Carl Zeiss Otus 55 mm f/1.4 ZE/ZF.2
7. Coma, astigmatism and bokeh
The Zeiss Otus 1.4/55 is also not completely astigmatism-free. The average difference between horizontal and vertical MTF50 function values amounted to 11.5% which we consider to be a medium result. Still it should be mentioned that the astigmatism disappears completely near f/4.0. The graph below shows in more detail how the tested lens performs in this category, with MTF50 values for vertical and horizontal borders marked separately. You can notice that from f/4.0 the results, within the margin of error, are practically identical.
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The appearance of the defocused light points deserves our praise. The light spread is very even and smooth so you can expect a very pleasant blurred background. The only reservation concerns distinct truncation of the circles in the frame corners, visible even on stopping down the aperture to f/2.8 but it is a result of vignetting, which we are going to describe in full in the next chapter.