Sensor Analysis

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

Sensor Analysis

#1

Post by rockenrock »

Hi,
I am trying to get a sensor analysis to complete. I have QHY168C, and using a LED light + diffuser, all powered by regulated DC power supply. I can adjust the DC voltage to adjust the brightness. The brightness is uniform, like a flat field. Using16 bit raw, debayer off.

I have run sensor analysis maybe 8 times (at different DC voltages) without completion. It gets to the gain stage, and starts at 1 and gets to 11 or 12 gain, then says sorry could not get the brightness to the correct level. I had the pixel value readout turned on, and monitored the value R, G and B values. I think SharpCap uses Red. At gain 14, where it was getting stuck, the red pixel readout went from around 22,000 ADU at 310ms. The ms seemed to jump a lot, ie 310 would maybe jump to 400ms. If it is trying to get to say 26K, it was not gradually adjusting the ms value, but bumps the time quite a bit.
My camera gain is 0 to 14. Is there a target gain when setting the brightness level.

Overall, can you think of anything to try?

Thanks,
Roger
rockenrock
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Re: Sensor Analysis

#2

Post by rockenrock »

After check Sensor Analysis again, when running the Gain checking, and it gets to 12, the msec and red (raw) ADU readout:
Msec Red(Raw) ADU
197 28.9k
170 29.2
146 29.8
126 29.2
109 29.3
93.6 28.9
93.6 30.2
93.6 13.3k
Then starts over at 256 Msec. I do not understand why the ADU stays flat when the exposure decreases, and then suddenly drop? Then after several times trying, sensor analysis says it cannot settle on the desired value.

So any solution for getting Sensor Analysis to complete?
Thanks,
Roger
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Re: Sensor Analysis

#3

Post by admin »

Hi Roger,

can you post the SharpCap log, captured after a failed analysis attempt.

This sounds like a problem that happens when the camera doesn't respond uniformly to exposure changes, and instead responds with step changes so (for instance) 300,310,320,330,340,350ms all give the same brightness but 360ms suddenly gives a big jump in brightness. I have seen this happen with exposures over 1s for some brands (which is why SharpCap prefers to run the analysis under 1s exposure), I've also seen it caused by bugs in the camera software/firmware. Anyway, the log will have enough info to confirm or disprove this theory.

There isn't really a way to stop SharpCap from getting up to gain 12 or above in the current code.

It might be worth trying to dim the light source and use longer exposures - this problem seems to be happening at high gain, which will be using the shortest exposures in the analysis routine, so maybe pushing those a bit longer might help (but will make the whole process slow...)

cheers,

Robin
rockenrock
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Re: Sensor Analysis

#4

Post by rockenrock »

Hi Robin,
Thanks for your reply and detail explanation.
I wonder why my QHY168c would have problems to make the exposure exactly as requested. If I want to image at 170ms or 146 or 126ms I would expect the camera to do that, and the corresponding ADU to be downloaded. Maybe their exposure time setting only has 4bit "resolution"!

I will try again with lower brightness. I can easily control it with my adjustable power supply. If not successful I will provide the log file.

As for tolerating longer exposures, it is okay. I spent more than 4 hrs failing sensor analysis multiple times. So if doubling or tripling one run, but with success it is acceptable.
Roger
rockenrock
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Re: Sensor Analysis

#5

Post by rockenrock »

Hi Robin,
I attach the log file for 6 times trying Sensor Analysis. All failed at different gain levels depending on the starting brightness (different milliseconds). The first run got closest to completing, but failed at 13 gain setting. The QHY168c has max 14 gain setting. Before starting it showed 975msec, the closest I could get to 1,000msec.

The other tries were lower and lower msec and failed at lower gain settings. This is what you expected.

Please check and give any advice what I should try.

Thank you for your help.
Roger
Attachments
Log_2022-07-23T05_59_10-6020.log
Roger 6 runs sensor analysis all fails
(674.54 KiB) Downloaded 24 times
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Re: Sensor Analysis

#6

Post by admin »

Hi,

SharpCap's target brightness for each stage is typically 65% of histogram (+/- 7.5%, so the range is 57.5 to 72.5%). If it can get the brightness into that range then it takes the measurement and moves on. If it fails too many times to get into that range then it gives up - that's what you are seeing.

