Here is a quick comparison for the Nikon D850 vs Sony A7R II vs Sony A99 II high-end cameras with full-frame image sensors.

The Nikon D850 is a professional-grade full-frame DSLR which boasts of a 45.7-megapixel sensor and 4K video recording support. The D850’s body remains relatively unchanged from the D810 but there are some notable enhancements. See also Nikon D850 vs D810 article for the changes.

Sony A99II features a 42.4-megapixel full-frame CMOS sensor. The sensor allows for 12 fps burst shooting with continuous AF/AE and a top ISO of 102,400. The image processor offers 4K video recording and a 5-axis in-body image stabilization mechanism.

Sony A7RII is the world’s first back-illuminated full-frame Exmor R CMOS sensor with a resolution of 42.4 megapixels with 4K video recording. The new Sony A7RII boasts high speed AF response up to 40% faster than the original α7R thanks to 399 focal plane phase detection AF points.
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https://www.dailycameranews.com/2017/08/nikon-d850-vs-sony-a7r-ii-vs-sony-a99-ii-comparison/