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This is interesting, I seem to have a very similar problem which started in the last few weeks. I have a Skywatcher Esprit 150 and also use an ASI533. The image below was taken without filters. I re-took the bias, flats and darks in the last couple of days. The flat exposure was 3 seconds, all the calibration images were at gain 100 (unity). The problem goes away if I don’t use darks. Using the light pollution tool will also completely remove the gradients. Will be very interested to find out the issue.
First of all thanks @mabula-admin for your patience and kindness.
I have been taking flats for 2 years with following method that never created me any sort of problems: i usually use a led Lacerta panel, same gain and temperature as lights, 2 seconds exposure, around 30.000 ADU on Asiair Pro. 50 flats calibrated with 2 s exposure dark-flats (same temperature and gain as flats and lights as well). Then i'm used to use Bad pixel map previously created with darks (in this case, 35 darks, same temp and exposure as lights).
Hi, I just took the camera and re-made the darks in a completely dark room. When I reprocessed the image in exactly the same way but with these darks the problem went away. The issue appears to have been light getting in to the camera when I was taking the darks. It looks like ippiu has a different issue. Hope it gets resolved!
@ippiu Last night I switched my ASI6200MM from gain 100 to gain 0 and offset 48. Then I shot 90 images of 60 seconds each of the Gum supernova remnant (I live in Chile) using my SharpStar 94EDPH with F/4.4 flattener/reducer and a ZWO Ha filter. I also shot 59 dark of 60 sec and bias frames of 0.01 sec and today I shot 27 flat frames of 1.2 sec and 59 dark flat frames of 1.2 sec. All at temperature -10º C. The peak of the histogram of the flats is almost completely to the right but not clipped:
The result looks very good with all vignetting completely gone:
The glow to the lower right is Ha emission and not amp glow or another artefact.
FYI I have asked Mabula to take a look at the files you uploaded.
61.500 ADU is quite high, almost near the maximum of 65.535....
Yes it is high but the point is that it is not too high. The histogram is not clipped on the right. This way almost the maximum dynamic range and full well depth are used.
Yes, i've already tried with no darks, with no success. Rather, it's worse than with darks...
Pity. OK, let's wait for Mabula to have a look at your data.
I am studying Ippiu's data at the moment. I don't have a complete explanation yet, but I do think that something is not right in terms of the actual data.
This is what I get in APP 1.082, at first sight it looks pretty okay. This is 5 lights, 5 darks, 5 flats, 5 dark flats. The fits header shows the same sensor gain and offset, so all seems to be okay there as well:
Only when i boost the saturation and stretch very strongly, I see the problem arise:
Now, to me..., that looks like a clear data problem in the red and blue channels... the noise in red and blue is simply much !!! higher and those channels are not corrected wel in terms of flat-field correction. We can see evidence of this in the integration file by studying the histogram wings on the left side of the peak:
I created this stretch by manually adjusting the Black point with the Black slider and lowering the ST slider (making the stretch stronger). Clearly, the Red and Blue channels have a problem, green looks well corrected though. Red has the biggest problem...
Now it becomes more interesting if we look at a single dark or dark flat, strongly stretched. THe histogram is very important here to check! (do so with saturation turned off in the preview filter)
A single dark flat:
A single dark:
Look at the histograms in these screenshots:
2 big problems are shown in the histogram:
1) Red and Blue are in no way balanced with green... the magenta areas in the histogram show that.
2) We don't see a nice noise pattern which we would expect in these dark frames, the gaussian noise distribution is damaged severly. The spikes in the histogram show bad camera or sensor behaviour to me.
Now, I don't know if this is normal for an asi533, I don't have one myself. It would be very interesting now, to see a dark from the asi533 shot with a different capture program than the asiair software. If that looks the same, than we can rule out an issue in the asiair at least, because I suspect the problem is in camera control with or without the asiair at the moment.
Thank you is just the minimum i can say to you for so such marvellous and interesting investigation...
Some time ago, i didn't have this problem, even though all my equipment was the same. So i'm wondering if the last asiair firmware could be the problem itself...
So i can upload files taken with previous firmware asiair version and you can have a look...
Or do you want me to take other files with Sharpcap?
Thank you is just the minimum i can say to you for so such marvellous and interesting investigation...
Some time ago, i didn't have this problem, even though all my equipment was the same. So i'm wondering if the last asiair firmware could be the problem itself...
So i can upload files taken with previous firmware asiair version and you can have a look...
Or do you want me to take other files with Sharpcap?
I am afraid that your data is just not correct in terms of sensor gain and offset value.
Your lights have gain 1 with offset 50, shot with SII filter:
HDU1 - FILTER = 'SII ' / Filter used to take image
...
