TS, it is more important to understand what you need the camera to do before deciding on the actual lens you are going to buy. And if you intend to capture northern lights, make sure you devote part of the budget to a good tripod (they are not that expensive). Even though some senior members here are right that better camera bodies matter more when capturing astro-photos. Modern camera bodies are all pretty much capable enough to capture most of what you are planning to do. This is captured with an older Fujifilm XT2 and a small manual focus lens.