The focal plane unit mounted in the test cryostat
The focal plane unit mounted in the test cryostat. The telescope beam enters the unit from below through the square aperture. The mask frame is centered on the two pins positioned at diagonally opposite corners of the aperture. The two lever arms lock the mask frame by pushing it against the two brown bearings. The white cylinders protruding from the bearings are made from Teflon and are spring loaded. When the mask is locked, the cylinders move downwards into the bearings. When the levers open, the cylinders push the mask frame upwards.