Sigma 105 mm f/2.8 EX DG Macro
7. Coma and astigmatism
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The high image quality at the edge of the field stops being a mystery when we look closely at such off-axis aberrations as coma and astigmatism. The first is corrected in a practically perfect manner as it is shown in the picture below.
With the astigmatism we see the same story. Near maximum relative aperture the average difference between vertical and horizontal MTF50 function values amounted to just 5.7%. It’s worth adding here that so far we’ve seen just few lenses which managed to go below 5% in this category.
