Lets cut to the chase - you are reading this because you may be considering a wide-angle lens for your Z mirrorless camera and want to know if this lens is as good as Nikon says it is. Yes, the Nikon 20mm f/1.8 is as Nikon states a superior wide-angle lens - flat out.
This lens features an impeccable build quality with excellent weather seals with a fluorine coating to help repel dust and water and is about the same size as the 24-70 Kit lens.
Focusing is extremely fast and accurate with this lens, faster than my 24mm f/1.4 f mount lens on my trusty Nikon D850., the 20mm F/1.8 S lens is super fast and quiet. But keep in mind the Nikon Z lenses are not a direct coupling to the lens elements - it is focused by wire which reduces that tactile feel of the older lens focusing system. Neither the less, the automatic focusing system works and I found myself never needing to switch to manual focusing. Be aware also, that once focus is achieved and you turn off your camera then turn it back on - your focus point will not be set to where you expect it. I am not sure if other mirrorless cameras share this issue but Nikon DSLRs did not.
Focusing distance is very reasonable with a 1:5 ration at the closest focus point - meaning you can get close-ups of plants/flowers if you so desire, No it is not a macro lens but does allow a reasonable close focusing distance of 0.66 ft. (0.2m) from the focal plane.
Sharpness: Center sharpness is extremely sharp - you will not be disappointed. No comparison between the older 20mm F mount lens and this new 20mm S lens, The 20mm f/1.8 S lens simply blows the older lens away in sharpness.
Corner Sharpness is once again held superior in the Nikon 20MM f/1.8 S lens, far superior over the older legacy lenses. You really don't know how un-sharp your older F mount lenses are until you compare them to the newer technology of the S lenses. In all comparisons, the S lenses are superior across the board.
if you are into night time shooting - street scenes or the night sky, you will be pleasantly surprised to know this lens excels at both. Pinpoint stars corner to corner, with well-controlled light flares and ghosting from street lamps. Chromic Abbreavtion is well controlled in the Nikon 20mm S lens but there is some when shooting wide open but nothing too serious, the new S lens holds its own more than the older legacy lenses.
Barrel Distortion: The New Nikon S 20mm Lens does have slight barrel distortion at around 1.9%, but I would not worry too much about this since most post-editing software will correct barrel distortion.
Vignetting is evident in the new Nikon S 20mm lens, and like Barrel Distortion, is easily corrected using modern post-processing software such as Lightroom. As you know lightroom has "lens" profiles that automatically deal with imperfections. So I would not worry too much about distortion or vignetting.
So all this boils down to either buying a legacy lens, or the 20mm or 24mm f/1.8 S lens? Me personally, I would go for the newer S lens be it a 20 or 24, better lenses overall and no adapter required to use them.
Overall this Nikon 20mm f/1.8 is an excellent choice for your wide-angle needs, it has excellent build quality, excellent weather protection, and superior sharpness and image quality.- I recommend this lens for your Nikon Z system.