I have recently updated my camera to a used Nikon D800. My previous camera was a prosumer version that did everything for me. I am very much a beginner and I have an issue I want to resolve. Whilst testing the camera I set it up for continuous high-speed shooting with ISO set for auto. I then took 4 quick photos (less that 1.5 seconds) inside my house using the same subject in exactly the same light. The ISO change during the shoot dramatically resulting in photos that range from too dark to over bright. Given that the subject did not move, nor the conditions change, I don’t understand why the ISO changed so markedly. I am hoping this is a rookie mistake and I have confused the camera with conflicting settings. Any advice is most welcome. Thanks in advance.