Yongnuo YN 35 mm f/2.0
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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Astigmatism might be another reason. Its level is not as high as that of the coma but it is rather bothersome. In fact it could also be turned into a textbook example; below you can find a graph with measurements we got using our biggest testing chart. MTFs for vertical border and horizontal border are marked separately.
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At the maximum relative aperture the difference between horizontal and vertical MTF50 function values is over 18% and it decreases to 10.7% by f/2.8. The astigmatism becomes low (6%) by f/4.0 but, as it is showed on the graph, it disappears only by f/5.6-8.0.
We don’t have any reservations concerning the appearance of defocused images. The light spread is more or less even and the effects connected to the mechanical vignetting disappear completely already by f/4.0.
| 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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