QHY268 question (or other IMX571 camera like ZWO ASI2600)

[inFINNity Deck]

Dear Stargazers,

I was offered an occasion QHY268M that has barely been used. Before acquiring it I asked for some darks, which I took together with the owner, but those raise some questions. If I zoom in I see that some 1% of the pixels have an ADU of about 24800 on a background level that is only 1% of that (i.e. around 250-300), which seems a bit high to me:

 

I have placed three FITS-files on my server:

https://www.dehilster.info/astronomy/docs/TestShot__0.50s_-15.0C.fit
https://www.dehilster.info/astronomy/docs/TestShot_-0.05s_-5.0C_avg16kADU.fit
https://www.dehilster.info/astronomy/docs/TestShot_-0.05s_-5.0C_avg33kADU.fit

The first is a dark at -15°C at 0.5s exposure time, the second and third are at -5°C and were allowed to collect some photons at 0.05 seconds each, resulting in an average ADU of about 16k and 33k. They were all taken without telescope attached.

I would like to know whether this is typical for the IMX571 or QHY268M or is it perhaps due to the short exposure times?

I would appreciate if there any IMX571 users on this forum that are willing to share some darks and/or lights with me.

thanks in advance for your input!

Nicolàs

[Clarkey]

I don't have a mono IMX571, but my darks look nothing like yours. The histogram looks very odd too. Personally, I would say there is clearly something wrong with the camera.

[Gary Clayton]

Seem very short for dark frames, that being said they do look very odd and nothing like my 300 second darks from my IMX571 camera.

[inFINNity Deck]

8 minutes ago, Gary Clayton said:

Seem very short for dark frames, that being said they do look very odd and nothing like my 300 second darks from my IMX571 camera.

Hi Gary,

thanks for your reply. Could you do me a favour and create a dark using this same short exposure time, so that we can see that the exposure time causes it? We made the dark at daytime, so decided on a short exposure time to avoid light issues, but perhaps it was shorter than what the camera can handle (although I do take darks of milliseconds on my ZWO planetary cameras without issue to remove hot pixels).

Nicolàs

 

[Gary Clayton]

Will do, just give me a day or two.

[teoria_del_big_bang]

I agree something looks very odd with that dark.
Shortest dark I have with my QHY268M  is 4S and unfortunately cannot try to take any at the moment but the difference is chalk and cheese. These two images are stretched  exactly the same, the left is yours and the right my 4 second one.

What gain and offsets were you using, there seems to be very little info in the fits header ?
I take it this is a single dark not a stacked one ?

It doesn't look like light leak either when taking the image.

I do have a 0.3S Bias, so basically similar to your 0.5S dark and again at same stretch as above looks nothing like yours.

Steve

Edited October 27, 2023 by teoria_del_big_bang

[inFINNity Deck]

Hi Steve,

thanks for your reply and images.

22 minutes ago, teoria_del_big_bang said:

What gain and offsets were you using, there seems to be very little info in the fits header ?

The header is indeed pretty poor. The -15°C image was taken at Gain 26 and Offset 16 in Readmode extended FullWell 2CMS. The other images in the mode Photographic DSO at Gain 56 and Offset 32.

22 minutes ago, teoria_del_big_bang said:

I take it this is a single dark not a stacked one ?

That is correct.

22 minutes ago, teoria_del_big_bang said:

I do have a 0.3S Bias, so basically similar to your 0.5S dark and again at same stretch as above looks nothing like yours.

That indeed looks much better...

Nicolàs

[teoria_del_big_bang]

Hi Nicolàs,

Mine are using Gain56, offset 25 and mode #1 (High Gain Mode) , I do not think in my firmware I actually have the CMS modes I seem to remember only 4 modes when I set mine up and not looked into updating the firmware, whether that would make a difference I do not know but I would be surprised as it is intended to extend the fullwell so don't see why you would get this effect.
But can you try the same mode as my frames just to check ?

Steve

[inFINNity Deck]

38 minutes ago, teoria_del_big_bang said:

Hi Nicolàs,

Mine are using Gain56, offset 25 and mode #1 (High Gain Mode) , I do not think in my firmware I actually have the CMS modes I seem to remember only 4 modes when I set mine up and not looked into updating the firmware, whether that would make a difference I do not know but I would be surprised as it is intended to extend the fullwell so don't see why you would get this effect.
But can you try the same mode as my frames just to check ?

Steve

Hi Steve,

thanks for that info. I have passed it on to the owner and asked him to take an image in that way.

