Nikon has issued a service advisory for its D810 DSLR. According to the company, some models can produce white spots during long exposures or when shooting in 1.2 mode.
If you want to see if your D810 is susceptible to this malady, head on over to the Nikon website, plug in your camera’s serial number and hold your breath. According to the Nikon EU site, cameras “with a black dot on the tripod socket” have already been addressed, so if your camera has that dot it’s safe even if its serial number comes up as problematic.
Nikon will fix any afflicted D810s free of charge.