Sigma A 14-24 mm f/2.8 DG HSM
7. Coma, astigmatism and bokeh
| Center, 14 mm, f/2.8 | Corner APS-C, 14 mm, f/2.8 | Corner FF, 14 mm, f/2.8 |
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| Center, 19 mm, f/2.8 | Corner APS-C, 19 mm, f/2.8 | Corner FF, 19 mm, f/2.8 |
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| Center, 24 mm, f/2.8 | Corner APS-C, 24 mm, f/2.8 | Corner FF, 24 mm, f/2.8 |
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The astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to just 2.3%. It is a negligible level so the astigmatism correction also should be considered very good. It’s worth mentioning that aberration showed a slight downward trend as the focal length increased. At 14 mm it amounted to 3.3%, at 19 mm it was 2.6% and at 24 mm it got to 1.0%.
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Out-of-focus areas in ultra-wide-angle lenses are rarely a priority; often enough they also prove to be not exactly pleasing to the eye. Because of exaggerations, enforced by rectilinear mapping in the frame corners, the circles of light in that place are elongated and might look unpleasant as they tend to meet in the frame centre. It is not a flaw of this lens, rather its characteristic feature – without that oversharpness there would be no obtuse angles of view; alternatively the distortion level would have been much higher. You get nothing for nothing and you cannot cheat the laws of physics. The circles generated by the Sigma 14-24 mm don’t look that bad. Their middle seems to be quite smooth and the only feature that sticks out is a slightly accented rim.
| Center, 24 mm, f/2.8 | Corner APS-C, 24 mm, f/2.8 | Corner FF, 24 mm, f/2.8 |
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| Center, 24 mm, f/4.0 | Corner APS-C, 24 mm, f/4.0 | Corner FF, 24 mm, f/4.0 |
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Center, 24 mm, f/5.6 | Corner APS-C, 24 mm, f/5.6 | Corner FF, 24 mm, f/5.6 |
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