Nicolàs

[ONIKKINEN]

Apparently the 571 sensor has a large number of hot pixels - at least in comparison to some other sensor models. There was a mention or two regarding this in a thread here:

Dont have the QHY version, but the RisingCam OSC version of the 571. Just tested my 240s x 50 dark stack and with 2 sigma i have more than 34k hot pixels some of which fully saturated. Looks like mine is not too different from yours in that sense.

Edited October 27, 2023 by ONIKKINEN

[tomato]

Sorry for the late response, here is my Master Dark and BPM data from my QHY268M, -10 deg C, 120 secs, 30 frames for the MD. I have no idea if these numbers are good, bad or indifferent, but I have attached the image using the camera and it seemed to calibrate OK.

BPM

Master Dark

[Stuart1971]

23 hours ago, inFINNity Deck said:

Dear Stargazers,

I was offered an occasion QHY268M that has barely been used. Before acquiring it I asked for some darks, which I took together with the owner, but those raise some questions. If I zoom in I see that some 1% of the pixels have an ADU of about 24800 on a background level that is only 1% of that (i.e. around 250-300), which seems a bit high to me:

 

I have placed three FITS-files on my server:

https://www.dehilster.info/astronomy/docs/TestShot__0.50s_-15.0C.fit
https://www.dehilster.info/astronomy/docs/TestShot_-0.05s_-5.0C_avg16kADU.fit
https://www.dehilster.info/astronomy/docs/TestShot_-0.05s_-5.0C_avg33kADU.fit

The first is a dark at -15°C at 0.5s exposure time, the second and third are at -5°C and were allowed to collect some photons at 0.05 seconds each, resulting in an average ADU of about 16k and 33k. They were all taken without telescope attached.

I would like to know whether this is typical for the IMX571 or QHY268M or is it perhaps due to the short exposure times?

I would appreciate if there any IMX571 users on this forum that are willing to share some darks and/or lights with me.

thanks in advance for your input!

Nicolàs

They are not darks at that short exposure, they are bias frames….and look perefectly normal, unless of course you blow them up to the sizeyou have…

Dark Frames should be the same length as the light exposures you are going to use, 0.5 is not a dark at all but a bias frame…

You are worrying over nothing here…

Edited October 28, 2023 by Stuart1971

[Stuart1971]

19 hours ago, teoria_del_big_bang said:

I agree something looks very odd with that dark.
Shortest dark I have with my QHY268M  is 4S and unfortunately cannot try to take any at the moment but the difference is chalk and cheese. These two images are stretched  exactly the same, the left is yours and the right my 4 second one.

What gain and offsets were you using, there seems to be very little info in the fits header ?
I take it this is a single dark not a stacked one ?

It doesn't look like light leak either when taking the image.

I do have a 0.3S Bias, so basically similar to your 0.5S dark and again at same stretch as above looks nothing like yours.

Steve

Those are not darks he has posted but bias frames, and if blown up to the point of the pixels looking square then all out frames would look like that…yours look the same as mine…

[teoria_del_big_bang]

1 hour ago, Stuart1971 said:

Those are not darks he has posted but bias frames, and if blown up to the point of the pixels looking square then all out frames would look like that…yours look the same as mine…

I agree that they it is essentially a bias frame but I am not sure it looks same as my 0.3 sec .
The frame size is same as mine but if I magnify both images to same size the 0.5 test shot of the OP seems to have a lot of hot pixels that my 0.3 bias does not.

  

Mine on left I am struggling to find any pixels above 0.01 whereas the OP's has a lot at 0.3791.
Am I doing something wrong here both are unstretched just a temporary stretch in PI to see the pixels easier, which does not affect the readout of pixel values, both are blown up same size.

Apart from all these "hot pixels which all seem to be almost an identical values between 0.3790 and 0.3792 which is a bit all they are all almost exactly the same, then all other pixels are about same readout as mine.

Now again as it stands I have no images at this extended fullwell mode used on his image, so both images are taken on different modes, whether this has an affect I am not sure, I wouldn't think it would.

And again when viewed as normal these hot pixels may not have any effect, I am not saying they do and with processing should be taken out.
So you are probably correct that this is normal but just a bit different to mine, for whatever reason.

 

And looking at the statistics they are significantly different, but again I admit I do not know what difference this makes to a final image, maybe nothing, and also because they are normalised but taken in different modes then maybe not a like for like comparison, below is the 16 bit values.

So it does show a difference but apart from minimum and maximum values the mean looks comparable with my 0.3 sec image being 405 and the longer 0.5 exposure is 765 which due to different exposure lengths is comparable.

Now because I am no expert I am not sure what all this means but I would imaging after processing the extra hot pixels will not have any effect as they will be removed with the processing.

@Stuart1971 does any of my rabble make sense ?

