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Sigma A 35 mm f/1.4 DG DN – first impressions

27 April 2021
Maciej Latałło

3. Autofocus and some remarks concerning optical properties

The autofocus of the Sigma A 35 mm f/1.4 DG DN combined with the Sony A7R III is noiseless but not especially quick. Running through its distance range and confirming the right position takes about 0.8-1 second. We also had an impression that the autofocus was a bit slower when going toward shorter distances than when going toward infinity. This performance doesn't bowl us over, especially as you deal here with truly journalistic 1.4/35 parameters. Still you have to remember we handled a pre-production specimen; usually constructors work hard till the very end to improve the efficiency of autofocus so we hope the final version will fare better.

Sigma A 35 mm f/1.4 DG DN – first impressions - Autofocus and some remarks concerning optical properties

When it comes to vignetting, it is significant at the maximum relative aperture, reaching a tad over 3 EV. Still, an important piece of news is that on stopping down the aperture to f/2.0 you can notice a significant decrease of that aberration and its value becomes definitely lower than 2 EV. Of course precise measurements will be made during the full test of the final version of the lens.

CEO of Sigma, Kazuto Yamaki, during his pre-release presentation of the new lens emphasized the fact that its performance against bright light was optimized. Optics specialists paid special attention to light reflections from the optics and from parts of the body as well. The Sigma company employs a special team that do simulations of unwanted light artifacts; a drawing below shows a result of such a simulation for reflections from an inner construction of the lens.


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Sigma A 35 mm f/1.4 DG DN – first impressions - Autofocus and some remarks concerning optical properties

The aim of such simulations is to diagnose potential problems as early as possible and, so to speak, nip them in the bud. The construction of the lens is improved after analysing simulation results so the performance against bright light can be optimized. Of course we decided to check the results in practice even if we dealt with a pre-production instrument and we didn't conduct our ordinary procedures.

Photos below show clearly that the constructors didn't manage to elliminate all light reflection problems. If you stop down the lens more significantly you can catch colourful flares with ease, especially when the sun is situated inside the frame. As you move the sun a bit outside you get a whole net of radial yellow rays of light; after moving the frame even further from the source of bright light your photos might feature a greenish spot in the corner.

Here Sigma optics specialists performed weaker than their counterparts who constructed the Sony 1.4/35 GM – that lens performed very well against bright light and didn't show almost any reflections.

Sigma A 35 mm f/1.4 DG DN – first impressions - Autofocus and some remarks concerning optical properties

Sigma A 35 mm f/1.4 DG DN – first impressions - Autofocus and some remarks concerning optical properties

Sigma A 35 mm f/1.4 DG DN – first impressions - Autofocus and some remarks concerning optical properties

Sigma A 35 mm f/1.4 DG DN – first impressions - Autofocus and some remarks concerning optical properties