Issue with flat frames [Deep Sky] Acquisition techniques · Marco Pegoraro · ... · 8 · 304 · 4

Hello everyone, I need some advice about flats.



A few months ago, I switched to a monochrome camera with an IMX571 sensor (ToupTek ATR2600M), paired with a ToupTek filter wheel and Antlia LRGB filters. As my main telescope, I use an Askar 103 APO.



I capture everything with N.I.N.A., using the Flat Wizard, and I’ve tried making flats both with a white T-shirt over the telescope and with a light panel.



Lately, however, I’ve been experiencing a problem: the flats seem to overcorrect the lights, causing noticeable artifacts in the final master. I perform the entire stacking process using WBPP in PixInsight.



I was wondering whether the issue might be due to some incorrect setting in WBPP, or if the flats (or calibration frames in general) are not being captured properly.



For calibration, I use:



• Flats peaking at 33% of the histogram

• Flat darks with the same exposure as the flats

• Darks with the same exposure and temperature as the lights



Additionally, I was wondering if there is a way in PixInsight to correct or at least mitigate the artifacts caused by flat overcorrection.



Thanks in advance!



PS

I’m attaching screenshots of the master light, master flat, and master dark, all with STF applied, as well as a file after combining the RGB channels.

Im not an expert (yet) but it looks like your master flat has some dust on there and they come somewhat onto your corrected master light. Do you take flats for each filter separate? It looks like one of your filters might have dust and if you use that on all other lights (that dont have dust on the filter), I can imagine the artefact coming in your master light...  Just a thought.

CS!

I concur - light leaks are a pain....

You have to be extremely thorough, a good test for me was to do a 5-minute exposure in direct sunlight during the day. If I saw nothing in my frame - I knew I had found my leak. 

The cleaning part is "easy" 
I use "Pec Pad's" and eclipse optic cleaning fluid. That has until now worked for me.

Unless I am missing something, did you also take bias/offset frames?  I've found that my flats overcorrect without these.

It seems I’ve found the problem. After disassembling and cleaning the camera, reducer, filter wheel, etc., I noticed that there were eight M2.5 holes on the front side of the filter wheel. I took eight screws and sealed the holes. I then tried taking some flat and dark frames, even under very bright light sources, and the issue seems to have disappeared. 😎