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Hello, I need help with my stacked images. Last weekend I did my first attempts with the ZWO ASI 294MC Pro. Before I only worked with a Canon EOS 600. So I was very excited about the new camera. But after I stacked the images it shows a kind of halo or lense effect in the image I can not explain myself. I have uploaded the images here. The final and the original version. https://www.astrobin.com/391371/0/?nc=user https://www.astrobin.com/391392/?nc=user On my setup I use a Baader Coma Corrector. Maybe it's the cause of the effect. Please help or give some advices for futher experiments. Thanks, Daniel |
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| Can you post a link to a single sub FITS? Could be flat subtraction at fault or processing/stacking. |
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| Currently I'm at work but in the afternoon I will upload it. Can you tell me where to upload it |
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| Dropbox, Google drive, one drive. |
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| Also please describe your image processing routine |
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| I postprocessed the pictures according to the instructions of Kayron Mercieca from https://www.lightvortexastronomy.com/tutorial-example-m31-andromeda-galaxy---dslr.html. |
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| So did you follow this tutorial https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html to do the image calibration and registration? |
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| No, I stack my pictures always with Deep Sky Stacker. Lights as Kappa Sigma and Darks as Median. Dark Optimisation is enabled. I don't use any Bias Frames. Just Lights, Darks, Flats and Flatdarks. |
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Daniel: I suspect your flat subtraction could be responsible for the lighter image centre (I had a similar effect when the flats were too dark). A quick look at a few light subs will tell. Please upload a few light subs (FITS files) to one of those file sharing hosts and I will take a look. |
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Here are two links: first one is a Light Frame https://drive.google.com/file/d/1FRvyMyez8xElrT7BorLuFmwAfYb94QPL/view?usp=sharing second is a Flat Frame https://drive.google.com/file/d/1wQhNo8M5WGOWLEastjehxniRp2daTyYn/view?usp=sharing |
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Hi Daniel, I looked at both light and dark frames and I think the problem is not with your optical train but with image calibration routine (bad dark optimisation or too dim flats). The stretched light frame (a really nice sub), looks fine and does not show the halos you are getting in your processed images - just a normal vignetting pattern: https://www.dropbox.com/s/iu6uiudmdmhi3ft/M81_00001_d.jpg?dl=0 I suggest trying the following: 1) Disable dark optimisation, I had some strange results with it (similar to your halo) 2) Shoot brighter flats. Looking at your flat image I think it is too dim and may cause the halo when subtracted in DSS. The mean signal in the flat is 15000 ADU out of 65535 (max value in the light image). Ideally the flats should be between 50-75% of the max ADU (or ~40,000 ADU for your camera) 3) Try calibration in Pixinisight, it is superior to DSS: https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html Cheers, Alex |
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Thanks Alex. I will try your suggestion and take new flats. The dark optimisation is a I never thought about to disable cause it sounds like a optimisation which always helps. Now I will disable it and only use in special cases. Please tell me how you measured the ADU of the flat frame and what it's meaning? |
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Try disabling dark optimisation and check if it helps to remove the halos.Daniel: in Pixinsight - Process -> Image statistics Mean ADU shows the the average pixel value on the scale from 0 to 65535 For flats you want to be in a sweet spot of the detector - not too dark (otherwise you introduce extra noise) and not too bright (otherwise you will get artefacts arising from overexposure). A rule of thumb 50-75% of your max ADU |
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Hey Daniel, Wieso hast du keine Bias gemacht? Bei meiner ASI1600mmc funktionieren die Flats ohne Bias überhaupt nicht. Steht aber auch in diversen Foren. Die hast du doch schnell durchgerotzt. ;) Gruss Tony |
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Hallo Tony Ich habe bisher mit meiner EOS600 fotografiert. Da waren keine Bias notwendig. Daher habe ich bei der ASI294MC Pro auch (noch) keine Bias gemacht. Werde ich aber auch bei nächster Gelegenheit machen. Danke und beste Grüße Daniel |
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Hallo Daniel: Lies mal bei der Beschreibung zur Kamera da steht etwas bezüglich F / B https://teleskop-austria.at/ASI294MCP_ZWO-ASI294MC-Pro-Farbkamera-Diagonale-232mm-Auflosung#m und vielleicht helfen Dir die Ausführungen von Thomas Henne bezüglich Bildkalibrierungen weiter: http://www.distant-lights.at/tipps.htm Ansonsten: PI hat ja für den Anfang gerade mit dem BatchPreProcessing Script zum stacken ein einfaches Werkzeug, das in der Regel gut funktioniert. Und danach sowieso eine gute Backgroundextracktion (DBE oder ABE) angesagt. Siegfried |
