Darks are not removing amp glow

[sharpcapmullet]

Using my QHY mono camera, no matter which exposure I use, the darks are not removing the camera's amp glow at all. I know the settings and temps all need to be same so I must not be clicking a button or two to make sure this is actually occurring. Maybe?

I turn everything on, set temp, wait 10-mins for it to settle, I check all the settings and exposure time, then I go to capture tab, the capture dark, save to capture, and then start the dark capture. No matter if I use the master dark or any of the individual darks, no effect at all when imaging has started and subtract dark is checked.

Am I missing something somewhere to correct this?

[Menno555]

Hello and welcome

This is a long shot (and I hope I don't insult you) but it happened to me when I was doing darks for the first time
Assuming you take darks during your capture session: did you cover the telescope with it's dust cap?

Menno

[admin]

Hi,

probably a good starting point is to look at the pixel values in the master dark and in the individual light frame image files (captured *without* dark subtraction) in the are of the amp glow. A utility like FITS liberator lets you view the pixel values in a FITS image file nicely, and also stretch both images so you can see the amp glow in them.

There should be a similar jump in pixel values from non amp glow regions to the amp glow regions in both the master dark and the individual unsubtracted light frames, although the light frame pixel values will be higher due to sky background, etc. With an appropriate stretch you should also be able to see the amp glow in both.

In this sort of situation it's always worth checking the camera settings match between the darks and the lights (exposure, gain, offset, colour balance, temperature, etc).

cheers,

Robin

[sharpcapmullet]

Thanks for replies, I have been imaging/live stacking for years, all of the parameters while taking darks equal those when imaging/live stacking.

I changed my workflow last night by not focusing right prior to live stacking and just hoping it was good enough. Typically I take darks at my desired exposure, take darks, slew to bright star, set the exposure at 5-seconds to check focus, adjust slightly if needed, and then set exposure back, slew to target and start live stacking.

By not doing this reduced exposure step, the amp glow was reduced by about 50% in intensity but it was still present.

I am completely stumped.

[Menno555]

To see if it's a SharpCap issue or not, could you try and use the light and calibration files to apply in another program like PixInsight, SiriL or something like that?
If you don't have any other program, you maybe could share files through WeTransfer (or something like that) so we can try and see.

Menno

[sharpcapmullet]

Pretty sure I eliminated Sharcap as the issue. The QHY spec page for the camera states “amplifier glow can be reduced during long exposure.” So last night I upped my exposure to 3-minutes and upped the number of dark stacks to 30, alas amp glow was almost totally removed. Now I have this weird circular halo thing going on instead but I could somewhat adjust that out with the histogram. Good enough for EAA.

[admin]

Hi,

good to hear you are making progress - might be worth sharing an image showing the weird halo - maybe someone would be able to identify it. It could be a number of things, but one that came to mind was possibly frost/dew on the sensor window?

cheers,

Robin

[GroupJ]

I am having the same issue with my QHY 183M. I took a set of 5 darks right before I started stacking, so camera settings were the same except for apply dark, light, and satellite trails don't remove. I was using a 3nm Ha filter in Bortel 7. Exposure was 180 sec, gain 40, offset 30, usb 30, temp -15c. Looking at the master dark, it looks solid black. The light stack shows strong amp glow starburst on right edge and soft glow around the edges.

Assuming this is not a Sharpcap bug, how can I improve my workflow? Do I need to take more darks in the stack? It wasn't clear to me what sharpcapmullet did in the note above to improve amp glow removal.

thanks for the help.

[admin]

Hi,

I think the first thing to investigate is why is your master dark solid black? Is it really solid black, or is it just dark and close to black? If you load the frame up into a FITS viewing tool that automatically stretches the image (say FITS Liberator) then you will see which of the two it is. If the frame is perfectly black (or there are pixels with zero pixel value in it) then maybe your black level/offset setting is too low so that the images from the camera are black level clipped.

It's often easier to see what is going on in this sort of case if you can share some of the file here - perhaps via a sharing site like Google Drive or Dropbox. Looking at the images often reveals things that are hard to detect in written descriptions.

cheers,

Robin

[GroupJ]

Robin,
Thanks for taking the time to help. Pretty cool the tool developer is helping me learn the tool!!!

so I am just learning so bear with me:

1. The master dark file I am looking at is in my folder/SharpCAP Capturers/darks/QHY183M/MONO16@5544X3684/180.0S/gain_40
2. When I double click the file it opens as a png file: MasterDark_5_frames-15.0C_2026-05-12T08_45_38.png and it “looks” solid black
Question: is this the “frame" I load into the FITS viewer? FITS liberator was not able to open this file.
If that is not “frame” to load - where do I find the correct frame?

As a note, I recently took a set of 40 darks at 180s exposure and saved the individual FITS. I loaded the FITS frames into ASTAP and created a master dark which clearly showed amp glow. Cloudy skies have prevented me from applying that dark to see if it works.

https://drive.google.com/drive/folders/ ... sp=sharing

I dropped the lights (showing strong amp glow) and darks into google drive. The gain_40 dark is the one used for the light. The gain_30 dark is the one that shows amp glow when loaded into ASTAP

Thanks for the help Robin

Al