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My first attempt at imaging M13 in Bortle 7 skies and I can’t seem to eliminate the background aberrations in PII. The image posted was done with DBE and some IC. M13 I posted the raw stacked master and flat and bias here: https://drive.google.com/drive/folders/1R5M8IVMYzyVe4VETdQfP5lW2Da6eFlLd?usp=sharing |
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| I'm not sure what you mean by "background aberrations" but I'll assume you mean aberrations tout-court. First, I shall not the poor tracking the resulted in the elongated (in the RA direction) stars. Secondly, you also have tilting (quite possibly) and back-spacing issues (The nexus should have 90.3mm backfocus from the back-end of the camera thread) that needs being dealt width, witness the field aberrations which should have been suppressed at that image scale. |
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Here's what I was able to come up with using your M13 data. I used DBE twice, which eliminated most of the gradients that were present in your version, although I was unable to remove every gradient, especially near the corners of the image, so in the end I just cropped the edges off. I suspect it could be a flats issue, so if your imaging train is still in the same layout, I suggest re-taking your flat frames and see if that eliminates the gradients on the edges. For my DBE settings, I used a tolerance of 10, smoothing factor of 0.3, radius sample of 20 and the amount of samples per row to 20. I then generated the samples, where I just moved any samples that were on any stars. I then used DBE again once I stretched the image with GHS, with the same settings, although I selectively placed more samples where I thought it was needed. I didn't use SXT as I didn't feel it was necessary for an image of this type of target. BXT did work to a certain extent, but it is evident where the trailed stars were left if you look closely. Here's my PixInsight workflow I used for your reference: DBE SPCC BXT NXT GHS SCNR DBE SCNR Correct Magenta Stars Script to remove the magenta background cast Curves Colour Balance Curves Contrast Enhancement HistogramTransformation ACDNR HistogramTransformation NXT Export as a 16-bit TIFF into Photoshop for final tweaks You have good data! You even managed to pick up some small background galaxies. There was a decent sized one near the bottom left-hand corner of the image, but due to the gradient I had to crop it out unfortunately. I haven't actually shot M13 yet, although I might try and see what I can do when Hercules rises high enough in the sky where I live in Australia. Zak  |
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| Thanks all for your help. |
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Looks like a good start. Looks like you have vignetting. Did you use flats to calibrate? Mike |
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This is your image resampled to 50% because of the file size restriction of Astrobin. I didn't use the flat, which should be applied to individual frames. Didn't use the bias either. So I cropped out the vignetting and then used DBE. Some of the edge stars are distorted, which may be a backfocus issue, but could be due to other factors. But BlurXterminator reduces the star size so much it really does not distract from the image. Not bad! Here is the process I used: crop to remove vignettes corners DBE Background neutralization Blurx Noisex at 75% Image solver (after transferring fits header from the uncropped original file) SPCC GHS Histogram transformation to lighten it up just a bit Curves for color Noisex again at 50% to clean up histogram Color saturation increase Let me know if you have any questions. By the way, I just did an M13 from some RGB data provided by The Astro Imaging Channel." Aside from the vignetting, which good flats could fix, your image is very similar.  |
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George, You image is really good. I was worried I didn’t have good subs. Thanks, Glenn |
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Elmiko: I used flats and bias frames to calibrate. I think my flats are a bit off and will have to redo. Glenn |
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| Shoot your flats at 25000 ADU's. |
