Hi John
would you just confirm for me, that when this option is checked on the "Settings" tab, that (a) a bias frame is actually subtracted from the flat to give accurate ADU, or (b) a bias frame is taken to adjust the exposure to reach the desired ADU value. I just really need to know whether I should use a bias frame when calibrating/combining to produce my master flat.
thanks

Martin
P.S Happy Christmas

Hi Martin,

No a bias frame is NOT subtracted. The bias level is measured and added to the target ADU to insure a result closer to the target ADU when the exposure is taken. This is necessary as some cameras have average bias levels as high as 4000 ADU!

In reviewing the help file, I can see that the description of auto bias is not clear on this point and I will correct that in the next maintenance release.

Merry Christmas!

Thanks John