I would second either light leak (I've experienced light leaks from the focuser drawtube myself), reflections (light entering focuser drawtube not from the secondary mirror), or some optical element shifting.
If you're extremely confident that it isn't a light leak or reflection you can test to see if it's some sort of flexure of the secondary or primary by taking flats and lights at zenith and looking at the result vs flats at zenith and lights lower on the horizon.
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I would second either light leak (I've experienced light leaks from the focuser drawtube myself), reflections (light entering focuser drawtube not from the secondary mirror), or some optical element shifting.
If you're extremely confident that it isn't a light leak or reflection you can test to see if it's some sort of flexure of the secondary or primary by taking flats and lights at zenith and looking at the result vs flats at zenith and lights lower on the horizon.
*I will check it again of light leaks, but I am very confident. I can do 60 sec exposures during daylight with closed lid and have a dark frame.
I got a f3 system. Any shifting in mirror elements would be a huge change in star shape, but they are always fine, no matter what direction I am looking at.
I did some testing tonight and tried my color camera (same sensor / size) I did noticed something strange, with both cameras.. when I am taking 0.19 sec exposures the vignetting looks fine and I got a ADU as expected. When i do 0.2 sec exposures, the ADU is increased like it should be. When I do 0.21 however anything goes wrong. The ADU is highly increased and the vignett shifts... I think both touptek cameras got a readout problem!  
I am testing if this is happening to the ZWO 2600mm too. If so there is maybe something wrong with cable or power management. This Problem also apears in other programmes. And on the sky! So no flat pannel here
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I would second either light leak (I've experienced light leaks from the focuser drawtube myself), reflections (light entering focuser drawtube not from the secondary mirror), or some optical element shifting.
If you're extremely confident that it isn't a light leak or reflection you can test to see if it's some sort of flexure of the secondary or primary by taking flats and lights at zenith and looking at the result vs flats at zenith and lights lower on the horizon.
*I will check it again of light leaks, but I am very confident. I can do 60 sec exposures during daylight with closed lid and have a dark frame.
I got a f3 system. Any shifting in mirror elements would be a huge change in star shape, but they are always fine, no matter what direction I am looking at.
I did some testing tonight and tried my color camera (same sensor / size) I did noticed something strange, with both cameras.. when I am taking 0.19 sec exposures the vignetting looks fine and I got a ADU as expected. When i do 0.2 sec exposures, the ADU is increased like it should be. When I do 0.21 however anything goes wrong. The ADU is highly increased and the vignett shifts... I think both touptek cameras got a readout problem!
I am testing if this is happening to the ZWO 2600mm too. If so there is maybe something wrong with cable or power management. This Problem also apears in other programmes. And on the sky! So no flat pannel here
This ADU issue is actually really interesting. I have a risingcam 571 and have never encountered this issue. I know someone in England with one as well and we were having a conversation on this exact issue just 4 days ago. When he took flat frames at .2 seconds or lower his illumination was fine - when he took them at .2001 - 10 seconds he had offset illumination and hugely increased ADU. This issue wasn't present in his dark/bias friends. Past ten seconds his flats went back to normal.
Example - .2 on left and .2001 on the right:
https://cdn.discordapp.com/attachments/247352166078087178/1161343974506762331/image.png?ex=6537f4dc&is=65257fdc&hm=2743cafa1505e5cd8077eb5cd2e42399b742671c0b07fe7df9c01b75c1983642& |
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I would second either light leak (I've experienced light leaks from the focuser drawtube myself), reflections (light entering focuser drawtube not from the secondary mirror), or some optical element shifting.
If you're extremely confident that it isn't a light leak or reflection you can test to see if it's some sort of flexure of the secondary or primary by taking flats and lights at zenith and looking at the result vs flats at zenith and lights lower on the horizon.
*I will check it again of light leaks, but I am very confident. I can do 60 sec exposures during daylight with closed lid and have a dark frame.
I got a f3 system. Any shifting in mirror elements would be a huge change in star shape, but they are always fine, no matter what direction I am looking at.
I did some testing tonight and tried my color camera (same sensor / size) I did noticed something strange, with both cameras.. when I am taking 0.19 sec exposures the vignetting looks fine and I got a ADU as expected. When i do 0.2 sec exposures, the ADU is increased like it should be. When I do 0.21 however anything goes wrong. The ADU is highly increased and the vignett shifts... I think both touptek cameras got a readout problem!
I am testing if this is happening to the ZWO 2600mm too. If so there is maybe something wrong with cable or power management. This Problem also apears in other programmes. And on the sky! So no flat pannel here
This ADU issue is actually really interesting. I have a risingcam 571 and have never encountered this issue. I know someone in England with one as well and we were having a conversation on this exact issue just 4 days ago. When he took flat frames at .2 seconds or lower his illumination was fine - when he took them at .2001 - 10 seconds he had offset illumination and hugely increased ADU. This issue wasn't present in his dark/bias friends. Past ten seconds his flats went back to normal.
Example - .2 on left and .2001 on the right:
https://cdn.discordapp.com/attachments/247352166078087178/1161343974506762331/image.png?ex=6537f4dc&is=65257fdc&hm=2743cafa1505e5cd8077eb5cd2e42399b742671c0b07fe7df9c01b75c1983642&
Thank you so much for that information!!!! I was hoping someone has this proboem too... i was wondering if iam just dump or something. I will figure things out. Would be insane if many touptek cams got this problem
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I dealt with this exact issue for years as well. I chased every possible location for light leaks, 3d printed mirror cell covers,dew shields, electrical tape, laser cut aluminum focuser support brackets, flocking, Black 2.0 paint, upgraded spider and focuser because I thought something was moving, etc. The issue even followed me when I got a carbon fiber ONTC. No matter what I did I always had the embossed donut artifact in my images. I didn't have issues with SHO but only LRGB.
Like was said above, eventually I found a thread about someone dealing with the same issues that advised taking very long flats. I started taking 10 to 15 second flats and the issue finally disappeared.
Good luck
Mike
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