Image calibration help

[tomtom2245]

I'm running into a problem when trying to calibrate my Ha frames in Pixinsight. I'm using an ASI178MM-Cool which I know has some serious amp glow at longer exposures but up until this point, darks have been able to remove it quite successfully. The current problem is that the amp glow from the lower left and lower right is not being removed but the other parts are. This problem is not happening with my Oiii frames and they are actually 300 sec vs my 240 sec for Ha. I've tried image calibration several times and always get the same result. I also tried retaking the darks and still get the same results. The current darks were taken at the same exposure (240sec), gain (279), and temp (-15C). In the attached image, the upper left is an uncalibrated light frame, upper right is a calibrated light showing the amp glow still present in the lower corners, and the bottom image is my master dark and all three have an STF applied. The unstretched master dark does not show any signs of amp glow, only when I apply an STF do I see it. Any thoughts as to why it is not being removed? Oh, and during the calibration process, I leave Calibrate and Optimize unchecked in the darks section of the Image Calibration tool in PI.

[John_Gill]

Hi,

mmmh, that is some serious amp glow.  Firstly try reducing the cooling to -5 or -10 and see if the amp glow is still so severe.  Darks will not fix the amp glow but Flats should.  Can you reshoot the Flats?  Most likely the focus and optical train will have changed and your flats might not be the same.  I have "cheated" and used flats from different sessions and had a little success in removing unwanted artifacts.

When doing the ImageCalibration, the Bias does not need to be calibrated and the Darks and Flats are already calibrated and only the Master Dark needs to be Optimized to ensure that the Master Darks match the Lights.

space is not black
John

[bulrichl]

@tomtom2245:
The amp glow is the "starburst" in the upper right corner. By calibration it is obviously removed completely. I doubt that the remaining artifacts in the lower corners are amp glow, this seems to be a different artifact. Very strange that these artifacts only occur at the lower corners -- I haven't seen something like this before.

@John_Gill:
Darks WILL fix amp glow, Flats have nothing to do with it.

For the calibration of images produced by a camera with CMOS sensor, you will not need bias frames or a MasterBias, unless you use the MasterBias for the calibration of the flat frames in case of no flat-darks are captured. The darks or the MasterDark shall not be calibrated at all. When these suggestions are followed, the settings that the OP used for light frame calibration ("Calibrate and Optimize unchecked in the darks section of the Image Calibration tool in PI") are correct.

Bernd

[tomtom2245]

@tomtom2245:
The amp glow is the "starburst" in the upper right corner. By calibration it is obviously removed completely. I doubt that the remaining artifacts in the lower corners are amp glow, this seems to be a different artifact. Very strange that these artifacts only occur at the lower corners -- I haven't seen something like this before.

@John_Gill:
Darks WILL fix amp glow, Flats have nothing to do with it.

For the calibration of images produced by a camera with CMOS sensor, you will not need bias frames or a MasterBias, unless you use the MasterBias for the calibration of the flat frames in case of no flat-darks are captured. The darks or the MasterDark shall not be calibrated at all. When these suggestions are followed, the settings that the OP used for light frame calibration ("Calibrate and Optimize unchecked in the darks section of the Image Calibration tool in PI") are correct.

Bernd

The reason I suspect amp glow for all of the corners is I see this exact same pattern in all images shot with this camera, ASI178MM-Cool, and the severity of it increases with exposure time. The odd thing about it not calibrating out this time is I took Oiii images with this camera at 300sec and all artifacts, including the ones in the lower corners, calibrated out just fine but for some reason the Ha frames won't calibrate out. I've previously done an Ha-LRGB image with this camera and had no problems then either. It only appears to be my Helix Nebula Ha frames. I did some digging around and found a thread on I believe it was Cloudy Nights about amp glow with this camera that exactly resembled mine. There was some speculation that due to the temp sensor of this camera not being directly on the sensor, that even though you set the cooling temp to the exact same value, differences in ambient temp may impact your darks.