Sigma C 23 mm f/1.4 DC DN – first impressions and sample images
3. Several words about optical properties and autofocus
Image quality
Although we dealt with a pre-production model, our sample shots show clearly that the lens doesn't have any problems whatsoever with achieving good image quality already at the maximum relative aperture. It seems the Sigma C 23 mm f/1.4 DC DN will continue a good streak of well-done Contemporary f/1.4 lenses.Chromatic aberration
The photo below shows very clearly that the Sigma C 23 mm f/1.4 DC DN, despite its supreme aperture fastness, doesn't have any noticeable problems with longitudinal chromatic aberration. Mind you, the task is not easy so the lens should be praised for this performance.A6400, f/1.4 |
Distortion
In the Contemporary series distortion correction is left to software of a camera to deal with. It gives the constructors more room when it comes to fighting off other aberrations, not so easy to correct with software.In case of the new Sigma you see barrel distortion of -2.7%. It is a noticeable level but, at the same time, it doesn't give you any serious reasons to complain.
Sony A6400, 23 mm, JPEG | |||
Vignetting
A combination of a wide angle of view, and the f/1.4 aperture is always a challenge when it comes to vignetting correction. It seems here problems are unavoidable because, when it comes to the maximum relative aperture, you deal with brightness loss in frame corners reaching about 60% (-2.6 EV), and it decreases to arround 38-39% (-1.4 EV), on stopping down the aperture to f/2.0.
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These are high levels but, after all, it's a Contemporary device. The producers emphasize the fact that in these lenses vignetting and distortion correction aren't on a list of their priorities as they are easy to correct with software.
A6400, APS-C, f/1.4 | A6400, APS-C, f/2.0 |
Flares
Ensuring good performance against bright light with such parameters of the lens and its optical comlexity, was not an easy task. Despite that fact Sigma dealt sensibly well with this problem. Of course we handled a pre-production model but it seems that its anti-reflection coatings should remain as they are – they are efficient enough.Autofocus
The autofokus of the Sigma C 23 mm f/1.4 DC DN attached to the Sony A 6400 is noseless and moderately quick. Running through its whole distance range and confirming the focus takes about 0.7-0.8 of a second. If you switch the autofocus into the AF-C mode the mechanism is able to speed up and then focusing lasts about 0.5 of a second.Mind you, while shooting our samples outdoors we noticed a very strange performance. Many times the mechanism chose a definitely wrong position – so wrong that you could notice the image was out of focus even by looking into the viewfinder. You had to press the shutter button again and only then, more often than not, the focus was set properly.
In this case we once again emphasize the fact that we deal with a pre-production model of the lens. Most often new software improves the focusing mechanism exactly and we hope the final model won't experience any problems in this category.