Just at thought, I would just check the filter. I had one large mote (easily visible with my eye) that was stuck on the filter that didn't completely go away with my flats. After careful removal from the filter glass, all was well again.
Cheers,
Dave
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James Peirce:
Jon Rista:
I wonder if the camera uses a different kind of readout mode for shorter exposures. Something more akin to a video-style readout, which may lead to the banding. It is the 294...that sensor seems to have a multitude of little issues, kind of like the Panasonic M, which also had problematic readout issues at certain exposure settings.
Maybe… it’s an interesting thought. I couldn’t suggest a better theory. Unless maybe some aspect of the banding behavior becomes a lot more stable under longer exposures and hence calibrates more reliably for some other reason.
I did eventually get both cameras (MC now sold, MM I ponder parting with) performing reasonably. But I had to jump through hoops to get there. I don’t know if it’s a sensor issue or what, but they’re not cameras I’m fond of recommending. By contrast my experience with the 2600 is always everything calibrating so splendidly. I also always had smooth calibration with the 1600MM, and it wasn’t the cleanest sensor.
The Panasonic M (in the ASI1600s) had bias stability issues with exposures, IIRC, under around 0.3 seconds. I did extensive testing when I ran into problems using bias frames, and found that there was a random gradient in every frame for exposures under 0.3 seconds. From 0.3 or longer, the bias signal was fine. That sensor also had a pattern dependency on gain. If you changed gain, or I think the USB traffic setting, the banding pattern in the bias signal and darks would change. There was no way to get back to any previous pattern, even restoring the same gain. The sensor has other issues as well.
I generally had fine calibration, so long as I never used an exposure shorter than 0.3s. If you use dark flats, that might be a reason why you've never encountered the bias instability issue. In any case, as you mentioned with the 2600, there are much better sensors out there than the IMX294 or Panasonic M. These days, I'd say, save yourself some hassle and headache, if you can afford it, and get a sensor that has no glows, no instabilities, etc. ;)
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I managed to grab some more longer length flats and there was no difference - in order to keep the file size small I just grabbed a Screen Shot of the Master light as I brought it into PixInsight after WBPP - here is a part of it:
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Maybe these help too? I've treid other variations but these usually work well:
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Maybe these help too? I've treid other variations but these usually work well:
Hmm...that "Optimize Dark" setting... That is dark scaling. That can be problematic. You seem to have just 300s darks, but have 4s flats, which would result in dark scaling, if you are indeed calibrating them with the master dark. I would try to turn off that setting, and see if it helps at all.
Also, not sure what WBPP does here...does it try to calibrate the flats with a master dark, ALWAYS? Or, does it only calibrate with the master bias? Do you have any control over that? I would say, if you can just calibrate the flats with the master bias to start, and skip using the master dark with the flats, and see how that goes, that might be optimal.
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Thanks I'll try that - Running another right now;
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There also seems a little bit of positioning error as seen by slight differences in correction between one edge of the artifacts and another. Knowing that you took your flats right after L frames - could there be some issue with movement in the filter wheel due to change in position of the scope between lights and flats?
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Maybe these help too? I've treid other variations but these usually work well:
Try to do everything without recourse to WBPP and no scaling of darks, this is definitely no no.
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Also, some filter wheel electro-magnetic fields make dust levitating and the thing keep shifting. But I'd compare the flats against the unprocessed lights.
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I ran it without the optimize dark - result is the same ; weird as I use these settings for data from my other scopes and all is well with them.
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Arun H:
There also seems a little bit of positioning error as seen by slight differences in correction between one edge of the artifacts and another. Knowing that you took your flats right after L frames - could there be some issue with movement in the filter wheel due to change in position of the scope between lights and flats?
Yeah that was my original thought too; I guess it's possible that the wheel is loose or something but the others (especially SHO) are all good.
I guess I'm probably going to have to dismantle and investigate further?
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Mirror flop might make everything more difficult but not sure whether this is happening here.
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Yeah that was my original thought too; I guess it's possible that the wheel is loose or something but the others (especially SHO) are all good.
These subtle differences will not be evident in narrowband flats. I can't describe to you the vast difference between the robustness of narrowband flats versus "L" flats correcting L frames taken in light pollution. It also doesn't help that you have no nebulosity in that area.
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andrea tasselli:
Also, some filter wheel electro-magnetic fields make dust levitating and the thing keep shifting. But I'd compare the flats against the unprocessed lights.
When I do this it gets even stranger because the majority of motes etc. are cleaned up OK and only a few remain and they seem no more intense than the ones that correct properly
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andrea tasselli:
Mirror flop might make everything more difficult but not sure whether this is happening here.
Could mirror flop
Could mirror flop affect the immediate dust motes though ? Wouldn't that just affect the target position and focus ?
