[PixInsight] How to prevent Flat overcorrection?

Processing Calibration Deep Sky
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distantnova avatar
distantnova avatar
I'm not sure why, but my light frames are getting "overcorrected" by the Flat calibration process of the WeightedBatchPreProcessing script. Does anyone know why this happens and how I can prevent this? Is this maybe due to the large dark regions at the corners?

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dkamen avatar
dkamen avatar
When flats aren't working, it is either a problem with darks/dark flats (e.g. wrong gain/offset) or a general problem with your flat field (dew, stray lights, reflections).
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Chris White- Overcast Observatory avatar
Chris White- Overcast Observatory avatar
I recently helped someone with a similar issue on another thread.  It turned out that the flats were calibrated with frames taken with a different driver than the light frames.  Make sure you are using the same driver, gain, offset, etc… for the calibration (bias) frames used for preparing your master flat.
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Mike Cranfield avatar
Mike Cranfield avatar
It may help if we could see one of your flat frames?  From the image you have posted I am thinking perhaps dew on one of the optical surfaces when you took the flats maybe.
distantnova avatar
distantnova avatar
Turns out I was missing Bias and Dark frames - I took them with MaximDL instead of NINA as I did for the Flats and Light frames, but they had a different size (included the overscan areas), so the Lights (and Flats) were not calibrated with them. Now that I have cropped them, my fields are flat again smile
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Chris White- Overcast Observatory avatar
Chris White- Overcast Observatory avatar
Turns out I was missing Bias and Dark frames - I took them with MaximDL instead of NINA as I did for the Flats and Light frames, but they had a different size (included the overscan areas), so the Lights (and Flats) were not calibrated with them. Now that I have cropped them, my fields are flat again



That would do it.  Most of these large scale flat correction issues are due to mismatches with calibration frames.  Glad you figured it out.
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