Carl Zeiss Otus 55 mm f/1.4 ZE/ZF.2 review - Coma, astigmatism and bokeh

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Carl Zeiss Otus 55 mm f/1.4 ZE/ZF.2

18 November 2013

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The coma might be a huge problem for the 1.4/50 class lenses – you can find out how huge by checking the appropriate chapter of our test of the Voigtlander 1.4/58. The Zeiss Otus fares much better here. On the small sensor the coma is almost not bothersome at all but it can be noticed in the corners of full frame; still even there its level is just medium. The fact that the coma doesn’t change almost at all when you stop down the aperture from f/1.4 to f/2.0 is interesting, though. Such an effect is partially responsible for the fact that both these apertures are a bit below the decency level when it comes to the resolution on the edge of the frame.

Carl Zeiss Otus 55 mm f/1.4 ZE/ZF.2 - 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.