Some of you may remember my M16 Eagle Nebula posted on Aug 09, 2018
(http://gallery.orpington-astronomy.org.uk/albums/userpics/10050/thumb_light_BINNING_1_integration_ABE_MLT_ARCSINH_TGVD_HDRMT_MT_CS_HT.jpg) (http://forum.orpington-astronomy.org.uk/index.php?topic=11429.0).
It had strange colour blotches on it, very technicolour but definitely not an accurate representation of the target! There has been a discussion about this on Cloudy Nights https://www.cloudynights.com/topic/636301-asi294mc-calibration-%E2%80%93-testing-notes-thoughts-and-opinions/ (https://www.cloudynights.com/topic/636301-asi294mc-calibration-%E2%80%93-testing-notes-thoughts-and-opinions/) and it sems to be a 'feature' off BSI (Back Side Illuminated) sensors. I have been battling with a second frame to the IC1805 Heart Nebula I posted recently, it has this problem in spades and I can't see a way round it. The other odd thing is if I stack all my 164 good subs (over 5 hours) I get a worse result than if I only stack the very best 80 subs. This image has been dark subtracted (only) which as per the article does seem to make matters worse.
I think the way CMOS camera subs are collected and processed is going to have to be different to the traditional CCD/DSLR processing as a result. I've spent hours trying to get the subs to stack and process in PixInsight to no avail. My best results are coming from DeepSkyStacker using no calibration frames or any other settings that affect the result (apart from Bilinear debayering) and loading the standard stacked Autosave file into StarTools which actually prefers to deal with uncalibrated stacks.
(http://gallery.orpington-astronomy.org.uk/albums/userpics/10050/normal_CMOS_Blotch_Problem.jpg) (http://gallery.orpington-astronomy.org.uk/albums/userpics/10050/CMOS_Blotch_Problem.jpg)
Same but re-stacked without the dark. Processing in Star Tools was Linear Bayered not whitebalanced, Crop 75px, Wipe Default Temp AutoDev, screen dump to JPG, same for both pictures. Now there's a different blotch!
(http://gallery.orpington-astronomy.org.uk/albums/userpics/10050/normal_CMOS_Blotch_Problem_NoDark.jpg) (http://gallery.orpington-astronomy.org.uk/albums/userpics/10050/CMOS_Blotch_Problem_NoDark.jpg)
Much better Duncan,
Roger
Very odd Duncan.
Is there any chance you could upload your stacked file/s (perhaps the best 80 and then separately the 164 subs stacked. So we can have a "go" at them. Perhaps you could also upload the best 80 with flats, darks and bias applied too.
I must say - although many people think it is wrong, I get better results often without using bias at all which seems to completely mess up the images, but not every time.
Can you upload to something like Dropbox as a Tiff file (i.e. not the pixinsight file name).
I'll meanwhile have a read of that link.
Carole
Hi Carole,
That could be useful, they are Fits files from DSS. I'll let you know where they can be downloaded from later, I'll do various combinations.
Duncan
I look forward to having a "go". I did try to do something with your first image but there were different coloured blotches all over it.
I came unstuck with my OSC camera and I think it was the debayering. I was fine all the time I used APT, but then APT stopped working and I tried using Nebulosity, I stacked using the correct debayering for the camera but you should see the results I got with that, I might post it up if I can find it. In the end I decided it was too much faff and mono was easier so I got rid of it.
Carole
PS: Found it - you can just about make out the target I was imaging. This was back in December 2014.
At the time I had cleaned the sensor and thought I had got alcohol behind the sensor, but eventually someone tested it for me who had experience with this camera, and it was fine, so I sold it. It was Robin of Sharpcap who finally diagnosed that the stacked software had got confused with the debayering, despite me using the recommended format.
(https://cdn.astrobin.com/thumbs/3EGVxsPZffBV_620x0_wmhqkGbg.jpg)
I now remember doing some analysis on that sensor:
https://www.cloudynights.com/topic/596025-zwo-asi294-mc-pro/?p=8631836
The problem is that the pins on the rear of the sensor mean that the cooling is not in direct contact with the chip. As a result the sensor can never be cooled evenly and the dark current varies across the sensor.
It's a great sensor for real time astronomy but unfortunately not so suitable for long exposure deep sky work.
If it's any consolation, I never managed to resolve the purple/green swathes problem on my Sony A7S. I have to resort to sophisticated background subtraction.
https://www.cloudynights.com/topic/576265-sony-a7s-purplegreen-swathes/
Mark
I had a VERY vivid dream about this last night, (no accounting for dreams) and my conclusion in the dream was that darks should take away this colour noise, in the dream I first thought it needed flat darks, but no accounting for dreams lol.
But just to say this must very very disappointing after purchasing what should have been an improvement to DSLR imaging just to find you have acquired a new set of problems. Some people seem to be having some good success with CMOS imaging, but others having lots of problems.
