Sony FE 85 mm f/1.8 review - Chromatic and spherical aberration

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Sony FE 85 mm f/1.8

15 March 2019

Arkadiusz Olech

5. Chromatic and spherical aberration

Chromatic aberration

The Sony lens, contrary to its older rivals such as e.g. the Canon EF 85 mm f/1.8 USM or the Nikkor AF-S 85 mm f/1.8G, features low dispersion glass elements so we expected it woudln't have problems with longitudinal chromatic aberration. We were right. Images below show clearly that the colouring of out-of-focus areas is slight; overall that aberration is far less noticeable than in the case of the Canon and the Nikkor.

Sony FE 85 mm f/1.8 - Chromatic and spherical aberration

Now let's check the correction of lateral chromatic aberration – its correlation with the aperture and the size of the detector presents a graph below.

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The situation is interesting: the aberration won't bother you only near the maximum relative aperture but it will increase with the stopping down of the aperture very quickly, being on the borderline between low and medium levels by f/22. Here the Sony fares noticeably weaker than the Canon 1.8/85, which got results of about 0.01-0.03%, and the Nikkor which even at its worst, so by the maximum relative aperture, didn't exceed 0.08%.

A7R II, RAW, f/1.8	A7R II, RAW, f/16.0

Spherical aberration

First photos of this chapter don't show any 'focus shift' symptoms so spherical aberration level can't be high or very high. Defocused circles of light are the proof that it is not corrected in a perfect way either. A circle behind the focal point has a slightly accented rim and the one you get before the focus is devoid of that feature. It is a classic example of spherical aberration and it shows that the optics doesn't deal with it as it should. The observed effect still remains slight and it doesn't change our positive assessment of the lens in this category.