Looking through the final steps in the log, I can see that Sharpcap is getting measurements of about 57% for exposures of 364,390, 406,412ms and of about 76% for 429,431,435,451ms - that's not how exposure is supposed to work, but it's not clear if it is truly related to the exposure being set wrongly by the camera or is something to do with the high gain value.

I can see from the log that you are running the camera in RAW8 mode for the analysis - that might be part of it as it will have an effect on the way the camera works. Try RAW16 mode, since that is the one you really want anyway for deep sky work. It also may be worth trying 'force still mode = on' in the controls as you could be suffering from an issue where the changes in brightness due to control changes do not appear for a number of frames after the adjustment is made.

It would also be worth trying manually adjusting the exposure in the range noted about with the high gain values set to see if you also see a jump in the histogram rather than a smoth change as the exposure is adjusted.

cheers,

Robin
rockenrock
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Re: Sensor Analysis

#7

Post by rockenrock »

The camera first loaded at 8bit, but I opened a profile that set it to 16bit, no debayer, force still mode to on, etc.

Yes, I will play around with some of those higher gain exposures and see what happens.

Getting ready to ditch all of QHY pretty soon if I keep having troubles. It is pitiful thinking that has the 168c driver named after one of their guide cameras. I take it as insulting my intelligence. A camera and it's drivers, should be helping me, not creating barriers.

Roger
rockenrock
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Re: Sensor Analysis

#8

Post by rockenrock »

Hi Robin,
Today I again tried sensor analysis, confirming I have Raw16 and force still mode ON. All attempts failed.
Today I manually set the exposures as per your above suggestion, at gain 9, and all settings same as when I was doing Sensor Analysis. I found 2 groups of means. I made the below post in the QHYCCD Facebook page. After the below I double checked using Maxim DL6 to control the camera (with same gain, etc). I got also 2 groups of means with Maxim DL6. The Fits headers all list the correct times (because it comes from the controlling software).
-- Perhaps you have some QHYCCD technical contacts that might give some insight.
-- Could it be the actual exposure time is correct, but the camera is not reading out the correct ADU?
++++++++++++
Anyone know any cause for this?
My QHY168c will not set the exposure correctly that I request. Using my light panel, set exposure (seconds) as below, and get Pixinsight Batch Statistics for Mean. Using SharpCap at gain 9, offset 10, 16bit Fits files.
You can see the first 4 files have one ADU level and the last 4 are at a different level.
.364s -- .48255 Mean ADU
.390s -- .48257
.406s -- .48261
.412s -- .48260
.429s -- .64444
.431s -- .64429
.435s -- .64430
.451s -- .64435
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Re: Sensor Analysis

#9

Post by admin »

Hi,

OK, that's good info as it confirms the issue as being in the QHY SDK (or camera firmware) as far as I can see. I had a similar discussion with a different camera manufacturer recently - they had run into the same issue in testing of a prototype camera and were very pleased that the analysis had found a bug in their camera that they might never have spotted otherwise!

One thing worth trying is that there are a couple of newer versions of the QHY SDK than the one in SharpCap (SharpCap currently using the April 2022 version). You can find the latest here : https://www.qhyccd.com/html/prepub/log_ ... d#22.07.25 (just released today). If you copy the qhyccd.dll from the download over the one SharpCap installs, you can test to see if the latest updates help improve matters at all.

cheers,

Robin
rockenrock
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Re: Sensor Analysis

#10

Post by rockenrock »

Hi Robin,
As you suggested, I downloaded the update QHYCCD.dll and replaced the one that is in the SharpCap x86 program directory. Same non linear results as before, just a little different because my light source was brighter today.

I was given the QHYCCD technical advice email. Sent the attached chart to show him clearly the result I am getting.
So now just waiting his reply.

Roger
Attachments
Exposure-ADU problem of QHY168c.png
Exposure-ADU problem of QHY168c.png (26.66 KiB) Viewed 404 times
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