Steve

 

Edited October 28, 2023 by teoria_del_big_bang

[Stuart1971]

1 hour ago, teoria_del_big_bang said:

I agree that they it is essentially a bias frame but I am not sure it looks same as my 0.3 sec .
The frame size is same as mine but if I magnify both images to same size the 0.5 test shot of the OP seems to have a lot of hot pixels that my 0.3 bias does not.

  

Mine on left I am struggling to find any pixels above 0.01 whereas the OP's has a lot at 0.3791.
Am I doing something wrong here both are unstretched just a temporary stretch in PI to see the pixels easier, which does not affect the readout of pixel values, both are blown up same size.

Apart from all these "hot pixels which all seem to be almost an identical values between 0.3790 and 0.3792 which is a bit all they are all almost exactly the same, then all other pixels are about same readout as mine.

Now again as it stands I have no images at this extended fullwell mode used on his image, so both images are taken on different modes, whether this has an affect I am not sure, I wouldn't think it would.

And again when viewed as normal these hot pixels may not have any effect, I am not saying they do and with processing should be taken out.
So you are probably correct that this is normal but just a bit different to mine, for whatever reason.

 

And looking at the statistics they are significantly different, but again I admit I do not know what difference this makes to a final image, maybe nothing, and also because they are normalised but taken in different modes then maybe not a like for like comparison, below is the 16 bit values.

So it does show a difference but apart from minimum and maximum values the mean looks comparable with my 0.3 sec image being 405 and the longer 0.5 exposure is 765 which due to different exposure lengths is comparable.

Now because I am no expert I am not sure what all this means but I would imaging after processing the extra hot pixels will not have any effect as they will be removed with the processing.

@Stuart1971 does any of my rabble make sense ?

Steve

 

Yea it does, and I agree with you, he does seem to have a lot more hot pixels, I assume you both had same temps on the frames…? As that is what will make the difference…

Edited October 28, 2023 by Stuart1971

[teoria_del_big_bang]

1 hour ago, Stuart1971 said:

Yea it does, and I agree with you, he does seem to have a lot more hot pixels, I assume you both had same temps on the frames…? As that is what will make the difference…

I think mine was -10 and the OP's -15

Steve

[Stuart1971]

2 hours ago, teoria_del_big_bang said:

I think mine was -10 and the OP's -15

Steve

Ok, so in theory his should have been better, maybe his cooler is not working….🤔

Edited October 28, 2023 by Stuart1971

[teoria_del_big_bang]

31 minutes ago, Stuart1971 said:

Ok, so in theory his should have been better, maybe his cooler is not working….🤔

The setpoint according to the header was -20 but actual was -15. Which funnily enough is about as low as mine will go, I struggled to get it past -15 unless a very cold night, and as the camera has a very low readout noise anyway I always used -10 so cooler doesn't need to struggle.

Steve

[Stuart1971]

1 hour ago, teoria_del_big_bang said:

The setpoint according to the header was -20 but actual was -15. Which funnily enough is about as low as mine will go, I struggled to get it past -15 unless a very cold night, and as the camera has a very low readout noise anyway I always used -10 so cooler doesn't need to struggle.

Steve

Yes me too, always -10..👍🏻

[inFINNity Deck]

Thanks guys for your input, much appreciated! I just came back home and found a few new files captured in different ways with the camera I was offered. Will analyse them tomorrow and post the results here. What I can say, is that those high pixels are not hot pixels as they appear randomly in the images, so it seems to be more a kind of shot noise (random telegraph noise), but with strange high values.

Maybe it is also good to explain why I am concerned: I plan to use the camera for spectroscopy with a 2400lpm grating (R around 17000). At this moment I am using a LHires III with a QHY163 mono, which is only 12bit. At this high resolving power the data of 600s capture of a mag 5.4 star only is 50% higher in ADU than the background (approximately 3200 ADU signal vs 2000 ADU background). Using these relative short exposure times we (an international group of 12 observers) are trying to find short period variability in Be-stars. So stacking is no option, while the low photon levels makes it difficult (if not pointless) to do multiple captures and stack them.

The QHY163 does not show the same kind of noise in the images I get from this QHY268, nor is that the case for the two ZWO ASI1600MM Pro Cool cameras I use (same sensor as the QHY163), nor with the ZWO ASI174MM, ASI290MM and ASI290MC I use.

Here are three histograms for comparison (all of darks, histograms by APP):

Nicolàs

 

[Stuart1971]

28 minutes ago, inFINNity Deck said:

Thanks guys for your input, much appreciated! I just came back home and found a few new files captured in different ways with the camera I was offered. Will analyse them tomorrow and post the results here. What I can say, is that those high pixels are not hot pixels as they appear randomly in the images, so it seems to be more a kind of shot noise (random telegraph noise), but with strange high values.

