A salient question when considering a specialty camera like the 20.6-megapixel Nikon D5 is how much better its high-ISO performance is versus a camera optimized for high resolution at lower ISO values such as the Nikon D810.
Is the Nikon D5 actually better at high ISO than the D810, and if so, how is it better and at which ISO values?
The 36-megapixel Nikon D810 debuted in early summer 2014, about two years prior to the April 2016 debut of the Nikon D5. We therefore might expect that nearly two more years of advancement in sensor technology along with a 20.6-megapixel resolution would provide a clear win for the Nikon D5 at high ISO values.
For the same enlargement factor, is high ISO performance better? It is an error to compare noise behavior on a per-pixel basis. What matters is the noise and color rendition and black rendition at any given reproduction size, such as a print of any given size. Accordingly, this evaluation compares the D5 and the D810 cameras using the same lens and same exposure at the same image size.
Includes image sizes up to 5974 pixels wide (about 24 megapixels).
There are other considerations too: the higher resolution of the Nikon D810 is a form of oversampling, which has its own benefits, as the comparison shows. Image quality is a sum total, not a any one factor.
Shot with the Zeiss Milvus 85mm f/1.4.