QHY128C Gain Question

umasscrew39
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QHY128C Gain Question

#1

Post by umasscrew39 »

Hi Robin

I was able to successfully connect my new QHY128C to SharpCap. QHY recommends a gain around 40 but most folks using this full frame camera recommend a gain of 2200 and an offset of 8 as they say 40 does not give good images and is very slow. However, the maximum gain setting I can get is 255. Is there a way to achieve a gain of 2200?

I just read a long thread on this issue with the QHY168C (QHY168c Gain Scaling question) and it gave me a headache and I am not sure if the issue was ever resolved.

Regards,

Bruce
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Re: QHY128C Gain Question

#2

Post by admin »

Hi Bruce,

This there was once a time when all Qhy cameras had a gain range of something like 0 to 50, and the gain was measured in dB. Then they added some new models and those new models had a range of something like 0 up to 500 and the gain was measured in tenths of a dB. At this point thing still kind of made sense.

What seems to have happened lately though is that lots of new camera models have been added without QHY bothering to calibrate the gain values properly. Instead of the gain is being measured in sensible units like dB, they are just numbers – probably just raw values that get sent to the cameras sensor chip with ranges like 0 up to 255 or 0 up to 4095. Unless you have the technical documentation for the sensor chip inside the camera then there's no way to know how much brighten the image be for a particular gain number in these cases. Well, not quite no way – you can run the sensor analysis tool in SharpCap which will make measurements to let it work out those figures. I would certainly suggest doing that with the most recent version of SharpCap 3.2 (I made some changes recently that should make this measurement more robust in cases like this where we have no idea to begin with what different gain values mean).

I'm afraid I can't help much with the reason behind the range being 0 up to 255 - SharpCap simply asks the qhy SDK software what range of gains is available and makes that the limits on the gain slider. It's possible that these limits may even change with different versions of the qhy SDK software – if you are using the latest SharpCap then you should have the latest version of their SDK software installed automatically (I would recommend never to install any 'SharpCap updates' from the qhy website – these would actually be likely to change you back to an older version rather than update you).

Cheers, Robin
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Re: QHY128C Gain Question

#3

Post by umasscrew39 »

Oh, boy- thanks, Robin

Well, it arrived yesterday and I still need to get the correct adapters to connect it to my C11"EdgeHD before testing it. I hope getting this camera was not a big mistake. I am assuming that doing the sensor analysis, I will find the correct gain setting to use to get great images with it.

I downloaded the camera driver from their site and I already had the updated version of SC. Are you saying I should delete the driver I downloaded from their site and then re-install the new versions of SC?
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Re: QHY128C Gain Question

#4

Post by admin »

Hi,

No keeping the driver installed is fine – the problem is things from qhy's website that claim to update or patch SharpCap – these should be avoided as they tend cause more problems than they solve. If all you've downloaded is the qhy driver and the later SharpCap all should be good.


Cheers, Robin
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Re: QHY128C Gain Question

#5

Post by umasscrew39 »

ok- excellent. I will figure what these numbers mean even if I have to do trial and error of taking images along with the sensor analysis. I'll post some data once I get it rigged up on my C11" in my observatory (remember, I am the 12ft up high guy, :D )
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Re: QHY128C Gain Question

#6

Post by umasscrew39 »

Hi Robin

I did not realize this before but if you connect to the camera via ASCOM driver within SC, the gain range is as expected, up in the thousands. However, you get a warning message that performance may suffer and that you may not have access to all of the features. That is correct as when I connected, not all of the features appeared on the screen. When I connected to SGPro via ASCOM, the gain controls are correct with no warning messages.

So.....

1- I am not sure why it seems to work via ASCOM in SGPro but not in SC.

2- Why the scale is different when directly connecting to SC. I sent this question to QHY but I am dubious I will get a response.

Again, once I get it hooked up on the scope, I will do the sensor analysis.

Finally, someone else on their forum asked the same gain question about the QHY168C (same person who discussed this with you on this forum, I think). After some back and forth, they left him with this graph to help identify the correct gain setting.
20180811061711315.png
20180811061711315.png (53.55 KiB) Viewed 7926 times

Bruce
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Re: QHY128C Gain Question

#7

Post by admin »

Hi,

Unfortunately Ascom doesn't give complete control of the camera – this is a particular problem for more modern CMOS cameras which have more settings that can be adjusted than older CCD cameras. Often you will find that the controls that are missing from the SharpCap user interface can be found in the Ascom settings window for the camera – obviously that's less convenient to adjust and also it means that SharpCap doesn't know the values of those controls and can't save and restore them in capture profiles for instance. That's the reason that SharpCap ones you when you try to use a camera that is directly supported via the Ascom driver.

Having said all of that, if the options you need are available in the Ascom driver and you don't need high frame rates then feel free to use it.

Seeing that gain graph, it will be interesting to find out what happens for gain values beyond 14 – you say that the camera seems to offer values up to 255. Please share your sensor analysis results when you have as it might help make sense of what is going on.

Cheers, Robin
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Re: QHY128C Gain Question

#8

Post by umasscrew39 »

Hi Robin

I am still waiting to receive spacers to get my backfocus set in order to run the sensor analysis. In the meantime, QHY sent me this response to my question:

In SharpCap you can set Gain: 1 for shooting.
In addition, let me explain why the gain range is different. First, the gain is divided into two forms of analog gain and digital gain. In the QHY camera, the single-frame software uses analog gain. At this time, the QHY128 gain range is 0-4027. The unit gain of 2200 is also obtained through the single-frame mode test.
The digital gain is used in SharpCap. The gain range is 0-255. Unit gain can be achieved when Gain: 1 is set in the software under digital gain. sharpcap can adjust the analog gain of each channel separately.


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Re: QHY128C Gain Question

#9

Post by admin »

Hi Bruce,

Does your camera have red/green/blue white balance controls available to adjust? If it does do they have the range of 0 to 4027 suggested by qhy? I have a horrible feeling that with this camera they have put control of the gain behind the white balance controls and then added (for some strange reason) a digital gain behind the normal analogue gain control! I must admit I wasn't expecting that!!!

Cheers, Robin
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Re: QHY128C Gain Question

#10

Post by umasscrew39 »

Hi Robin

Yes- to both of your questions. When I open the camera, the gain defaults to 10 and the R/G/B white balance is at midpoint. If I slide them to the far right they reach 4027. Changing the gain control to any other value does not effect the R/G/B max value of 4027. If I understand what they are saying, I need to keep the digital gain at 1 and then slide each R/G/B white balance slider to a specific setting???
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