Sigma C 90 mm f/2.8 DG DN
7. Coma, astigmatism and bokeh
| Center, f/2.8 | Corner APS-C, f/2.8 | Corner FF, f/2.8 |
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| Center, f/4.0 | Corner APS-C, f/4.0 | Corner FF, f/4.0 |
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Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to 4.5 %. It's a very low value, not giving you any reasons to worry.
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Defocused circles of light look sensibly well. You can notice a slight trace of onion-ring bokeh and it stems from the fact that there is one aspherical element inside the optical stystem. On stopping down the aperture a rim appears on the edge of the circle but it is not especially intense. Mechanical vignetting is visible at the maximum relative aperture and on stopping down the lens by 1 EV; by f/5.6 it disappears completely.
| Center, f/2.8 | Corner APS-C, f/2.8 | Corner FF, f/2.8 |
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| Center, f/4.0 | Corner APS-C, f/4.0 | Corner FF, f/4.0 |
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Center, f/5.6 | Corner APS-C, f/5.6 | Corner FF, f/5.6 |
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