My son sent me a link to an article on using the A7S for astrophotography. One thing I found interesting was a statement that ISO 400,000 was a great feature because it allows you to see and frame the Milky Way live in the EVF instead of having to review. One of these days I've got to check that out.
Sony a7S Astrophotography Review – Lonely Speck
Sony a7S Astrophotography Review – Lonely Speck