HDU1 - SITELONG= '+00 00 06.310' / The site Longitude HDU1 - GAIN = 1 / The gain set (if supported) HDU1 - OFFSET = 50 / The offset/black level set (if supported) HDU1 - BAYERPAT= 'RGGB ' /
Your flats have gain 1 with offset 25 and the flats don't indicate that they were shot with the SII filter, were they?:
HDU1 - SITELONG= '+00 00 06.310' / The site Longitude HDU1 - GAIN = 1 / The gain set (if supported) HDU1 - OFFSET = 25 / The offset/black level set (if supported) HDU1 - BAYERPAT= 'RGGB '
Now the darks were shot with gain 100 and offset 25
HDU1 - SITELONG= '+00 00 06.310' / The site Longitude HDU1 - GAIN = 100 / The gain set (if supported) HDU1 - OFFSET = 25 / The offset/black level set (if supported) HDU1 - BAYERPAT= 'RGGB '
The darkflats were shot with gain 100 and offset 25
HDU1 - SITELONG= '+00 00 06.310' / The site Longitude HDU1 - GAIN = 100 / The gain set (if supported) HDU1 - OFFSET = 25 / The offset/black level set (if supported) HDU1 - BAYERPAT= 'RGGB '
So I am not that surprised that you needed an extra pedestal to get things to work more or less okay.
You supplied incompatible calibration data for both your light frames and your flat frames.
For your lights, you should have shot darks with gain 1 and offset 50, were you supplied gain 100 and ofset 25, so both sensor characteristics were not compatible with your lights. The offset difference surely creates the biggest problem 😉
Your flats needed dark flats with gain 1 and offset 25, werre you supplied darkflats with gain 100 and offset 25. In this case, the gain was not compatible.
Please make some darks and darkflats with my suggestions and try to re-calibrate your lights and flats. Make sure that the sensor temperature is the same as the lights and flats as well. Then I would think it will work properly 😉
Mabula
This post was modified 3 years ago by Mabula-Admin
@mabula-admin yho Mabula, I used 2 cameras with APT for the first time together I am sure stuff got mixed up. Would be glad if it did. I will check soon on this.
Please provide previous data (with older firmware) which worked okay 😉 That will surely help.
And please also shoot some dark flats and darks with sharpcap, that will help as well. We will be able to exclude possible root causes then .
Thanks,
Mabula
Please provide previous data (with older firmware) which worked okay 😉 That will surely help.
Here you can find some flats and lights from 2 different sessions with absolutely no problem at all (and i'm sure asiair had the previous firmware): final stacked and calibrated image was perfect as you can see here from a screenshot (except for light pollution...). The only difference with these days, was the presence of the Starizona Apex 0.65X reducer...
I haven't neither dark-flats nor darks because as soon as i complete an image included the post production too, i usually delete each calibration files and i keep only the master ones.
I checked my darks taken with an ASI533 and they had a similar histogram (image on left, below). I remembered reading about issues with USB 3 cables, particularly ZWO ones. I just replaced the original cable (which is 2m long and I used coiled up - not a good idea!) with a new, shorter one and the histogram looks a lot better (image on right).
Hello, I have really wide stripes in my pictures. The USB cable of the camera (original ZWO) caught the WiFi signal from the imaging PC. I replaced it with a better shielded USB cable. Then the thick bars disappeared. Then I taped off all the light leaks (filter drawer, ventilation openings on the telescope and transition between dew cap and telescope). Then all the calibration problems disappeared.
found some time to further check: redid the files with offset and gain the same. fist sezzion looks good, see below. just lightpollution. second sezzion, same calibration data, has a black hole. retried even without masters, result looks the same.
do you have an idea what this is? the file data looks the same, means same gain, offset, temp ... of course noting ales was changed, like filters (l-extreme). flats were done with a dimmed flatfield box, exposure 0.9 s.
one thing I understand is that the flats to these cameras seem to be very sensitive to paramter settings.
I guess something must differ, which I do not see ...
Please provide previous data (with older firmware) which worked okay 😉 That will surely help.
Here you can find some flats and lights from 2 different sessions with absolutely no problem at all (and i'm sure asiair had the previous firmware): final stacked and calibrated image was perfect as you can see here from a screenshot (except for light pollution...). The only difference with these days, was the presence of the Starizona Apex 0.65X reducer...
I haven't neither dark-flats nor darks because as soon as i complete an image included the post production too, i usually delete each calibration files and i keep only the master ones.
I am also seeing some variance in Flats with my ASI6200MM Pro and Baader LRGB CMOS Optimised filters, and Ultrafast Certified Narroband (3.5nm and 4nm) on my F2.8 Sharpstar.
With an ADU of 32000 I get undercorrection with the Narrowband, I have found that an ADU of around 22500 gives me better results, these are all at Gain 100
I am really struggling with my LRGB flats though, they are not being entirely corrected and I have tried 22500, 25000, 32000 and 50000, 50000 was far worse.
My flats have been calibrated against BIAS, I am going to try this with flat darks too and see what comes out the other side.
