I just upgraded from using an Nikon D5600 to using a cooled astro-cam: QHY 247C. I am still trying to find the best settings for the camera and while doing so, found some odd functionality with SharpCap. I took some lights using APT and set the gain to 2000 and the offset to 50 (based on user recommendations). I thought I would take some darks using SharpCap since its histogram is more helpful. However, I got what I considered to be an odd looking histo (way to much signal above the black peak). I checked the lights and the histogram showed the expected curve after the background (black) peak. So I took some darks with the same gain and offset settings using APT. The results looked a lot better to me.
I saved files taken with both apps as FITS and examined them using FITS liberator. The one taken with SC has a mean value of about 11000, while the one taken with APT has a mean value of about 200. The FITS headers show the same values for Gain and Offset.
The files are too large to attach, but I attached the camera settings for SC.
Is there an issue with setting the gain for the QHY 247C?
Sharpcap/APT different results on darks
Sharpcap/APT different results on darks
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- dark fms g-2000 off-50_00001.CameraSettings.txt
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Re: Sharpcap/APT different results on darks
Hi,
It's tricky to be sure as unlike the majority of other brands of cameras, QHY cameras seem to each have their own ranges for gain and other controls (like white balance). If you say '200 gain' for a ZWO camera, it always means 10x brighter than zero gain. If you say '200 gain' for a QHY camera it could mean anything (some only go to 60 gain, others like yours to 2000 and above).
Having said that, there are some things worth checking out...
1) The 247 camera has a 14 bit sensor. SharpCap always scales up to 16 bits, maybe APT doesn't, so if that is the case you might expect a maximum pixel value of 16383 in APT and 65532 in SharpCap files. That would account for a factor of 4.
2) The R/G/B white balance values of 51 don't look to be default values (those are normally 16, 64, 128 etc for QHY cameras - again they vary from model to model sadly). The best way to check this is usually to put the camera into 8 bit mode and then show the histogram and tweak the white balance values. Look for the value that doesn't put spikes or gaps in the histogram and you will have found the 'neutral' value. If the neutral value is 16 (for example) and you have 51, then the colour balance controls would be applying a digitial gain of about 3.2x to each channel.
cheers,
Robin
It's tricky to be sure as unlike the majority of other brands of cameras, QHY cameras seem to each have their own ranges for gain and other controls (like white balance). If you say '200 gain' for a ZWO camera, it always means 10x brighter than zero gain. If you say '200 gain' for a QHY camera it could mean anything (some only go to 60 gain, others like yours to 2000 and above).
Having said that, there are some things worth checking out...
1) The 247 camera has a 14 bit sensor. SharpCap always scales up to 16 bits, maybe APT doesn't, so if that is the case you might expect a maximum pixel value of 16383 in APT and 65532 in SharpCap files. That would account for a factor of 4.
2) The R/G/B white balance values of 51 don't look to be default values (those are normally 16, 64, 128 etc for QHY cameras - again they vary from model to model sadly). The best way to check this is usually to put the camera into 8 bit mode and then show the histogram and tweak the white balance values. Look for the value that doesn't put spikes or gaps in the histogram and you will have found the 'neutral' value. If the neutral value is 16 (for example) and you have 51, then the colour balance controls would be applying a digitial gain of about 3.2x to each channel.
cheers,
Robin
Re: Sharpcap/APT different results on darks
Can you remind me - do the white balance values actually change the values in the image file or are they just for preview? If the former, that could explain the difference. APT does not change the WB before storing the file. Some other info:
- 2200 is 'unity gain' for the 247C
- Both files show max values of 65532
Can you tell me the WB values that would not alter the ADU values from the camera?
Thanks!
- 2200 is 'unity gain' for the 247C
- Both files show max values of 65532
Can you tell me the WB values that would not alter the ADU values from the camera?
Thanks!
Re: Sharpcap/APT different results on darks
Nevermind! I figured it out. It was the WB settings. I set them all to 1 and now the files match.
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Re: Sharpcap/APT different results on darks
Hi,
good to hear that you found the difference. I would just check though that with the WB controls set to 1 you can still get fully saturated pixels in the image (ie values close to 65535). I don't think I've encountered 1 being the default 'neutral' position for a QHY white balance control before - it might be that it is, or that APT is defaulting the controls to 1 and now both programs are applying white balance that is making the image dimmer.
cheers,
Robin
good to hear that you found the difference. I would just check though that with the WB controls set to 1 you can still get fully saturated pixels in the image (ie values close to 65535). I don't think I've encountered 1 being the default 'neutral' position for a QHY white balance control before - it might be that it is, or that APT is defaulting the controls to 1 and now both programs are applying white balance that is making the image dimmer.
cheers,
Robin