A cryostat apparatus including a cooler configured to cool a cryogenic fluid. The cooler includes a cooler chamber disposed about a cooler axis. A magnet assembly is in thermodynamic communication with the cooler and is disposed about a magnet axis offset from the cooler axis. The magnet assembly includes a magnet housing and first and second annular magnet coils disposed about the magnet axis within the magnet housing. A viewing chamber is at least partially located between the first and second magnet coils, such that the magnet axis and a viewing axis perpendicular to the magnet axis both pass through the viewing chamber, with the viewing axis extending between the first and second magnet coils. The first annular magnet coil includes a first conical surface disposed about the magnetic axis and having minimum and maximum peripheries, the minimum periphery being disposed adjacent the viewing chamber.