Amy Davies of Photography Blog has issued her review for the Sony FE 100-400mm f/4.5–5.6 G Master lens. Analyzing the focal range, distortion, bokeh and sharpness, PhotographyBlog gives the lens a 4.5/5 stars and has a suggestion for photographers: 

"If you’re a professional photographer looking to move to the Sony system, it’s also going to be an essential piece of kit for those that photograph distant subjects."

Sharpness tests were run on the lens at 100mm, 135mm, 200mm, 300mm and 400mm and the results were consistent – "Bearing the name G Master signifies that this lens is going to really deliver, especially when it comes to sharpness. That is borne out by both the sharpness tests we have carried out and the more normal real-world scenarios we have been using it in. It is capable of delivering superbly sharp and well-focused images, time and time again, with a hit rate which is very attractive to those photographing split-second moments."

PhotographyBlog also has a recommendation for using the lens with various cameras:

"Although you can combine this lens with any of Sony’s e-mount cameras, it is definitely most at home with the α9, where you can use it in conjunction with 20fps silent shooting for some really special results. That said, if you own another one of Sony’s cameras, such as the α7R and are looking to produce some highly detailed wildlife work, it would also be an excellent choice."

"Overall, the Sony FE 100-400mm F4.5–5.6 GM OSS lens is a fantastic lens which is capable of producing some superb images and in conjunction with the α9 is a delight to use." Amy Davies, Photography Blog

See the full review from Amy Davies at PhotographyBlog.com