› Forums › Spectroscopy › ISIS flat field vertical gain correction tool › Background sky level
2 October 2019 at 12:21 pm
#581428
![](https://britastro.org/wp-content/uploads/2018/11/picture-219-1541235408-80x80.jpg)
Participant
Hi Robin,
The level of the background sky in my LISA images is very flat in the Y direction, much as you have found. The flat lamp image as recorded is not flat, probably due to the different light path from the lamp into the spectrograph. So I think applying the vertical gain correction results in a better flat correction.
David