Strange appearance of Oiii MasterFlat

[XCalRocketMan]

Just wondering if anyone here can give me some guidance on a potential issue I might have with my Astrodon Oiii 3nm filter. All my masterflats look as I would expect them to look except for this Oiii. It has a darker oval surrounding the center of the FOV and light and dark bands emanating from the top left across the FOV. Has anyone ever seen something like this? Should I be concerned about it? I thought maybe the filter (31mm unmounted) is possibly being pinched because the 3 screws holding it in the filter wheel may be too tight.

[STEVE333]

I have a 31mm unmounted Chroma 3nm Oiii filter. The unstretched MasterFlat looks very normal, but, the stretched version is very strange looking (stretched image below) and took my breath away. I thought for sure there was something wrong with the filter.



However, the MasterFlat for the Oiii data works fine and none of the MasterFlat "structure" appears in any of the calibrated images

Don't know if this helps you or not.

Steve

[XCalRocketMan]

I have a 31mm unmounted Chroma 3nm Oiii filter. The unstretched MasterFlat looks very normal, but, the stretched version is very strange looking (stretched image below) and took my breath away. I thought for sure there was something wrong with the filter.



However, the MasterFlat for the Oiii data works fine and none of the MasterFlat "structure" appears in any of the calibrated images

Don't know if this helps you or not.

Steve

Yeah, the calibrated images look fine. I was just a bit taken aback at what the flat looked like. I guess it's not really a problem (at least it's nice to see someone else has a similar looking stretched Oiii Master Flat :Think: )

[Stuart]

My guess is that it just be an artifact of the autostretch, because it's trying to stretch minor differences in the data.