Is the pattern consistent in all images you do, if so maybe you could make some sort of extraction image, but not quite sure where you would need to apply it as yet.
What do stretched flats and stretched darks look like?
Carole
Hi Carole, what a thing to dream about!
I think the answer is not to calibrate but to use software to correct vignetting and noise. The sub's I get are very low noise and I've worked out if the main mirror is at the back end of its movement I get very little vignetting. Dust bunnies have never been a problem for my setups.
The other thing is to abandon the idea if lots of short sub's. More signal per low noise sub is going to swamp the blotches. One thing in the article is to alternate long and short sub's in he shooting plan, I tried this last night with M42 and have stacked 120s with 30s and 10s subs using entropy weighted (for HDR) in DSS and it looks good. Need to get the result into StarTools later after my two hour French lesson.
Did you take a look at the master dark and master flat to see if either of these contain the colour blotches?
Lol, yes my dream consisted of you standing up at an OAS meeting and doing a presentation on it.
Any chance of those download links yet?
Carole
The smarty pants on CloudyNights (not Mark for a change!) has been through all the options. The chips don't produce consistent patterns. They were designed for low light video applications. Its a great planetary camera! Mark found similar issues with his Sony A7s.
I have never used Bias but always do Flat Darks, as you should if not using Bias
QuoteThe chips don't produce consistent patterns. They were designed for low light video applications.
Yet they sold it as a Deep Sky imaging camera?
I think I'd be asking for my money back or an exchange of camera.
Carole
Quote from: The Thing
The smarty pants on CloudyNights (not Mark for a change!) has been through all the options. The chips don't produce consistent patterns. They were designed for low light video applications. Its a great planetary camera! Mark found similar issues with his Sony A7s.
I'm dead impressed by the effort he has put into his analysis. Maybe if I tried a bit harder I would make a bit more progress in understanding my Sony A7S! For one reason or another there do appear to be calibration issues and colour gradients on many Sony CMOS sensors.
Mark
Fascinating article, but I felt his position on dark frames wasn't consistent.
It starts by saying dark current is non-linear with temp and time, but concludes that it's OK to use scaled dark frames(?). The implication of his first bit of work was library darks would not work. Pretty conclusive on bias frames though. Apart from the serious Amp glow issues, it sheds no light on the blotching, but suggests that problems may occur through flats (if taken using exposures sub 3 seconds - which all of mine are). The suggestion that the response will vary dependent on what the chip is or has been doing is also quite worrying (and could account for blotches - but not I suspect your original ones). I was quite interested in this camera, but am starting to go off the idea... Did you look at the dark frames for blotching?
Can you get round the problem?
The way round it I'm using is not to use any calibration at all. I'm tweaking my scope to give an evenly illuminated field as its supposed to provide one. I'm consequently getting better results. I've tried a long/short alternate exposure plan and that seems to do the trick. I've done a new sigma stack of Orion using these and the 120s sub's I used before and the result is very much better.
I'm gutted that you're having all this trouble Duncan. Do you think you'll be able to get over this issue ?
Robert
Well, yes. As mentioned, since calibration causes the issue, ditch the calibration.
Quoteditch the calibration.
How do you compensate for lack of flats re vignetting and dust bunnies?
Carole
Hi Carole,
Never had a dust bunny visible on a stacked image and I've think I've got my Telescope Service scope sorted so there is minimal vignetting. In StarTools the best starting point is an uncalibrated stack. There are very good tools for correcting vignetting and noise. I've spent days trying to get the same sort of results in PixInsight to no avail.
Duncan
Just been reading Marks post about diffraction patterns and microlenses.
At least with the colour blotches there are things to try. I have images where they didn't manifest at all so it must be solvable. The next thing I'll try is a stable DC power supply with low/no ripple for the USB3 hub (which powers the camera) and separately for the cooling which currently varies the chip temp by more than 0.5c once its 'reached' temperature. At the moment they are both fed via 'direct' takeouts on the Kendrick dew heater controller, so that switching may be affecting things as well. Voltage instability may be a function of living out in the sticks and/or having an electric water heater for the underfloor heating (off most of the night) and another for hot water heater (on all night for cheap rate juice). I'll keep experimenting.
Also I have had trouble collimating for a while so I went back to first principles. The focuser (held by two tiny grub screws) wasn't in straight! I also re-adjusted the crayford tensions and that noticeably straightened the focuser tube! Collimating with the Concenter tool was a doddle and things finally 'looked' right. If it's now right I will have a lot more signal arriving on the CMOS and this should swamp the blotch causing whatever in the CMOS. Where are those pesky stars when you need em!
Hi All,
This may come in useful to someone...
