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

Andreas
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Joined: Thu Jun 10, 2021 9:04 am

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

Post by Andreas »

Hello everybody,

I have now tested my QHY 268-C a few times in the starry sky and wasn´t completely satisfied with the expected results of this 16-bit camera, which has been praised in all forums.

To optimize the best exposure time and gain setting, I use the manufacturer's information as well as SharpCap's sensor analysis, which so far has always provided relatively suitable values ​​with regard to the manufacturer's information for my other cameras.

Unfortunately not so with the QHY 268-C. The comparison of the measured values ​​from SharpCap with the manufacturer's information shows significant differences in the system gain (50%) and also a too low Fullwell value (50%).

I have made the measurement in different configurations on the telescope and stand alone as well as with the diff. read modes of this cam. In the example attached, my favorite mode "High Gain Mode" has been selected, which is shown in the manufacturer diagrams, among others
corresponds to the dark blue curve.

Result: Unity Gain, i.e. e / ADU = 1, could not be achieved in any of the set modes. I´ve got a comparable result from a friend - same values.

Can you help me with this problem? Is it a buck of sharp cap 3.2 and is it solved in the future , or still judged in the beta version?
QHY Sensor analysis.pdf
QHY sensor analysis
(436.04 KiB) Downloaded 11 times
Thanks and best regards, Andreas
didiflei
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Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

Post by didiflei »

Hello Andreas,

on my QHY268C the analysis data is the same as yours. I still can't explain why there is such a huge discrepancy between Sharpcap and QHY.
In Cloudynights this issue was discussed once briefly, but without explanatory statement.
I would be really interested to know if the QHY268C really has such a high FullWell as QHY claims.

After 3 months of use, I am not completely satisfied with the recordings of the QHY268C either.

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

Post by admin »

Hi,

unfortunately I don't have a 268C to test with, but I have run tests on cameras from other manufacturers using the 571 sensor and had sensible results.

Have you tried running the analysis with 'Force Still Mode' set to 'On' in the camera controls on the right hand side? QHY cameras run by default in live video mode, and I wonder if some of the modes may not work quite as expected in video mode?

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

Post by didiflei »

Hi Robin

here would be a statement of the company QHY very interesting.
I have performed the sensor analysis in "live video mode".

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

Post by Andreas »

I´ve done it, but every time I got an error and SharpCap ends the session. See attachement
SharpCap error.jpg
SharpCap error.jpg (309.6 KiB) Viewed 194 times
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Andreas
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Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

Post by admin »

Hi,

Ok, that's not unexpected because there were some quirks of still mode that were not well handled in SharpCap 3.2.

Hopefully SharpCap 4.0 will do a better job, as I spent quite a lot of time trying to get those sort of things fixed - https://www.sharpcap.co.uk/sharpcap/sha ... s/4-0-beta

thanks,

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

Post by Andreas »

Thanks Robin, I will test ist soon

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

Post by Andreas »

Hi Robin,

can´t wait for it and tested it allready in 4.0 beta - same result, System Gain and Fullwell are about at 50% of the value that QHY delivers on their homepage. See snapshots attached

As you are a Top-Partner of QHY , would ypu please adress this issue. It could be very helpful for the users of this camera to know if its only a calculating problem of sharpcap.

Thanks a lot
Andreas
QHY 268-C - Highgain Mode- SharpCap 4.0 beta - Sensor Analysis.JPG
QHY 268-C - Highgain Mode- SharpCap 4.0 beta - Sensor Analysis.JPG (107.93 KiB) Viewed 149 times
QHY 268-C - Highgain Mode- SharpCap 4.0 beta - Camera Control panel.JPG
QHY 268-C - Highgain Mode- SharpCap 4.0 beta - Camera Control panel.JPG (82.37 KiB) Viewed 149 times
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Re: QHY 268-C sensor analysis delivers false SystemGain (-e/ADU) and Fullwell Cap.

Post by admin »

Hi,

OK, and do you get any different results in the other read modes? Or do you get those results in every read mode?

How have you set up the colour balance controls on your camera? Colour balance can act as a secondard gain, and SharpCap tries to set them to default (neutral) values at the start of the analysis procedure, but unfortunately for QHY cameras there is no single standard 'neutral' value - it varies from model to model.

The easiest way to check the neutral colour balance values is like this:

* Set up gain/exposure for an oversaturated image
* show the histogram
* adjust the colour balance controls - neutral is the smallest value for each channel that means that the histogram for your oversaturated image reaches all the way to the right of the histogram graph.

For my 294C, the neutral values are 16,16,16

thanks,

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

Post by Andreas »

Thanks Robin,

Yes I‘ve checked it also in the modes DSO and Ext. Fullwell
Same result , approx. 50% of System Gain and Fullwell data in comparison to the QHY diagramms. But Readout Noise and Dynamic Range are 100% ok

I will check and test the colour balance and come back with the results

Have a nice weekend
Andreas
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