Sigma A 85 mm f/1.4 DG HSM
5. Chromatic and spherical aberration
Longitudinal chromatic aberration is not corrected in a perfect way – its slight influence can be noticed near the maximum relative aperture. Still the observed level of the aberration is nothing to carp about and the tested lens shouldn’t be criticized because of it, especially that by f/2.0 the problems practically cease to exist. It also should be noticed that its result is better than the result of its predecessor.
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Now let’s check how the Sigma A 1.4/85 deals with the lateral chromatic aberration – the appropriate graph is shown below.
The results are quite sensational. No matter what detector is used, the aberration level oscillates near 0.01- 0.02%. It means you’ll have problems with noticing the chromatic aberration in real life photos even if you examine blown-up crops in great detail. Similarly excellent values in this category had both Zeisses, the Otus and the Milvus; the tested lens fares a bit better than its direct predecessor, the Canon EF 85 mm f/1.2L II USM and the Nikkor AF-S 85 mm f/1.4G.
|Canon 5D III, f/1.4||Canon 5D III, f/5.6|
First photos of this chapter don’t feature any noticeable “focus shift”. Still if you look closely you can see a slight shift of the depth of field toward the greater distances when you pass from f/1.4 to f/2.0. Looking at the circles of light you can also perceive vestigial spherical aberration. Overall the image looks very nice but the circle in front of the focus has soft edges and the circle behind the focus – a delicate outline.
Both these effects mean the spherical aberration is not corrected in a perfect way but its influence remains slight so it would be difficult to consider it a serious flaw. That verdict is additionally confirmed by high resolution values across the frame by f/1.4 and lack of characteristic mist in photos.
|Canon 5D III, f/1.4, in front of||Canon 5D III, f/1.4, behind|