Viltrox AF 25 mm f/1.7 Air review - Coma, astigmatism and bokeh

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Viltrox AF 25 mm f/1.7 Air

2 October 2025

Maciej Latałło

7. Coma, astigmatism and bokeh

Coma and optical aberrations of higher degree that contribute to deformations of point-like sources of light aren't very bothersome here. Images of a diode put in the frame corner are just slightly enlarged, without any distinct deformations. Once again a very nice surprse!

X-T30, f/1.7, centre	X-T30, f/1.7, Corner

X-T30, f/2.5, centre	X-T30, f/2.5, Corner

In order to make the situation clear and comprehensive we decided to present also crops taken from photos of the sky taken from the upper right-hand corner of full frame. This time we show shots by f/1.7, f/2.5, and f/3.6. This kind of test proved to be more demanding and revealed more detail. Instead of a small pie you see clearly a divided influence of classic coma, that turns a star into a small comma, and wings, that are created by higher degree aberrations.

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Corner, f/1.7	Corner, f/2.5	Corner, f/3.6

Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to 11.7%. It's a value considered by us as medium so not providing any serious reasons to complain.

Out-of-focus circles of light look nice, with even light spread, without any distinct local extreme points. Even onion-ring bokeh stemming from the presence of aspherical elements, is not especially accented. A brighter rim makes itself felt a bit, as its intensity increases with stopping down. Mechanical vignetting is also visible, especially at the maximum relative aperture, where the size of the circle in the frame corner is significantly diminished compared to its size in the centre. Still, that vignetting disappears completely on stopping down the aperture by 2 EV and it is a good piece of news.