Sirui Aurora 85 mm f/1.4 review

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Sirui Aurora 85 mm f/1.4

5 October 2026

Maciej Latałło

4. Real relative aperture

Having learned from our experience with the Aurora 1.4/35 test, which showed clear problems with the aperture stopping down, we decided to check how the situation looks with the 85 mm model. Right from the start, however, we knew that the Aurora 1.4/85 performed better in this respect, as its resolution results at individual aperture settings did not look suspicious. The only exception was f/16, where the results were clearly too high.

The photographs below show that the situation is indeed better because, unlike the 1.4/35 model, the aperture here is circular and does not show any noticeable asymmetry.

Sirui Aurora 85 mm f/1.4 - Real relative aperture

Once again, assuming that the f/2.0 aperture is represented correctly, we can treat it as the baseline and check what happens at the more stopped-down settings. The next two steps are rendered correctly, as our measurements showed values of f/2.806 and f/4.035. The aperture therefore operates correctly in the f/2.0–f/4.0 range. It then stops down somewhat more strongly, with the next value being f/5.867, but further on the situation reverses, and the subsequent steps are noticeably smaller than the square root of two. Continuing, we therefore obtain actual aperture values of f/8.119, f/10.889, and f/12.359.

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This confirms what we observed in the resolution measurements. Between the declared apertures of f/11 and f/16, instead of a 1.414× step, there is only a 1.135× change. As a result, the smallest available relative aperture of the Aurora 1.4/85 is not f/16, but a value closer to f/12.

Once again, this raises the question of why one would boast about an aperture with a record-breaking 15 blades, only to stumble when it comes to stopping it down...

In the case of a lens with a longer focal length, it is somewhat easier to photograph and determine the size of its entrance pupil. Once again, assuming that the f/2.0 relative aperture is correct, we can attempt to determine the actual light-gathering capability of the tested model. It appears to be worse than the declared f/1.4 value (or, more precisely, f/1.414), as our measurement yielded f/1.520. Even taking measurement errors and our assumptions into account, it therefore seems that the actual maximum aperture of the SIRUI Aurora 1.4/85 is closer to f/1.5 than f/1.4.

Our observation may be supported by the size of the front element. Although, as we noted in the previous chapter, it is not identical to the entrance pupil, the front element has a diameter of 58 mm. Meanwhile, dividing 85 mm by f/1.4 gives a theoretical entrance pupil diameter of 60.7 mm, which is noticeably larger than the front element.