Image Calibration Issue
- michael_murphy
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I was imaging M13 a few nights ago and have encountered an issue calibrating the frames.
I have included a screen shot below. The images are from top left, clockwise. A calibrated light, the master flat, the histogram for the master flat (centered on .3139) and the uncalibrated light.
The calibration seems to have gone a bit odd around the edges of the dust bunnies.
Have you seen this before?
I have processed the images in Pixinsight.
Thanks for any help,
Michael.

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- Kinch
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I never saw anything like that before.
I used to use PI all the time for everything - now I use APP for stacking and calibration.....so I may be a bit rusty on this.
What would be of great help though would be the workflow you are using....and perhaps a screen shot of the Image calibration window: This one.....
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- michael_murphy
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The calibration screen looked like the screenshot below.
I took the flats two days after the lights and I was talking to someone who suggested that the camera might have moved slightly between taking the lights and flats or that the filter wheel did not move back to exactly the same position when I took the flats.
For the next imaging run I will take the flats immediately after the lights so see if I can rule out the camera/filter wheel moving between the two.
Michael.
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- Kinch
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When I was using PI for calibration, I was lucky not to have to use Darks......so I Bias calibrated my Flats when making a Master Flat. I then just calibrated my Lights with just that Master Flat.
In your calibration screenshot you are using both Bias & Dark calibration frames .....but as far as I know the Dark frames also contain the Bias.....so you should try it again without any Master Bias on that page.
So, I would try it in stages.....If you don't have FlatDarks - then calibrate the Flats with the Bias to make a Master Flat.
Make a Master Dark from darks with the same exposure time, temperature and ISO speed of the light frames.
Then use the Master Dark & Master Flat (ONLY) in that Image Calibration window.
I am not too well up on this....so I am open to and accept correcting if I am wrong. If nobody chimes up....then while you are waiting on your next imaging run....give the above a go....see if it makes any difference.
Brendan.
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- richardsweeney
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- Kinch
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This is from a Doc I got a long time ago....Jim's PixInsight Cribsheet. Search for that on the internet and you will find the guys website.....he will send out the full document if asked.
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- michael_murphy
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Kinch wrote: In your calibration screenshot you are using both Bias & Dark calibration frames .....but as far as I know the Dark frames also contain the Bias.....so you should try it again without any Master Bias on that page.
Thanks Brendan,
I followed Warren Keller's instructions for creating the calibration frames.
The master flat was calibrated against the master bias and master dark. PI calibrated the master dark to match the exposure of the flat frames.
I'll try what you suggest and PI's script to do everything to see if that makes any difference.
Michael.
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- michael_murphy
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I compared some of the lights and flats using dynamic crop and it does look like the camera moved between the two sets of images. I'll see if i can use Pixelmath to 'move' the position of the dust bunnies on the flats.
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- Kinch
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Brendan.
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- michael_murphy
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- Kinch
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Brendan.
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- michael_murphy
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- richardsweeney
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