AbsolutelyN

Yes agree, maybe I'm digging too deep into the files and you are bound to find artefacts. I do stacking, DBE and star reduction in PixInsight, most of the rest in Photoshop. However I do challenge anyone to process the attached file (M31 stack of 4 hours with no flats) and not find the banding in the image - it's pretty prominent once you run a DBE and start to work on the image. Temp was -10 but I got the same at -20 a few days earlier so don't think it's temp dependant. I'm using 2 min exposures form Bortle 5. integration4.xisf

He is my master flat for comparison FLAT_CALIBRATED_BIAS_DARKFLAT_NEW.xisf

Brill thanks. Mine was a master flat but your single frame is very similar. If I apply a screen transfer function you exaggerate the fall off at the edges. Even more interestingly if I run a DBE and then STF you can actually just about see the same banding though not as strong. Probably because my flats are darker and it was a master flat. Maybe it is integral to the sensor after all if it's on more than one copy of the camera.

Pretty sure it's just the STF auto stretch exaggeratig the light fall off - if you look at raw de-bayered flat in PS it's similar to yours. I suspect if you do a STF autostrech in pixinsight you'll get similar.

I think it was mainly Topaz Denoise in Photoshop that I must have used too aggressively - probably amongst other things. Here is version two which I hope addresses some of the original issues. Sure there is still much that could be improved.

Thank you and yes completely agree - I've been working on a second version which has less aggressive sharpening. Always learning. great image.

My flats look similar in photoshop - screenshot has a STF stretch in PixInsight so is exaggerated. My darks are slightly darker I think.

Now that's what the flat should be like. What ADU are you exposing at? Although you can calibrate the banding out I do now suspect my camera is a dud. I've asked FLO about possibility of replacing it so will hopefully get it sorted.

Well I took new flats on my Esprit 80. Different computer, shorter better shielded USB 3 cable and different power supply. The banding is still there and clearly visible with nothing more than a STF stretch.

Will do, thanks for all the help.

That's an interesting point thanks. I guess I can test that by removing the camera and taking new flats with a short USB cable and laptop to eliminate anything that might be interfering in my current setup as that is a possibility.

Yes I sent ZWO screenshots of lights, darks, bias + flat. All I got was a one line response saying please calibrate with flats. And indeed calibrating with flats comes out with a pretty much spot on image. I don't see why I should need to use flats though. Very strange, I'm keen to know if anyone else has this banding or it's just my camera.

I don't do DBE on the flats 🙂 I only did so as I could not figure out where the banding was coming from and did a DBE to see if it was embedded in the flats too - which it is. Didn't think of moonlight but it can't be that as the flats have the banding and they were taken in daylight. Perhaps it does not matter as I know I can get rid of it now but it's taken me a week to get a usable image out of the camera, was almost at point of sending it back.

That's interesting. I was not planning on taking flats either as I've never needed them with the 1600MM on the RASA. However I found I cannot stack the images without flats as I get the same banding pattern shown above when I stack the lights which makes it impossible to use the camera without flats. No sign of the banding in the darks or bias. Contacted ZWO and they just said you need to use flats. Not sure if I have a dud camera or this is inherent to the chip. Lights without the flats look like this which is just unusable.

I'll have a go at some point over the next few days. It was a lot of firsts and rushed processing during a lunch break so can probably come up with something better. Suspect the biggest flaw in processing this is using Topaz De-noise. It's really good but often produces that painterly effect so need using very carefully.

I saw the Artesky adapter and was tempted but not planning on using filters. Currently using the Baader 7.5 mm T adapter. It would be good if Celestron just redesigned the front plate for better / repeatable image quality. As it is every time the camera moves it feels like pot luck on your star quality. It's done better than I thought though. Two questions though if I may? 1. Have you removed the optical window from the RASA? Feels like just an extra piece of glass in the optical train but I'm worried if I remove it it might make focal position different. 2. If you run a DBE on your flats do you get this banding pattern?

I readily accept your (not so) harsh criticism. That's a really good example and I intend to try to learn and improve.

Thanks Olly, that's really appreciated feedback. Sharpening and denoise was indeed Photoshop (not PixInsight) and I did wonder if I'd gone overboard on both sharpening and saturation. It was very hard to bring out the blues which is probably why they've ended up more purple than blue - first ever image I've processed from a OSC camera. As I mentioned earlier I think it's just one of those I probably need to revisit and process again with a fresh eye. I was just so relived to get the calibration sorted after days of issues with banding so probably went overboard in a few areas in my excitement!

Thanks Paul, that's much appreciated. I think I know what you mean. Perhaps more contrast in the arms and darkening the haze around the galaxy may improve it. I'll take a look at that and see what I can do. Sometimes it's best to process an image and then leave it a day and come at it fresh again. Much appreciated. Tristan

Thanks Dave. Wasn't expecting much with Moon so bright. Had awful results from these frames for last 5 days but finally figured out the calibration process.

True but I find you learn quicker if you are a harsh self critic. Saying that I don't think I can fix those stars as APSC is too big for image circle ... so perhaps best not to worry :-)

Thanks. I think the detail is simply due to the 8" aperture. The detail here is far more than I got with my Esprit 80 / 1600MM. Just wish the stars were pinpoint across the frame.

Finally got first image out of the new 2600mc. 4.3 hours on M31 with the RASA 8 - 128x 2 min exposures with 80% moon in bortle 5 at unity gain. Higher res on astrobin - https://www.astrobin.com/grod4i/ Re-processed to address aggressive noise reduction. Background is a bit lighter to try to pull out what I think is some faint HA in the background. Original:

Also the green / magenta bending doesn't seem match the bias or dark files - green/magenta seems more fixed width and regular Bias Dark:

Thanks. I can make my files available for comparison if needed (I'm worried I'm just not getting the calibration process right). All 120 sec exposures. I've not got any flats and have now removed camera for second set of darks. First darks were on well covered scope at night, second set with camera capped and covered in tin foil. Made no difference. Also have lights/darks at 100 gain and 0 gain and still have same results.