Think I have found the cause of my problem.
Three seeing profiles attached for T CrB with S30.
Stack from February 2025.
Stack from April 2026.
Single sub from April 2026.
Looks to me like ZWO have screwed up their stacking algorithm, the April
2026 stack has saturated, 16 bits so maximum ADU is 65,535.
Note the peak ADU for the stack from Feb 2025 is similar to a single
sub from April 2026.
So the good news is that my data might be recoverable, the bad news is
that I am going to spend a lot of time stacking subs in an external
program.
Stop press, in La Palma, ran S30 on T CrB overnight, 2,134 10 sec subs,
again stack is saturated, individual subs look OK.
