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QHY268M-PH Horizontal Banding

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#1 David Rosenthal

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Posted 22 June 2022 - 09:36 AM

I received my replacement QHY268M camera recently after having received a dead one. Of course it has been raining since so I decided to experiment with my flat panel to see what flats will look like.

Very happy to see that the 36mm filters with the Tak Reducer QE on my FSQ-106 did not really vignette at all. Just a tiny amount.

I did notice some strange banding, in all DL modes, which is more noticiable as exposure time is decreased.

I can see it in 3.5 second L flats.

Has anyone else seen this and is this something I should be worried about.

Here are some files to look at.

https://pbase.com/djrlx90/qhy268m

I’d appreciate any information you have while I’m still inside my 30 day return window.


Sent from my iPhone using Tapatalk

Edited by David Rosenthal, 22 June 2022 - 09:37 AM.


#2 SilverLitz

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Posted 22 June 2022 - 12:19 PM

I have not noticed any banding with my QHY268M, which I have had since Spring 2021.

 

My challenge with the 268, which I love (and bought the 268C as well, but have not yet used), is moving dust spots between flat and light acquisition.   This is generally only a single spot, out of many, on the sensor cover glass.  I speculate that 16-bit sensors have many more problems with dust spots shifting on the sensor compared to 12-bit sensors when nothing is changed due to the noise floor being 16x lower making them visible.  Since day one, I have noticed many more spots on the 268 that would be near the sensor that those in 2 year use of my 183; again I suspect much lower noise floor being the cause, e.g. similar spots are their in the 183, but buried by the noise floor. 

 

Small changes on the 268 are noticeable than would be buried in the noise floor with my 12-bit ASI183mm-Pro (used for 2yr prior to the 268, with few flat issues).  I have made after the fact flat spot repairs (or changes to a residual spot on master light) using PixelMath that are sensitive to ~0.000010 differences, which is close a 16-bit step of 0.000015 (1/ 2^16), supportive of my quantization noise floor cause.  By comparison 12-bit step is a much larger 0.000244, of which a 0.000010 difference would not show up.


Edited by SilverLitz, 22 June 2022 - 12:23 PM.


#3 jkcolli

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Posted 22 June 2022 - 08:57 PM

Please go to this url

https://www.qhyccd.com/qhy600m-c/

 

Scroll down to the section:   Minimize Horizontal Banding

 

Jack


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#4 bhalkett

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Posted 22 June 2022 - 09:18 PM

I have not noticed any banding with my QHY268M, which I have had since Spring 2021.

 

My challenge with the 268, which I love (and bought the 268C as well, but have not yet used), is moving dust spots between flat and light acquisition.   This is generally only a single spot, out of many, on the sensor cover glass.  I speculate that 16-bit sensors have many more problems with dust spots shifting on the sensor compared to 12-bit sensors when nothing is changed due to the noise floor being 16x lower making them visible.  Since day one, I have noticed many more spots on the 268 that would be near the sensor that those in 2 year use of my 183; again I suspect much lower noise floor being the cause, e.g. similar spots are their in the 183, but buried by the noise floor. 

 

Small changes on the 268 are noticeable than would be buried in the noise floor with my 12-bit ASI183mm-Pro (used for 2yr prior to the 268, with few flat issues).  I have made after the fact flat spot repairs (or changes to a residual spot on master light) using PixelMath that are sensitive to ~0.000010 differences, which is close a 16-bit step of 0.000015 (1/ 2^16), supportive of my quantization noise floor cause.  By comparison 12-bit step is a much larger 0.000244, of which a 0.000010 difference would not show up.

Ditto on the dust.  Anytime the sensor window is exposed I expect to get a bunch of dust. I never experienced anything remotely like that with my ASI533.



#5 David Rosenthal

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Posted 22 June 2022 - 09:57 PM

Please go to this url
https://www.qhyccd.com/qhy600m-c/

Scroll down to the section: Minimize Horizontal Banding

Jack

I tried many different values of the USB Traffic parameter and did not see any difference. I am using it through a powered USB2 hub.

#6 SebaAstro

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Posted 23 June 2022 - 01:46 PM

Do you have the banding only when taking Flats? DO you take the flats with flat panel or natural light?

