QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

didiflei
Posts: 20
Joined: Wed Feb 17, 2021 4:23 pm

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#21

Post by didiflei »

Hi Robin,

I have performed the test according to your instructions. Here is the result:
2021-06-24 10_24_29-QHY 268-C sensor analysis delivers false SystemGain (-e_ADU) and Fullwell Cap. -.png
2021-06-24 10_24_29-QHY 268-C sensor analysis delivers false SystemGain (-e_ADU) and Fullwell Cap. -.png (65.04 KiB) Viewed 2269 times
I cannot select the WB(R/G/B) controls smaller than 10.

best regards
didiflei
User avatar
admin
Site Admin
Posts: 13177
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#22

Post by admin »

Hi,

thanks for that - it looks like the default WB values for that camera are 10,10,10 - and, unusually, you can only boost the channels, not boost and lower them.

If you perform a sensor analysis, SharpCap will set the WB controls to what it thinks is neutral when you press 'Start'. After that, at the 'Select an area of the image ...' stage, set them down to 10,10,10 - then proceed with the analysis. I think that should give correct results.

I will update the code to set a default of 10 for the 268C for the white balance values.

cheers,

Robin
Andreas
Posts: 12
Joined: Thu Jun 10, 2021 9:04 am

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#23

Post by Andreas »

Here are my results, I´ve never got a picture like yours with one white peak on the right side ;(((

I couldn´t adjust the WB below 10 in each chanel
Sensoranalyse QHY 268 C.pdf
(392.88 KiB) Downloaded 90 times
Afterwards I´ve made a sensor analysis in HG Mode with a WB of 10 in all channels - seeems to be a better result, but I still couldn´t reach the System Gain and Fulwell documented on the QHY webside (only 75% of them) - Do I have to go below WB = 10?? How and does it make sense?
Attachments
Sensor Analyse HG Mode WB 10 SharpCap 4.0 beta.JPG
Sensor Analyse HG Mode WB 10 SharpCap 4.0 beta.JPG (92.7 KiB) Viewed 2260 times
User avatar
admin
Site Admin
Posts: 13177
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#24

Post by admin »

Hi,

those figures look correct to me for the high gain mode - you are getting a FWD of about 50ke, which matches closely with the data published for that mode on the QHY web site and the similar data published by other manufacturers using the same sensor (ZWO, etc).

I will consider adding a new stage to the sensor analysis that will test for and find the neutral white balance values before running the rest of the analysis - this would only need to run for QHY cameras as other cameras all have consistent 'neutral' white balance values across the various models made by a manufacturer.

Did you run a extended full well test with the R/G/B values dropped to 10? If so, what were the results? I must admit I am struggling to see an astro imaging use case where using the extended full well mode makes sense - gaining an extra 50% FWD is not worth the cost of doubling the read noise (doubling the read noise means that you need to take subs that are 4 times longer, which means that you will suffer with *more* saturation issues, not less...)

cheers,

Robin
Andreas
Posts: 12
Joined: Thu Jun 10, 2021 9:04 am

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#25

Post by Andreas »

Ok I will Check ist with Extended Fullwell Mode….

In Highgain mode with gain = 0 the diagram of QHY (blue line) shows a System Gain of 1 e/ADU (unity) and a FWD of 62 ke - my last results with WB=10 at gain=0 were 20% lower - doń`t know if I have to worry about it, but in my opinion the difference is too huge
Attachments
CE9EDDF7-6019-4474-9D74-A5FD828908DA.png
CE9EDDF7-6019-4474-9D74-A5FD828908DA.png (978.26 KiB) Viewed 2252 times
Andreas
Posts: 12
Joined: Thu Jun 10, 2021 9:04 am

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#26

Post by Andreas »

Hi Robin,

I´ve downloaded the latest version of 4.0 beta today and realized that you have allready changed the WB für QHY 268-C to 10 during the sensor analyses. Thanks for the quick response on this issue

I have done a measurement of mode #3 Extend Fullwell 2CMSIT (yellow curve) and the result is not far away from the QHY datas. Have al look at the screenshot
Sensor Analyse Ext FW Mode WB 10 SharpCap 4.0 beta.JPG
Sensor Analyse Ext FW Mode WB 10 SharpCap 4.0 beta.JPG (118.32 KiB) Viewed 2237 times
Best regards
Andreas
User avatar
admin
Site Admin
Posts: 13177
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#27

Post by admin »

Hi Andreas,

yes, those figures look promising. I did notice that the spec for the 268 extended full well mode made a claim of 'in excess of 75000e' (or something like that) rather than actually specifying an exact figure. I wonder if it varies from sample to sample? Also remember that the SharpCap figures are subject to random variability - the direct measurement that leads to the FWD is the e/ADU at minimum gain. This may vary by a small number of % if you do repeated runs.

cheers,

Robin
rockenrock
Posts: 68
Joined: Tue May 03, 2022 12:53 am

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#28

Post by rockenrock »

Robin,
This has been a very informative thread, in many ways. :roll:
On a bigger picture, if the sensor analysis is done with 'wrong' white balance (or other parameter), and the results significantly do not agree the manufacturer curves, then what is going to be the effect in imaging with SharpCap? Will SharpCap then recommend non-optimal setting for imaging, as in after brain is run?
I am a newbie for this part of SharpCap so I am just wanting to understand the interrelations and usage a bit.

Thanks,
Roger
User avatar
admin
Site Admin
Posts: 13177
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

#29

Post by admin »

Hi Roger,

potentially, yes.

The most likely problems will be that SharpCap will incorrectly think that the sensor has a higher bit depth than it does (for instance it might think a 12 bit sensor is 16 bit) and also that SharpCap may measure a higher read noise. The bit depth will not have a big impact on the suggestions from the brain, but an increased read noise could lead to longer than normal exposure recommendations.

Overall, it's best to avoid this problem if possible, and if you think it has happened, re-run the analysis with the controls at the correct neutral positions.

cheers,

Robin
Post Reply