Panasonic Lumix S 18 mm f/1.8
5. Chromatic and spherical aberration
Chromatic aberration
As we've seen in chapter 3, the optical construction of the tested lens features a lot of special elements; small wonder that, despite parameters that are not easy to correct you don't observe any meaningful problems with curbing longitudinal chromatic aberration.Colouring of out-of-focus images is very slight, visible only and solely near the maximum relative aperture. We think this effect is so slight that it would be very difficult to notice in real life photos.
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At the maximum relative aperture this aberration level is near 0.09%, on the borderline between low and medium values. Stopping down of the aperture provides a very clear effect, with results decreasing swiftly to near 0.06%. Overall we don't have any reservations here but still it's worth adding that both Sony models fared in this category noticeably better. The 1.8/20G model had an especially good result, never exceeding 0.03%. The Sigma A 20 mm f/1.4 DG DN, a lens from a bit different segment but also available as an L-mount version, performed equally well.
| S1R II, 18 mm, RAW, f/1.8 | S1R II, 18 mm, RAW, f/11.0 |
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Spherical aberration
In first photos from this chapter it would be difficult to notice any focus shift effect and it means that spherical aberration cannot be high. Still, defocused circles of light we got before and behind the focus, prove that its correction is hardly perfect. You get a classic symptom of this aberration, with soft edges of the circle in one case, and a bright rim in the second one.
| S1R II, 18 mm, f/1.8, before | S1R II, 18 mm, f/1.8, after |
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