Sigma S 200 mm f/2 DG OS
7. Coma, astigmatism and bokeh
| Center, f/2.0 | Corner APS-C, f/2.0 | Corner FF, f/2.0 |
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| Center, f/2.8 | Corner APS-C, f/2.8 | Corner FF, f/2.8 |
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In order to present a comprehensive image in this category we decided to add crops taken from photos of sky taken from the upper right-hand corner of full frame. This time we show photos taken by f/2.0, f/2.8, and f/4.0. In this case coma is very similar to the appearance we registered during our diode test because the main effect consists of slight enlargement and very slight deformation of point-like images of stars. All this decreases on stopping down.
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| Corner FF, f/2.0 | Corner FF, f/2.8 | Corner FF, f/4.0 |
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Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to 5.8%. It is a value positioned on the borderline of very low and low levels so not providing any reason to complain.
Defocused circles of light, generated by the Sigma, look very well. There are no local extreme points visible and the rim that appears on stopping down the aperture, is not especially intensive. It would be difficult to have any reservations concerning mechanical vignetting because it disappears almost completely on stopping down the aperture by 2 EV.
| Center, f/2.0 | Corner APS-C, f/2.0 | Corner FF, f/2.0 |
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| 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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