 

I have the QHY268M and never had that issue but I experienced those bendings before with a ZWO camera. Actually i found out that the problem wasn't the camera but using a battery to power my LED flat panel. Using a different power supply to power my LED flat panel eliminated the issue (again the issue was not in the camera :)). It had to do with some sort of frequency interference between the two systems. 

 

Seba



#7 David Rosenthal

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Posted 23 June 2022 - 02:10 PM

Do you have the banding only when taking Flats? DO you take the flats with flat panel or natural light?

I have the QHY268M and never had that issue but I experienced those bendings before with a ZWO camera. Actually i found out that the problem wasn't the camera but using a battery to power my LED flat panel. Using a different power supply to power my LED flat panel eliminated the issue (again the issue was not in the camera :)). It had to do with some sort of frequency interference between the two systems.

Seba


I have only taken bias and flat frames. I use a dimmable light panel that I have had for over 10 years and have never caused any issues with.

I power it with the same Pyramid 12VDC power supply that I power the usb2 hubs and the camera. It could very well be interference. I will try using the supply that came with the camera and see if that changes anything.

Thanks for this idea.

#8 pfile

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Posted 23 June 2022 - 10:47 PM

i just went thru something similar though with an ASI camera. bottom line is that the banding may look bad but actually be fine; you should try measuring the read noise of the sensor and see if it is within spec. in my case the read noise of the camera was a little better than spec, and the banding was random such that it averaged away in master darks/bias.

 

having said that, if you are seeing banding in flats (rather than just darks or bias) then it could be a different problem. that sounds like a pretty significant signal.

 

i think besides using the supply that came with the camera, it might make sense to try a different PC, or directly connecting the camera to your PC w/o a hub, and finally to try higher quality USB cables. you can also get ferrite chokes to put on the USB cables to try to eliminate any noise being coupled into the cables.

 

i would think that 3.5s flats should be long enough to average out any flickering effects from the panel, but it might make sense to see what you see when using a narrowband filter and a very dim panel with 20-30s exposures, or even longer, just to put that to bed as a possible source of the banding.

 

rob



#9 AdamJ

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Posted 24 June 2022 - 03:30 AM

I have not noticed any banding with my QHY268M, which I have had since Spring 2021.

 

My challenge with the 268, which I love (and bought the 268C as well, but have not yet used), is moving dust spots between flat and light acquisition.   This is generally only a single spot, out of many, on the sensor cover glass.  I speculate that 16-bit sensors have many more problems with dust spots shifting on the sensor compared to 12-bit sensors when nothing is changed due to the noise floor being 16x lower making them visible.  Since day one, I have noticed many more spots on the 268 that would be near the sensor that those in 2 year use of my 183; again I suspect much lower noise floor being the cause, e.g. similar spots are their in the 183, but buried by the noise floor. 

 

Small changes on the 268 are noticeable than would be buried in the noise floor with my 12-bit ASI183mm-Pro (used for 2yr prior to the 268, with few flat issues).  I have made after the fact flat spot repairs (or changes to a residual spot on master light) using PixelMath that are sensitive to ~0.000010 differences, which is close a 16-bit step of 0.000015 (1/ 2^16), supportive of my quantization noise floor cause.  By comparison 12-bit step is a much larger 0.000244, of which a 0.000010 difference would not show up.

No thats not why you notice more dust its simply because of the greater sensor area making it more probable that you will see dust 16bit vs 12bit does not make the noise floor 16x lower. 

 

Adam



#10 Planetibo

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Posted 24 June 2022 - 04:46 AM

Hi!

I had a Horizontal Banding problem with a Sony A7s DSLR (same pattern of https://www.qhyccd.com/qhy600m-c/#b22) which was probably due to interference generated by a 12v > 7.8v voltage converter (https://www.aliexpress.com/item/33045814885.html).

 

Maybe you can try with another power supply to check if the banding is recurring?


Edited by Planetibo, 24 June 2022 - 04:49 AM.


#11 schellaj

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Posted 24 June 2022 - 09:38 AM

Contact the vendor, send your screenshots.  QHY can remote into your system and see if it's software, firmware, or hardware.

 

The banding is NOT normal and should be resolved to your liking.  You should not have to just live with it.

 

Just my 2 cents.  I had an issue with my QHY268M, they remoted into my device, determined it was hardware related and sent me a new one (even before they received the defective one to their shop).

