[sadia]

Recently I tried to do some narrowband imaging on Helix Nebula. Initially when I tried to push the data I found it to be quite noisy. I knew it’s a faint object but for 7hrs of data the noise level was quite unacceptable. But Once I tried to reprocess the data and paid some more attention I found that my STL is giving me some sort of vertical banding on each of my sub exposures in areas where s/n ratio is low which is the case for helix over Focal Length 1120 where except the central area rest is pretty much empty.

Exposures taken was 30mins . Calibrated against 100 bias, 30 dark, 30 flat. After doing few more test following are my finding

1. Vertical banding only appears when s/n ration is low. SII 3nm performs the worst.
2. Object occupying only part of the Chip shows the banding quite easily for rest of the area where s/n is low. Eg. Helix nebula at @FL1120
3. This doesn’t happen for objects which fills up the FOV giving higher s/n ratio across FOV. Eg. Horsehead nebula @ FL 1120 doesn’t show banding.
4. dos not happen for LRGB or I can't see it in LRGB
5. I don't see the this pattern in my master dark/ master flat/ master bias. Dark and Bias have their own pattern so it will be hard to isolate banding in them where Flat will be too bright to notice it.

Initially I thought I was doing something wrong so I retested this issue after making following changes but the issue persisted
1. Keeping STL power cable separate from other cables
2. No dew heater
3. Test was done @ -30C temp


I know some of you are using STL or have used it previously. Have any of you face anything like this? I will post some image tonight to show what I mean

Ok I am back home, and i can attach some pics. It's hard to see in isolated section but quite obvious once you minimize the image size.