Sirui Aurora 35 mm f/1.4 review

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Sirui Aurora 35 mm f/1.4

7 August 2026

Maciej Latałło

4. Real relative aperture

During the analysis of resolution results we noticed suspiciously high values for apertures that are stopped down more significantly. For example by f/16, a place where practically all lenses work in their difraction limit, their results are roughly the same, keeping a level of 40-42 lpmm. In case of the Sirui it was 49 lpmm. We assumed at once that the lens might have problems with the proper closing down of the aperture.

One glance at the photo below and you know that indeed the situation is not especially good here.

Sirui Aurora 35 mm f/1.4 - Real relative aperture

We wonder: why boast of a record number of aperture blades, 13 not less, and then fail to close them down properly, making the aperture round as it should be? Every example presented above proves that the relative aperture is rather elliptic.

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As if it wasn't enough, the real values of the relative aperture are nowhere near the declared ones. Because of some design features, we had some troubles with measuring the maximum relative aperture, so we decided to apply a simplified approach. We assumed that the f/2.0 aperture indeed reflected the declared value and we checked how it changed with further stopping down. In a perfect case every next aperture should be by a root square of two (so 1.414) smaller than the previous one. In the case of the Sirui all other values, apart from one, amounted to less than 1.4, 1.37 on average.

To be precise, all following apertures after f/2.0 amounted to: 2.778, 3.749, 5.218, 7.536, 10.330 and 13.450. Small wonder that resolution results on more significant stopping down are overstated.