I have replaced shared power supplies (12V laptop variety) with individual ones for each power need. This affects the 'industrial' USB3 hub which powers the cameras and the TEC cooling on the ASI294MC Pro. This seems to have completely solved the blotch problem. I suspect power output ripple and variation caused by items changing their power needs is a factor. I need to do some PI processing and stretching to verify this as I have been using StarTools recently due to PI display issues.
I also now think ambient temperature affects the efficacy and stability of the TEC cooling to a great degree. I might try making an insulating jacket for the camera body so that in warm weather it's not fighting the cooling by absorbing heat from the environment. In cold weather this shouldn't be needed. With an ambient temperature of 5C the TEC only drew 50% power to keep the CMOS at -20C, at 15C it was 100%. The CMOS temperature also flips up and down 0.5C every few seconds, this might be a measurement error or the effect of the solder blobs connecting the sensor to its backplane not being effective conductors.
I have also upped the ADU count for my flats, I was using 20000 which is the default in the APT Flats Aid tool, I have increased it to 32000ADU which is about 1/2 full well depth on this camera and suddenly the flats are correcting properly again!
All good stuff.
Duncan
Quote from: The Thing on Dec 18, 2018, 10:34:59
I might try making an insulating jacket for the camera body so that in warm weather it's not fighting the cooling by absorbing heat from the environment. In cold weather this shouldn't be needed. With an ambient temperature of 5C the TEC only drew 50% power to keep the CMOS at -20C, at 15C it was 100%. The CMOS temperature also flips up and down 0.5C every few seconds, this might be a measurement error or the effect of the solder blobs connecting the sensor to its backplane not being effective conductors.
is that just for your colour camera as i don't seem to have a blotch problem with my cmos mono and given the amount you pay for this equipment should you have to do this for efficiency as they should be made to work in hot temps as well as cold.
Roger
Glad you are getting sorted Duncan, though these cameras should be fit for the purpose they are intended in the first place, and not having to solve mysteries as to why they behave badly.
How are you managing to power 12V power separately and how many have you got?
I currently have 5 to power.
2 Mono cameras, 2 Electronic filterwheels and my dew heaters, all running off the same 12v adapter through 12V splitters. Luckily mine seems to work fine.
I don't as a rule use a USB hub though but use two separate laptops instead.
Carole
Quote from: Apophis on Dec 18, 2018, 12:02:59
is that just for your colour camera as i don't seem to have a blotch problem with my cmos mono and given the amount you pay for this equipment should you have to do this for efficiency as they should be made to work in hot temps as well as cold.
Roger
Yes. Other colour CMOS cameras seem to exhibit the same sort of artefacts but I don't think any mono CMOS users have reported the equivalent grey blothc problem.
Thanks Carole. I think it's down to the change of tech. I am sure if you went back to the dawn of CCD there would have been similar problems identified and overcome, hence the use of Darks and Bias frames and the introduction of cooling for instance.
I now have separate 12v supplies for USB3 hub (main camera, guide camera, TemperHum sensor, mount control) 4A, camera cooler 5A, mount 5A, dew heater controller which still shares with the focuser controller (6.5A) and of course laptop (which is 19v). They run through surge protected plug strips and there are ferrite rings at strategic locations - mostly as part of the power bricks' leads.
Hi Duncan,
I'm really glad you've sorted the problem out, must admit I was a bit shocked to see where you were powering the camera from. I've got a few of ultra low ripple (>1mv rms) PSU modules to go into my mk2 power brick, one will be dedicated to the camera another to the USB hub and the last to mount/dew bands and other "dirty" noise sources.
Regarding ADU levels for flats, I go for about 2/3rds full well count (40000 ADU). The main reason is that the edges, where the signal is lowest, will add more noise if the ADU values are low. If you are using 32000 peak then the lowest edge level might be just 10000 depending on vignetting - worth considering as the edge is also part of the image and needs just as much s/n ratio as the rest.
Robert
Hi Robert,
I've used a PC power supply unit for DSCs etc. for years, obviously OK for a DSLR but not a proper camera. I haven't been using that in the observatory though Have you got a particular make of power supply? I've had a look and there seem to be endless bench supplies and other units/modules/PCBs to choose from but very few give ripple figures. I've got a DC-DC converter coming which does have a resonable ripple figure quoted and I'm going to feed that from a Toshiba laptop power brick (19v) and use it for the hub and by implication, the camera.
And I'll try a higher ADU for the flats...
Hmm, I have been using between 22,000 and 30,000 ADU for flats, and generally try to aim for around 22,000 - 24,000. I find they work for me but maybe it is different for a CMOS camera.
Carole
I might try two sets on next session to see what works best
Roger
Quote from: Carole on Dec 19, 2018, 16:01:21
Hmm, I have been using between 22,000 and 30,000 ADU for flats, and generally try to aim for around 22,000 - 24,000. I find they work for me but maybe it is different for a CMOS camera.
Carole
It's nothing to do with CMOS, I did that with CCD cameras as well.
Robert