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Jon Rista:
Timothy Martin:
Light pollution really wreaks havoc on how lum flats correct things. I never figured it out. I finally went remote to solve the problem. But even then, when the moon is out, I might get lum subs where I can correct the gradient, but then the flats no longer work as well--especially the luminance flats. One thing that did help is that I went from taking 20 flats to 50. So I would recommend trying more flat subs, or as others have suggested, lengthening the duration of the flats.
Keep in mind that an LP gradient is not, and never has been, something that flats will or could ever correct.
Flats will only correct the intrinsic field shape and structure as dictated by your scope and image train. Light pollution is an external pollutant signal, and flats have never been capable of correcting that. Hence the reason why we have gradient correction/extraction processes in our pre-processing tools (GraXpert or the new GradientCorrection tool in PI).
If you are hoping that flats will or could correct LP gradients, then know that its never been the domain of flats. Even at a dark site, you can still have gradients. I imaged a lot at a dark site for several years, and often ran into moderately to very high Airglow, which can introduce a notable greenish or brownish tint and often gradients into the images. Additionally, if I tracked on any particular target for too long, I would sometimes run into the upper reaches of the Denver LP bubble, which was on the western horizon. Gradients and their correction are often a real-world fact of life with astrophotography, and have never been the domain of flats. Flats should try to properly model the optical space, but nothing more.
I completely understand this. My point was that flats, particularly on the lum filter, don't work as well at removing dust motes, or even correcting vignetting, in high Bortle areas or at dark sites when the moon is out.
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Could mirror flop affect the immediate dust motes though ? Wouldn't that just affect the target position and focus ?
It would affect the shading of the motes and the overall vignetting. Not by much but enough in high LP situations or with high Moon. You could use a LP filter and possibly get away with these issues.
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Frankly I am having the same problem with m L filter on my 6200mm pro and I have no idea if it is reflection, light leak, or the something else. I have taken anything from 1s to 6s flats, and I have tried anything from 1/3 to 1/2 the histogram. Reshot my Bias, Darks, made sure gain and offset is equal accross everything, even painted the inside of the focuser. Haven't tried sky flats yet but I might have to try that next.
Narrowband is fine. RGB is mostly fine. L is just terrible. (And it is a Chroma filter)
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andrea tasselli:
Could mirror flop affect the immediate dust motes though ? Wouldn't that just affect the target position and focus ?
It would affect the shading of the motes and the overall vignetting. Not by much but enough in high LP situations or with high Moon. You could use a LP filter and possibly get away with these issues.
I actually use an L-Pro as my Luminance filter for that reason ;
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Ashraf AbuSara:
Frankly I am having the same problem with m L filter on my 6200mm pro and I have no idea if it is reflection, light leak, or the something else. I have taken anything from 1s to 6s flats, and I have tried anything from 1/3 to 1/2 the histogram. Haven't tried sky flats yet but I might have to try that next.
I wasn't any better off with sky flats; they produced the same issue. I've now tried between 0.25 and 4 seconds for the L flat with no real difference. I've got the 6200 mounted directly to the filter wheel and all else seems pretty light tight.
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I actually use an L-Pro as my Luminance filter for that reason ;
*At least you're covered on that side. If you can post an unprocessed light and the master flat that might help understanding what is going on.
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andrea tasselli:
I actually use an L-Pro as my Luminance filter for that reason ;
*At least you're covered on that side. If you can post an unprocessed light and the master flat that might help understanding what is going on.
Can I post a Sendthisfile link ? Can't post those file sizes here.
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Timothy Martin:
I completely understand this. My point was that flats, particularly on the lum filter, don't work as well at removing dust motes, or even correcting vignetting, in high Bortle areas or at dark sites when the moon is out.
How are you illuminating your flats? Is it with some kind of panel? If so, have you (and others in this thread having troubles) ever tried with a clear, blue, DAYTIME sky?
I used to use either a white illuminated wall, or a TV or computer screen with a white background, as panels. I always had one problem or another. I eventually tried sky flats at dusk, which was better, but you have gradients in the flats, sometimes stars, etc. When I switched to using the daytime blue sky, my flats started performing optimally.
I think there can be wavefront differences with a panel light source at the aperture, vs. a light source at for all intents and purposes "infinity" from the aperture. A daytime blue sky is effectively at the same distance, or close enough from a wavefront standpoint, as light pollution at night.
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Jon Rista:
How are you illuminating your flats? Is it with some kind of panel? If so, have you (and others in this thread having troubles) ever tried with a clear, blue, DAYTIME sky?
I am using a large 24" variable LED panel BUT I have also tried sky flats and concluded that the LED flats were performing better;
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10.10
8.59
1.51
11.91
7.72
11.04
6.96
