Sigma A 20 mm f/1.4 DG DN – first impressions and sample images

8 August 2022
Maciej Latałło

3. Autofocus and some remarks about optical properties

A comprehensive assessment of the Sigma lens's optical performance will be possible when we get the final specimen of that lens and test it thorougly. Still even now, after taking photos with the pre-production model, we can draw some conclusions.

Sample shots, presented at the end of this material, show clearly that sharpness shouldn't be an issue here. Even by f/1.4 you are able to get images of very good quality.

Vignetting is quite another story as it is able to reach near 3.5 EV. It's a lot but not a big surprise; even the reflex camera version of this lens exceeded 3 EV and with the new lens the standards are raised even higher. Why? Firstly, there are more problems with telecentricity. Secondly, the new version allows you to attach traditional 82 mm filters and that limits the dimensions and convexity of the optical front element system. Mind you it's difficult to compare this lens directly to any other instrument because none of its rivals offer similar parameters.

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Contrary to the C line lenses, the Art series tries to control distortion with the help of the optics and the result of the new 20 mm model near -2.5% is the proof. It is a bit weaker than in case of its reflex camera predecessor but the difference is not that significant. With such a wide angle of view deformations of such a degree can be deemed acceptable.

Sony A7R III, 20 mm, JPEG
Sigma A 20 mm f/1.4 DG DN – first impressions and sample images - Autofocus and some remarks about optical properties

When it comes to the performance against bright light, the task of Sigma optics specialists was very difficult indeed - you deal here not only with a complex optical construction, an ultra-wide angle of view, but also with a huge front element. The bar was raised very high but Sigma managed to jump it. The overall contrast of images is really good, light artifacts are few and far between, appearing mainly when you put the sum really close to the frame centre.

Sigma A 20 mm f/1.4 DG DN – first impressions and sample images - Autofocus and some remarks about optical properties

Joined with the Sony A7R III the autofocus of the Sigma A 1.4/20 is completely noiseless but its speed hardly bowls you over. There is too much 'focus play' so a distinct oscillation near the proper position and it slows the whole process down noticeably. Still in the majority of cases the lens's focus speed is below 0.8-0.9 of a second.

It's worth mentioning here that the autofocus module is often a feature that can be significantly improved in the final version of a lens so we hope the final specimen of this lens will perform a bit better in this category.