus shift’ tendency. Defocused images of light points in front of and behind the focus don’t differ significantly. It all makes us say that the tested lens corrects the spherical aberration in the right way.