Maybe it is also good to explain why I am concerned: I plan to use the camera for spectroscopy with a 2400lpm grating (R around 17000). At this moment I am using a LHires III with a QHY163 mono, which is only 12bit. At this high resolving power the data of 600s capture of a mag 5.4 star only is 50% higher in ADU than the background (approximately 3200 ADU signal vs 2000 ADU background). Using these relative short exposure times we (an international group of 12 observers) are trying to find short period variability in Be-stars. So stacking is no option, while the low photon levels makes it difficult (if not pointless) to do multiple captures and stack them.

The QHY163 does not show the same kind of noise in the images I get from this QHY268, nor is that the case for the two ZWO ASI1600MM Pro Cool cameras I use (same sensor as the QHY163), nor with the ZWO ASI174MM, ASI290MM and ASI290MC I use.

Here are three histograms for comparison (all of darks, histograms by APP):

Nicolàs

 

Hot pixels are random….

[inFINNity Deck]

Yesterday I received three bias-frames and oddly enough there was a big difference between them (histograms by APP, pasted in the screen-dump of AvisFV):

It appears that Voyager, the software used to capture the images, has a low quality mode at which the FITS can be stored. The owner switched to another mode which made the FITS looking much better. Later this week I hope to receive a few dark frames using a different setting in Voyager.

Nicolàs

[Oddsocks]

On 27/10/2023 at 12:54, inFINNity Deck said:

Dear Stargazers,

I was offered an occasion QHY268M that has barely been used. Before acquiring it I asked for some darks, which I took together with the owner, but those raise some questions. If I zoom in I see that some 1% of the pixels have an ADU of about 24800 on a background level that is only 1% of that (i.e. around 250-300), which seems a bit high to me:

I would like to know whether this is typical for the IMX571 or QHY268M or is it perhaps due to the short exposure times?

I would appreciate if there any IMX571 users on this forum that are willing to share some darks and/or lights with me.

thanks in advance for your input!

Nicolàs

Hi Nicolàs.

Here are five sample 0.5s darks from a QHY268M all at -15c.

https://www.dropbox.com/scl/fo/ju1ai9wtjm0ljwmr8za2n/h?rlkey=shytpkndpaluyqik6rq9ztgyy&dl=0

These are nothing like your test images, the hot pixels in your images being mostly a uniform ~24,844 ADU is not normal, and this is not replicated in the images from my own camera.

The file headers in my samples have all the information you need for comparison and the images were captured with MaxIm DL v6.40 with only the FITS headers being sanitised for personal identifiable information in PixInsight before saving and uploading to DropBox

As I only have the 2GB basic DropBox allowance I'll only host these for seven days before deleting, I don't have the storage space to keep them longer.

The five frames were taken with the following settings:

0.5s, Dark, (Covered OTA wrapped with darkroom blind material and closed Flip-Flat), ExFullWell_2CMS curve, Gain:26, Offset:16, -15c, Fast Readout mode.

0.5s, Dark, (Covered OTA wrapped with darkroom blind material and closed Flip-Flat), ExFullWell_2CMS curve, Gain:26, Offset:16, -15c, Normal Readout mode.

0.5s, Dark, (Covered OTA wrapped with darkroom blind material and closed Flip-Flat), ExFullWell curve, Gain:26, Offset:16, -15c, Fast Readout mode.

0.5s, Dark, (Covered OTA wrapped with darkroom blind material and closed Flip-Flat), ExFullWell curve, Gain:26, Offset:16, -15c, Normal Readout mode.

And a comparison file with the settings I normally use:

0.5s, Dark, (Covered OTA wrapped with darkroom blind material and closed Flip-Flat), PhotoDSO_2CMS-0 curve, Gain:26, Offset:10, -15c, Normal Readout mode.

Before condemning the camera try acquisition with a different capture program, just on the off-chance that the capture program you used to test the camera has not correctly set the requested capture curve and gain/offset values, also be sure that the QHY Drivers/capture software is up-to-date.

HTH

William.

[inFINNity Deck]

Dear William,

thanks a lot for these five images, what a difference these make! A quick inspection learned that there are not even a handful pixels that have ADU above 1000 (one thousand). I would be happy all day with that! 🙂

As I wrote in my previous post there indeed seems to be an issue with Voyager, at least in Low Quality mode. So the owner will try to produce subs in High Quality mode, but I also asked him to create a few subs with the QHYCCD software, that (I hope) should at least produce raw data. I will forward your post to him and ask him to replicate.

Nicolàs

 

[inFINNity Deck]

Here are the histograms of William's subs:

Nicolàs