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I have been using APP for a few years now and I love it. I have been using a ZWO 183MC Pro and recently got a ZWO 183MM Pro. I tried my first integrations and in tab 0 I left pattern: supported, algorithm: adaptive airy disc, unchecked force Bayer/X-Trans CFA, unchecked use camera white balance, and unchecked use camera color balance. In tab 6 I did 1st degree LNC and 5% MBB.
The individual stacks look good to me.
I then normalized these files and did RGB combine. This looked OK to me.
I then brought it into HSL selective color, made some adjustments, saved and brought it into GIMP, saved a TIF file to bring into Starnet to remove stars. At this point I noticed a grid pattern in the photo. I hope you can see it in the jpeg. Going back to have a look I think I can barely see a pattern through the stars in the original RGB combine.
I tried the stacks without LNC and MBB and got the same thing. I then tried stacks with Bayer, camera white balance and camera color balance checked. Same thing. Any ideas what I may have gotten wrong. I have never had this issue with the color camera. And I do not notice a pattern in the individual stacks. ZWO website does mention a grid pattern with solar Ha imaging but I have not heard anything about mono imaging. I did upgrade last week to version 2.0.0 beta 26. I did do another RGB combine and HSL selective color with less adjustments that was better but I am just wondering if you might know what is causing this pattern.
Thanks, Tom
Hi Tom, @tfergu01
Do I understand correctly that this is shot with your new monochrome camera? If so, the settings in 0) Raw/Fits will not matter, these are for color camera's essentially 😉
I see the grid pattern in the starnet result, it looks a bit weird. Maybe Starnet is not performing as expected here, I am not sure... Did you try Drizzle integration or not?
Mabula
Hi Mabula,
Yes, this is with my new monochrome camera and I did not drizzle. I started looking at the individual frames and this is what I found.
Ha flat frame-I think I see a pattern.
Zoomed in 150% I don't see an obvious pattern.
OIII flat frame-I don't see a pattern.
Zoomed in 150%-still no pattern.
SII flat frame-I definitely see a pattern.
Zoomed in 150% I still see a pattern.
The pattern in the flats looks smaller than the stacked version. Should I try processing without the flats and see if I get the same result?
Thanks, Tom
Hi Tom @tfergu01,
Ah, that really helps, so we need to understand what is happening with your flats then.
First of all, yes, make stacks without the flats and see if that pattern is gone, then we know for sure the problem is in your flats.
If the flats are the culprit, how do you make them? What exposure time do you use? And do you use bias or darkflats for your flats? Which exposure time do the bias / darkflats have?
Mabula
Hi Mabula,
I do flats using a light panel I bought from Illumiglow. Then dark flats with same exposure time. All using NINA and trying for 1-5 seconds exposure time. My Ha flats were 1.30 sec. My OIII flats were 1.72 sec. My SII flats were 2.72 sec. I tried some flat frames with the SII filter against a white board and got the same pattern. If there is a pattern in the flat frame, should the dark flat correct it?
So I tried stacking without the flats and dark flats and I think it worked better. I stretched the photos to see any patterns and I see a bit of horizontal banding but not the grid pattern. I think more aggressive dithering might help this.
Starless
So I processed further in GIMP.
Thanks, Tom
Hi Tom,
The strong grid pattern is a known characteristic of the mono imx183 small pixel sensor that you have, in the MM and GT camera varieties. ZWO replaced some of these cameras where the issue no longer shows. It was first noticed in H alpha solar imaging, showing very strong grid pattern in small (0.1 nm or less) bandwidths.
I can see it in both the H alpha and the SII flats you show above, with a stronger stretch, you might be able to confirm. In any case, I would contact ZWO, they are aware of this issue and should arrange replacement.
CS,
Hi Kullumm,
Yeah, ZWO's website mentions the solar imaging pattern but i had not heard of an issue with deep sky imaging. I will check with ZWO. Thanks for the info.
Tom
Thanks Kullimm for your input here, in that case, yes, contact ZWO for replacement 😉
But also, more dithering should really help as well ! Try to dither with at least 4 pixels or more if your setup allows. Even with camera's without this issue, bigger dither steps will reduce noise more quickly in general ! because many sensors have noise patterns on pixel scales that are 2-4 pixels large, even the newest cmos camera's. We know this from noise reduction statistics compared to the dither step size 😉
@mabula-admin So I contacted ZWO and sent them the photos along with a dark frame they requested at 60 sec and 0 deg C. They did not see any issues so would not replace the camera. At this point I do not think it is an issue with APP so unless someone discovers a solution we can consider this done I suppose. I do wonder if it may have something to do with less light pollution getting through with the 6nm filters. When I try an optimal exposure calculation other people have devised I think I get somewhere around 2000 seconds. That won't work. I tried a mono shot of a galaxy with a luminance filter and did not notice any patterns so could the pattern noise be getting drowned out with more light pollution through the luminance but not the narrowband filter? I may have to post on Cloudy Nights and see if someone there has seen this issue.
Thanks for your help Mabula and Kullumm, Tom
