Samyang AF 24-60 mm f/2.8 FE
7. Coma, astigmatism and bokeh
In the middle of the focal range, coma is already a tad more bothersome because the dimensions of a diode increase and this effect remains visible in the corners of both types of detectors. Problems become only more serious after passing to 60 mm where images of a diode become even bigger and they get 'wings' in the corner of full frame – their presence means higher-degree aberration aren't corrected well.
| 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, 40 mm, f/2.8 | Corner APS-C, 40 mm, f/2.8 | Corner FF, 40 mm, f/2.8 |
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| Center, 60 mm, f/2.8 | Corner APS-C, 60 mm, f/2.8 | Corner FF, 60 mm, f/2.8 |
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To make our test more interesting, we also decided to show the image of a bright star put in the frame corner. These photos confirm the conclusions from the paragraph above. Additionally, the 'wings', described earlier, and appearing at a combination of the maximum focal length and maximum relative aperture are much more distinct here.
| Corner FF, 24 mm, f/2.8 | Corner FF, 24 mm, f/4.0 | Corner FF, 24 mm, f/5.6 |
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| Corner FF, 60 mm, f/2.8 | Corner FF, 60 mm, f/4.0 | Corner FF, 60 mm, f/5.6 |
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Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to 12.7%. It is a value we consider to be average. We didn't spot any significant differences between particular focal lengths. Getting nice out-of-focus areas in a zoom lens with as many as three aspherical elements is not that simple. Small wonder the Samyang didn't manage to handle this task. Defocused circles of light show a lot of heterogeneities and onion-ring bokeh can also be felt. The rivals prove that the performance in this category could have been a tad better.
There are no reservations concerning mechanical vignetting for a change. Already by f/4.0 it is slight and on stopping down to f/5.6 it disappears completely.
| Center, 60 mm, f/2.8 | Corner APS-C, 60 mm, f/2.8 | Corner FF, 60 mm, f/2.8 |
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| Center, 60 mm, f/4.0 | Corner APS-C, 60 mm, f/4.0 | Corner FF, 60 mm, f/4.0 |
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Center, 60 mm, f/5.6 | Corner APS-C, 60 mm, f/5.6 | Corner FF, 60 mm, f/5.6 |
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