Nikon Nikkor Z 20 mm f/1.8 S review - Coma, astigmatism and bokeh

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Nikon Nikkor Z 20 mm f/1.8 S

17 July 2020

Maciej Latałło

7. Coma, astigmatism and bokeh

Both Nikkors 1.8/20, the new, belonging to the Z system and the older, Nikon F version reflex camera one, share the same weak coma correction. In the case of the older model, instead of the classic 'comma' shape we saw distinct 'wings'; in the case of the new one coma makes itself felt by overall magnification and lengthening of the point-like source of light. The problem is so significant that it can be noticed already in the corners of the smaller APS-C/DX sensor and in the corners of full frame it becomes really pronounced. What's more, you can notice influence of coma on both detectors even on stopping down the lens by 1 EV. It is definitely not a piece of good news, especially for those who would like to employ this lens in astrophotography.

Center, f/1.8	Corner APS-C, f/1.8	Corner FF, f/1.8

Center, f/2.5	Corner APS-C, f/2.5	Corner FF, f/2.5

Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounts to 12.9%, a noticeable value on the borderline between medium and high level. In this category the reflex camera model fared a bit better.

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When it comes to out-of-focus areas they look very nice for a wide angle lens. Light spread in the circles is even, without any traces of onion ring bokeh which should be expected because of three aspherical elements in the optical construction. Even mechanical vignetting is visible mainly at the maximum relative aperture and then it disappears completely on stopping down the lens by 1-2 EV. A round of applause!

Center, f/1.8	Corner APS-C, f/1.8	Corner FF, f/1.8

Center, f/2.5	Corner APS-C, f/2.5	Corner FF, f/2.5

Center, f/3.5	Corner APS-C, f/3.5	Corner FF, f/3.5