Viltrox AF 15 mm f/1.7 Air
7. Coma, astigmatism and bokeh
| X-T30, f/1.7, centre | X-T30, f/1.7, corner |
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| X-T30, f/2.5, centre | X-T30, f/2.5, corner |
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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. Usually stars are a more demanding test than the diode itself and here it's clear that, apart from a slight blow-up of image you see places where small rays of light spread out. Coma is not corrected in a perfect way but, on the other hand, the lens's performance shouldn't be seriously criticized.
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| corner, f/1.7 | corner, f/2.5 | corner, f/3.6 |
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Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to 8.1%. It's a value considered by us as low. At the same time you should add that this aberration remains visible only by f/1.7 and f/2.0; by f/2.8 it becomes practically zero.
Defocused circles of light look sensibly well for a wide angle lens. You can notice very delicate onion ring bokeh and a brighter rim which intensity increases with stopping down. Still these are not features that should surprise you. Mechanical vignetting is also not especially bothersome, disappearing completely after stopping down the aperture by 2 EV.
| X-T30, f/1.7, centre | X-T30, f/1.7, corner |
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| X-T30, f/2.5, centre | X-T30, f/2.5, corner |
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| X-T30, f/3.6, centre | X-T30, f/3.6, corner |
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