Viltrox AF 85 mm f/2 EVO
5. Chromatic and spherical aberration
Chromatic aberration
In case of the 85 mm focal length we consider a lens to be fast when its aperture ranges from f/1.2 to f/1.4. The f/2.0 relative aperture is not so difficult to correct when it comes to longitudinal chromatic aberration so the Viltrox had it relatively easy here. Apart from that its optical construction features two low dispersion glass elements. We are not that surprised that the tested lens didn't show any significant problems with the correction of this aberration.Photos below show that you can notice just a very slight colouring of images in out-of-focus areas positioned further away only at the maximum relative aperture. Mind you even in that place it remains so slight that it won't be bothersome in real life photos for sure.
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Now let's check how the Viltrox AF 85 mm f/2 EVO deals with correction of lateral chromatic aberration – the performance depending on used detectors and aperture values presents a graph below.
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You can see at once that the results are simply splendid. The aberration depends weakly on the aperture value and the size of the detector; in fact all results are within the 0.02-0.03% range so always very low. A round of applause!
| A7R IIIa, RAW, f/2.0 | A7R IIIa, RAW, f/11.0 |
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Spherical aberration
First photos of this chapter feature a slight focus shift effect – depth of field on stopping down starts to encompass more and more areas positioned behind the focus. Still this effect is hardly pronounced and, as a result, the proper aim remains in the sharpness plane.Lack of any more serious problems connected with spherical aberration confirms the appearance of out-of-focus circles of light we got before and behind the focus. They are very similar to each other. If you add to them a very high resolution the Viltrox offers up from the maximum relative aperture you can say that spherical aberration is kept well in check. A small amount of this aberration might have been left deliberately in order to ensure nicer out-of-focus areas in images.
| A7R V, f/2.0, before | A7R V, f/2.0, after |
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