Help diagnosing lines in Flats

[Rob Hamlin]

Hi All

Im running an Sbig STF8300M.

Am finding my HA, SII and LRGB flats have a grid pattern running through them.

OIII flats quite oddly, seem far smoother and dont have the issue. Somewhat baffled about this.

The image ive attached below shows what I see on-screen.

The grid pattern seems quite clear and im not entirely sure how big a problem this actually is.

Any feedback thoroughly appreciated

With thanks

Rob Hamlin

[glend (Glen)]

How are you shooting your flats? Looks like a cloth weave pattern.

[multiweb (Marc)]

Could be a reflection of the micro lensing on the chip when the light source for the flat is too bright and the exposure too short. Try to dim the light and lengthen the exposure see if it looks better.

[RickS (Rick)]

What ADU levels are you getting in the Ha and Oiii flats?

[gregbradley]

Did you subtract a bias or flat dark from the flat? Its fixed pattern noise.

Greg.