Issues with calibration frames or camera?

[Saturn488]

After processing my data from earlier this week I have some strange artifacts on my images.

Equipment being used:
- WO GT81 IV
- ASI1600MM Pro
- Baader 6.5nm LRGB Ha
- Pegasus Astro FlatMaster

Issue 1:
I get horizontal banding across the image. This can be seen especially in the Green and Blue channels. After doing some research online I found out it was the exposure time which makes it noticable. The lower the exposure the worse the bands (could be something to do with the refresh rate of the FlatMaster or interferance). I did many tests including:

- Taking flats pointed to the wall (no banding)
- Lowering the exposure (banding)
- Lowering the brightness and upping the exposure, can only do about 0.3 seconds (banding)
- Placing paper in front of the flat to reduce brightness and increasing the exposure (banding)

I have contacted Pegasus Astro, just waiting on a reply. I have seen the other forums with a similar issue but their resolutions are not working. Different profiles doesnt work. Increasing the exposure is not a solution because the image becomes over exposed.

Issue 2:
I noticed a line at the top and sides of my images. Using the green filter as an example, when processing with flats/dark flats and darks it isn't as noticeable.

I re-processed the image with no calibration frames and it looks a lot worse.

The first image is no calibration frames, the second with calibration frames.

Anyone seen this before?

I have also reached out to ZWO for assistance.

[Camelopardalis (Dunk)]

I’m going to suggest what Issue 2 looks like to me, but you will be able to say whether it’s relevant or not.

It looks like you’ve taken the shots over multiple nights and one set doesn’t align with the other set. This is why get get the smoother image inside the lines, while the outer edges are more noisy. This can be caused by not framing accurately enough over the different nights.

[Dave882 (David)]

I’m dealing with a very similar banding issue (1) to you. I have a el panel (cheapo Ali express job) and find that with very short exposures under 0.3sec I seem to get banding. I suspect it’s the control box (brightness adjuster) that may be doing it as the banding changes when it is adjusted).
I found that tinkering with the exposure times and going to adu 30,000 (about half of histogram) I could sometimes reduce or eliminate the banding. But also I found that if I blend flats of different exposures, or adjust the brightness of the flat field controller continuously while taking a set of 50flats I could get a much smoother field.
Obviously that’s a bit annoying but it’s my temporary work around at the moment….

[Saturn488]

Originally Posted by Camelopardalis

I’m going to suggest what Issue 2 looks like to me, but you will be able to say whether it’s relevant or not.

It looks like you’ve taken the shots over multiple nights and one set doesn’t align with the other set. This is why get get the smoother image inside the lines, while the outer edges are more noisy. This can be caused by not framing accurately enough over the different nights.

I had another look over my data and some of my nights I captured, framing was way off for some reason which will explain it!

It isn't a big deal as I can crop the image post-processing but next clear night I will recapture some channels and ensure its framed properly. I won't re-stack it but that sounds like it would be it.

Thank you!

[Saturn488]

Here is an example of the banding.

Lum Filter
0.18 seconds

If I increase exposure the bands get a little better but then I just get an over-exposed white image and I am back to square one!

I tried plugging the flat into another laptop so it's totally independent and not interfearing with any gear connected to the telescope's computer and still having the same issue.

I tried placing paper in front of the field flat but I get the same results. That would defeat of having the brightness levels and a field flat in the first place.

[Saturn488]

And here is a test I did with a tablet screen, no banding.

[Camelopardalis (Dunk)]

Originally Posted by Saturn488

I had another look over my data and some of my nights I captured, framing was way off for some reason which will explain it!

It isn't a big deal as I can crop the image post-processing but next clear night I will recapture some channels and ensure its framed properly. I won't re-stack it but that sounds like it would be it.

Thank you!

No worries! Yeah cropping is easy enough, especially when the target is smaller than the full frame