Crosshatch pattern on SII stack

[Wyvernp]

Hi All.

I'm having a strange issue with my SII stacks. I used the same batchpreprocessing script in PI to do Ha, OIII and SII all at 300s so also used the same dark frames. I cant seem to see this pattern at all within the individual subs although there was a lot of high level cloud when they were taken. The flats were taken this morning using the SGP flats wizard again using the same process as usual with a white lit ipad screen with a white tshirt over the scope. Target ADU was 22000. subs were 4.5 secs-ish. I also tried stretching the master flat and could not see this pattern.

Any ideas would be great.

 

[Wyvernp]

I have had it suggested that this could be an interpolation issue linked to low signal, I'm going to try a different method than lanczos. Failing that I will retake the subs with a much longer exposure.