Sigma A 24 mm f/1.4 DG DN – first impressions and sample images

8 August 2022
Maciej Latałło

3. Autofocus and several words about optical properties

At the beginning of this chapter we have to emphasize the fact that here we describe properties of a pre-production specimen. A comprehensive assessment of the Sigma's A 1.4/24 optical performance will be possible when we get the final version of that lens and test it thorougly.

Of course it is possible to draw initial conclusions about the quality of optics by looking at sample shots, published at the end of this material. It is clear that image quality is good even at the maximum relative aperture but I have an impression that the 1.4/20 model fared a tad better.

The Sigma A 1.4/24 shows distinctly lower vignetting for a change and its vaue we estimate as about 3 EV. It's a lot but it's always good to check reference levels. The wider, heavier Sigma 1.4/24 designed for reflex cameras, with a bigger front element, had vignetting of −2.94 EV. Keeping a similar level of brightness loss in case of a smaller, lighter lens designed for mirrorless systems is a praiseworth achievement.

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In case of the top Art line Sigma optics specialists don't give up on distortion correction, passing that task to camera's software – our photos show it clearly. You can observe just slight barrel distortion of about -1.3%, a result very similar to -1.2% shown by the DSRL predecessor of this lens.

Sony A7R III, 24 mm, JPEG
Sigma A 24 mm f/1.4 DG DN – first impressions and sample images - Autofocus and several words 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, and their intensity is low.

Sigma A 24 mm f/1.4 DG DN – first impressions and sample images - Autofocus and several words about optical properties

Joined with the Sony A7R III the autofocus of the Sigma A 1.4/24 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 the new Sigma will perform a bit better in this category.