Sigma A 14 mm f/1.8 DG HSM review - Chromatic and spherical aberration

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Sigma A 14 mm f/1.8 DG HSM

14 July 2017

Arkadiusz Olech

5. Chromatic and spherical aberration

Chromatic aberration

As many as seven low dispersion elements in the optical system of the tested Sigma suggest the producers took proper care of the longitudinal chromatic aberration correction. The photos presented below confirm it – you won’t notice any huge problems. A slight colouring of out-of-focus images remains noticeable, though, so that aberration is not corrected in a perfect way.

Sigma A 14 mm f/1.8 DG HSM - Chromatic and spherical aberration

When it comes to lateral chromatic aberration it was a huge challenge, joining an angle of view of significantly more than 100 degrees and f/1.8 aperture. We were very curious how the Sigma would perform.

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The graph above proves that the producers once again should be praised. The aberration increases slightly from about 0.04% at the maximum relative aperture to 0.06% on more significant stopping down. Both values allow you to call the level low. The Irix 2.4/15 fared similarly here but its task was easier because of less extreme parameters. The Samyang 2.8/14 was a bit weaker in this category - its maximum results got to 0.13%. Once again the Canon EF 14 mm f/2.8L USM II performed the worst as, near the maximum relative aperture its lateral aberration level was over 0.17%.

Canon 5D III, f/1.8	Canon 5D III, f/11.0

Spherical aberration

First photos of this chapter don’t show any ‘focus shift’ effect but it doesn’t mean the spherical aberration is corrected in a perfect way. The appearance of out-of-focus light circles, created in front of and behind the focus, proves its existence but not necessarily on a high level. The centre of the circle before the focus is noticeably darker than the centre of the circle after the focus – it means the spherical aberration wasn’t corrected perfectly well.