Sigma A 70 mm f/2.8 DG Macro
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 horizontal and vertical MTF50 function values, amounted to 4.6%. It is a value considered by us as low and the maximum relative aperture contributes the most to it. On stopping down the aperture to f/4.0 the astigmatism decreases to a value lower than 2%, becoming practically imperceptible.
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When it comes to the appearance of out-of-focus areas it would be difficult to have any reservations. The circles reveal an even spread of light, without any local extreme points. Even the rim on the edge of the frame, which intensity increases with the stopping down, is not especially bothersome. Still the influence of mechanical vignetting remains noticeable; it can be marginalized only by f/5.6.
| 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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