Canon EF 200 mm f/2.0L IS USM
7. Coma, astigmatism and bokeh
The astigmatism is quite another matter - it is clearly more pronounced than the coma. Its level is perhaps not exactly high because the average distance between vertical and horizontal MTF50 function values amounts to 7.3% but it is not as negligible as in the case of the coma.
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After attaching the converter the astigmatism doesn’t change its level- officially it was 7.8% so, within the margin of error, the same as for the lens itself.
Let’s glance once again at a defocused image of a diode put in the frame centre, in the corner of the APS-C sensor and in the full frame corner as well.
It can be noticed that the light in the circles is very evenly spread. What’s more, already by f/4.0 the light circles are almost exactly the same no matter where the diode was positioned. You can expect the blurred areas will be smooth and pleasant to the eye.
