Sigma 18-200 mm f/3.5-6.3 DC OS
7. Coma and astigmatism
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The lens manages the coma correction the best at 200 mm – at that point the level of this aberration is very low. It increases gradually with the shortening of the focal length, reaching the highest level at 18 mm. Only there it can be described as high. The lens’s performance is very similar to the performance of its competitors in this category.
When it comes to the astigmatism its quantity, understood as the average difference between vertical and horizontal MTF50 values, amounted to less than 9% which is a medium result. We must describe it in more detail though, because in this category the lens shows us two faces. The better one peeks at us in the 18-50 mm range, explaining partially the excellent result for these focal lengths – the astigmatism is just less than 4% there. The situation gets a lot worse when we progress to the 100-200 mm range where we record the astigmatism level of almost 14%, so rather high.
