Brian is thinking about changing camera systems from the Canon EOS Rebel T3i to the Sony Alpha 6000. Leo says that mirrorless cameras have really taken off because their quality has improved and they are smaller. It has a similar APS-C sensor as the Canon T3i. Leo says if he can swing it, pay the extra and get the Sony A7II or A7S with its full frame sensor.
Leo also recommends micro 4/3s cameras like the Olympus OM-D. But that's even smaller than APS-C. If he's taking a lot of astral photography, a full frame sensor is his best bet, especially with a fast lens.