 

Jason



#12 David Rosenthal

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Posted 24 June 2022 - 10:15 AM

Contact the vendor, send your screenshots. QHY can remote into your system and see if it's software, firmware, or hardware.

The banding is NOT normal and should be resolved to your liking. You should not have to just live with it.

Just my 2 cents. I had an issue with my QHY268M, they remoted into my device, determined it was hardware related and sent me a new one (even before they received the defective one to their shop).

Jason


Oh believe me. I have already contacted QHY. Cha gave me some things to try first. They feel it is interference. I’m going to try some other power/signal configurations and see what happens.

#13 David Rosenthal

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Posted 24 June 2022 - 08:19 PM

I just tried the camera on the bench, no light panel and using the power supply and cable that came with the camera.  The banding did not change at all.  Nothing I have tried has been able to make a dent in what I am seeing.  I have notified QHY of the new tests.  Hopefully something can be done.



#14 David Rosenthal

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Posted 25 June 2022 - 08:05 AM

Also, I just hooked up my 294M to the same power and usb cables and see no banding at all.

#15 David Rosenthal

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Posted 25 June 2022 - 12:37 PM

I was thinking perhaps this data is just super faint and would be resolved in a stack.  I shot 16 of them, processed tem in WBPP with a master bias and ended up with this.  Please take a look and let me know what you think.

 

This is the camera, by its self, sitting on a light panel, in a lit garage

https://pbase.com/dj...image/172715018


Edited by David Rosenthal, 25 June 2022 - 12:56 PM.


#16 pfile

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Posted 25 June 2022 - 01:19 PM

well as i mentioned above, if this banding is 1) random and 2) does not exceed the published read noise of the sensor, i think you are OK. but you have to do that measurement. hopefully QHY has published the RN vs. gain graph on their website.

 

rob



#17 David Rosenthal

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Posted 25 June 2022 - 02:18 PM

I used PI to measure the read noise and it is well within specification.  Using read mode 0 and gain 56 the read noise should be 2.07e or better.  PI reported a read noise of 1.529e

Attached Thumbnails

  • Screen Shot 2022-06-25 at 3.13.40 PM.png

Edited by David Rosenthal, 25 June 2022 - 02:19 PM.


#18 David Rosenthal

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Posted 25 June 2022 - 02:19 PM

Here is the read noise specification

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  • Screen Shot 2022-06-25 at 3.14.04 PM.png


#19 pfile

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Posted 25 June 2022 - 02:35 PM

i guess the other component of this is that autoSTF can make these bands seem much worse than they really are, since you're really zooming into the signal present in the bias/dark.

 

but that's only about the bias/darks. i do feel that if you see banding in a flat that something else is going on. i have definitely seen pattern noise in my flats with my CCD camera but these also appear in the master flat and i think they are reflective of the QE differences in the sensor from pixel to pixel. there's a structure to it.

 

if you blink your flats do you see the banding jumping around? i assume so since it seems to have averaged out in the master.

 

can you try sky flats/t-shirt flats to eliminate any flat panel flickering as the cause of this problem in the flats?

 

rob



#20 David Rosenthal

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Posted 25 June 2022 - 02:42 PM

I loaded up the flats into the blink tool and it looked like old school UHF Rolling noise on a TV set !!!



#21 David Rosenthal

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Posted 27 June 2022 - 12:26 PM

I am not entire sure what changed but it appears that the banding was indeed interference, from somewhere, I think the UPS I use on the imaging computer.  I had the camera and flat panel powered off that during the initial tests.  I was able to get out and try the camera under the stars.  I was playing with the spacing and after removing some mm shims the pick-off prism ended up in the FOV.  I did not notice until afterwards. 

 

This was shot with the FSDQ-106 at f/3.63.  There are some obvious spacing issues in this image and a bit of tilt.  I feel going forward I will image at the native f5 as there is no room for a tilt adapter.  Still loads of playing to do.

 

This is only 8*600 seconds in High Gain mode, gain 56, offset 40.  Bias and Flat calibration and EZSoftStretch only, no other processing at all.

 

I am really thrilled at the amount of fine detail in this frame.

 

Full resolution:
https://pbase.com/dj...image/172715969

50% Resolution:
https://pbase.com/dj...image/172715970

 

At 50% this is almost acceptable ... minus the prism flares which not be there going forward


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