SHTSTAT of SKYFLAT

仿出来的SKYFLAT（不带快门效应）的快门状态是“F”： SHTSTAT = F / shutter status, T=open, F=close
SHTOPEN0= '' / shutter open time (start, UTC)
SHTOPEN1= '' / shutter open time (end, UTC)
SHTCLOS0= '' / shutter close time (start, UTC)
SHTCLOS1= '' / shutter close time (end, UTC)

SKYFLAT（不带快门效应时）的快门应该也是打开的。