Steve Spencer
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Ripolini wrote:
By looking at the tests linked above, I understand that the Sony 20/1.8 GM is sharper; that's different from saying that the Z 20/1.8 isn't sharp. Simply, it isn't as sharp (according to those tests), in particular at the wider apertures.
According to the same tests, the Z 20/1.8S suffers from coma (see here) even at f/2.5, so I wonder how some people report "excellent coma control". Did Lenstip test a faulty Z 20/1.8S sample 
There are tests, measurements, images ... and there are words, chatters, etc. ...
If you compare the Z 20 f/1.8S and the Sony 20 f/1.8 G, both lenses are excellent, but both lenses have their weaknesses. The Sony has outstanding center sharpness even at the widest apertures, but until f/2.8 its edge and corner sharpness lags the Nikon Z lens. Another way to say this is that the Nikon lens at wider apertures has more even sharpness across the field but does not reach the peak of sharpness of the Sony lens in the center at wide apertures or even fully at stopped down apertures. Now on this issue of which sharpness profile one prefers, I prefer the Nikon profile as I dislike big differences in sharpness across the field (at least for a lens with this wide a focal length I can even appreciate better center sharpness with reduced sharpness at the edges and corners in a portrait lens). But sharpness isn't everything. Other characteristics matter.
The Sony has excellent coma control and beats the Nikon in that regard and this would be particularly important for those that shoot astrophotography. In contrast the Nikon has better resistance to flare than the Sony and that may be particularly important to those who shoot landscapes. Personally, I think the Nikon lens is a little better for landscapes than the Sony (at least the way I shoot landscapes) but the Sony could be better for other types of shooting (e.g., if I shot music in a lot of dark nightclubs that would play to the Sony's strengths and mitigate its weaknesses). Both are good general purpose wide angle lenses, but neither, IMO, is a great astro lens (the Nikon has too much coma at wide apertures, and although the Sony does better with regard to coma it has weaknesses at edge and corner resolution).
And that is just at 20mm, suffice it to say that in my view any one who says look at these reviews at the one site and focuses on just resolution is engaging in a shallow analysis. When you really look and do careful comparisons there are pluses and minuses to all the lenses mentioned and these reviews don't even touch on other important ones (e.g., focus breathing if you are going to shoot video). In my view, the f/1.8 S lenses are all very good lenses, but not without their weaknesses. The important thing to know is what the weaknesses are and how they will impact your shooting. Only then can you know whether the Sony version might be better for you or not. The Sony G lenses in particular are quite good lenses. The Sigma i series lenses are also quite good lenses. Whether those lenses are better for you than the Nikon f/1.8 S lenses, however, depends in my view on a much more nuanced analysis than simply looking at resolution testing of just one lens from each brand at one web site.
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