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After wrestling and struggling to image dso's with my ASI 290mm (planetary camera) and tiny fov, I finally got a cooled dso camera, the 1600mm pro. What a difference! I'm attaching my first effort (M81). I know I have a long way to go, but would appreciate some advice. My subs were all properly calibrated with darks only. I have not ventured into flats yet, but I will very soon. I suspect that is part of the problem with this image. The setup is Celestron Nexstar 8se, CGEM II mount, ASI 1600mm, 6.3 focal reducer, EFW and EAF. ASI 120mm guide camera.
What has caused the milky halo here? Regardless, I am thrilled with the results for my first try with my new camera. I also got a bunch of good data on M101 last night, which I have not processed yet. This image is 15 60sec subs each in LRGB, and 10 5min subs in Ha.
@edwallace Ed, does the halo also show up on the lights when you stretch them a lot? Or perhaps in the darks and/or master dark? I occasionally still use an ASI1600MM as well and have been using it in the part two years and have not seen such a prominent halo.
Yeah, that would be really, really weird vignetting.
@edwallace OK this clearly shows that the ring is present in the lights. You'll need flats to correct for that.
@wvreeven That confirms my suspicions. We've just begun a run of many cloudy nights here, so I will take flats soon. Thank you for the info.
@wvreeven I spent most of today, off and on, working on this. I took flats and darkflats to calibrate them. In the end, the artifact is still in the image, but it is greatly reduced. This was my first attempt at using flats. I suspect I need better flats - maybe a better light source (I used a white screen on a tv). Still, it is progress.
Not sure if that would be the issue, but a TV might put out a different spectrum from what you want in a flat (broadband), people sometimes also have issues using a tablet for instance. The ring seems optical though, but may be worth trying a different light source like a sky flat or an actual flat-box.
