If you were hoping that Sony had finally completely removed the long-exposure noise reduction that causes its high-resolution a7R cameras to “eat stars,” you’re going to be disappointed. According to Jim Kasson, the Sony a7R IV eats stars to about the same degree as the a7R III.
Over on his blog, Kasson posted dark field spectra results for the Sony a7R IV at 1/8000 of a second, 2.5 seconds, and 3.2 seconds. The dark field spectra for each color “plane” at 1/8000 and 2.5 seconds look mostly flat: in other words, the way they’re supposed to.
But once you hit 3.2 seconds, as Kasson puts it, “all hell breaks loose” in every channel, and it’s particularly bad in the blue channel. You can see all the charts over on Kasson’s blog.