In his review of the Sony FE 12-24mm f/4 G for PhotographyBlog.com, Mark Goldstein tests the sharpness of the lens at 12mm, 18mm and 24mm.
"The Sony FE 12-24mm F4 G is a very good, if pricey, ultra-wide-angle zoom lens for Sony α9/α7/α7R II/α7S full-frame cameras. It delivers excellent sharpness in the centre of the frame almost throughout the full aperture and zoom range and also performs very well at the edges of the frame too."
In addition to the image sharpness through the full zoom range, Goldstein credits the lens' 4.5-star rating to its quick auto-focusing and build quality.
"The Sony FE 12-24mm F4 G offered pleasingly fast, quiet and reliable auto-focusing on the α7R II that we tested it with, intuitive manual focusing and very good build quality, plus it's usefully weather-tight too."
See the full review, along with Goldstein's sample images at PhotographyBlog.com.