Buzzard75 Posted November 22, 2020 Share Posted November 22, 2020 (edited) I've recently been having some issues with image calibration in Pixinsight. A few issues actually. Darks Issues: 1. I'm using darks that are exactly the same exposure length, gain, offset, and temperature as my lights. I have never had to optimize my darks before and my understanding is I shouldn't have to as long as I'm using darks with exactly the same properties as my lights. However, if I don't select optimize when calibrating my lights, then my images come out completely black with maybe a couple bright stars even after a stretch. When trying to stack in DSS, it throws up errors during registration that it can't find enough star pairs after the calibrations have been completed. This suggests there has to be something wrong with the FITS files, but I don't know what it could possibly be. 2. Some of my light frames will come out black after calibration with my dark master regardless of whether I select optimize or not. I can't see anything in the header information that would suggest why it works with some lights and not others even with optimize selected as stated above. 3. My darks are not calibrating out the hot pixels in my lights at all. I am having to do Cosmetic Correction to remove them. I have never bothered with CC before because the calibration with darks usually did a sufficient job for my level of laziness. 😁 The darks I was using are only a month old and worked for three or four of my most recent images without issue. I don't know why they have not worked for the last two images I have taken. I am currently retaking dark frames to see if new darks will correct the issue or if it persists. Any other insight would be appreciated. Flats Issues: 1. My flats don't calibrate out my dust donuts at all. They are present in my light images and I can see them in my flats, but they are still present in my lights after calibration and in some cases more exaggerated. My flats are 2-seconds long so should be sufficient length. I've used flats that were much shorter and some that were longer with no issues before. I'm wondering if the dark optimization of my dark flat frames is playing a role here as well, but my flats don't seem to suffer the same issue as my lights do when calibrating. 2. EDIT Forgot to mention the gradient. When calibrating with my flats, my images come out with a terrible gradient. The images end up darker in the center and significantly brighter towards the edges. This normally wouldn't be a problem because there is typically some vignetting in images, but mine are fairly flat across the field to begin with. Again, it's like Pixinsight is overcompensating in this regard. And for what it's worth, I'm currently using my QHY247C camera. Thanks in advance! Edited November 22, 2020 by Buzzard75 Link to comment Share on other sites More sharing options...
dodgerroger Posted November 23, 2020 Share Posted November 23, 2020 I can’t really comment on suggestions to the above as I am a mere beginner with pixinsight but have you tried stacking your images in a different program, APP or DSS. See if you get the same results. This will narrow it down to your issue 1 Link to comment Share on other sites More sharing options...
Laurin Dave Posted November 23, 2020 Share Posted November 23, 2020 Maybe experiment with adding a Pedestal in Pixinsight when you calibrate to avoid the black clipping.. and see if that helps .. 1 Link to comment Share on other sites More sharing options...
Buzzard75 Posted November 23, 2020 Author Share Posted November 23, 2020 1 hour ago, dodgerroger said: I can’t really comment on suggestions to the above as I am a mere beginner with pixinsight but have you tried stacking your images in a different program, APP or DSS. See if you get the same results. This will narrow it down to your issue See #1 under Darks. Yes, I've tried DSS and the result is the same or at least similar. When I try and stack in DSS it can't integrate the light frames because there aren't enough star pairs because the images are basically all black. That to me suggests it's a file issue and not a program issue. 1 hour ago, Laurin Dave said: Maybe experiment with adding a Pedestal in Pixinsight when you calibrate to avoid the black clipping.. and see if that helps .. I'm not familiar with Pedestal, but I'll look into it. Thanks! Link to comment Share on other sites More sharing options...
Laurin Dave Posted November 23, 2020 Share Posted November 23, 2020 Another possibility would be some kind of light leak affecting your darks .. maybe compare current ones with historic 1 Link to comment Share on other sites More sharing options...
wimvb Posted November 23, 2020 Share Posted November 23, 2020 And don’t forget to just look at the darks. At what level are the mean and median? What about the mean and median of your lights? 1 1 Link to comment Share on other sites More sharing options...
Buzzard75 Posted November 23, 2020 Author Share Posted November 23, 2020 2 hours ago, Laurin Dave said: Another possibility would be some kind of light leak affecting your darks .. maybe compare current ones with historic Darks look fairly similar to the previous ones taken about a month ago. See the notes below about the mean and median values. It may explain why they are slightly different. 1 hour ago, wimvb said: And don’t forget to just look at the darks. At what level are the mean and median? What about the mean and median of your lights? Mean and median of my darks is around 437 for my last set. Mean and median of my lights is around 334. Ruroh!!😖 For fun (and comparison) I looked at the mean/median of my darks from a session a month ago and they are around 873. The lights were around 985. Based on those two sets of values, it would seem something is amiss with my last set of data. Actually, my last two sets of data as my lights for the previous set had similar values. Of note would be that I used a mini PC to capture my last two sets of data whereas all my previous sets of data used my laptop. I am running different versions of APT on both as I had issues with the most recent version on my mini PC. Short of exposing longer I'm not sure how to increase my mean and median. Unfortunately, with my poor guiding at the moment, I don't know that that is possible. Obviously increasing gain isn't an option as that would just increase my gain required for my darks. However, it make sense now why optimizing darks is the only thing that seems to work. Link to comment Share on other sites More sharing options...
wimvb Posted November 23, 2020 Share Posted November 23, 2020 For cmos astro cameras, you not only set gain, but also offset. Offset is to make sure that you won't get any negative/clipped pixel values. You should probably check if offset has changed. You can add offset before image calibration, at least in Pixinsight. A change in offset can also be the reason why your flats aren't working. 1 Link to comment Share on other sites More sharing options...
Laurin Dave Posted November 23, 2020 Share Posted November 23, 2020 I’d look at your files and check the fits header to see if gain and offset have changed 1 Link to comment Share on other sites More sharing options...
Laurin Dave Posted November 23, 2020 Share Posted November 23, 2020 Just now, wimvb said: For cmos astro cameras, you not only set gain, but also offset. Offset is to make sure that you won't get any negative/clipped pixel values. You should probably check if offset has changed. You can add offset before image calibration, at least in Pixinsight. A change in offset can also be the reason why your flats aren't working. Snap! 1 Link to comment Share on other sites More sharing options...
Buzzard75 Posted November 23, 2020 Author Share Posted November 23, 2020 (edited) Take a look. As best I can tell everything is identical as far as the imaging properties go. Gain, temp, exposure. I don't see anything for offset specifically beside BZERO. Lights Header: Image #1 SIMPLE = T / file does conform to FITS standard BITPIX = 16 / number of bits per data pixel NAXIS = 2 / number of data axes NAXIS1 = 6088 / length of data axis 1 NAXIS2 = 4052 / length of data axis 2 EXTEND = T / FITS dataset may contain extensions COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H BZERO = 32768 / offset data range to that of unsigned short BSCALE = 1 / default scaling factor OBJECT = 'NGC7380 ' / The name of Object Imaged TELESCOP= 'iOptron ASCOM Driver for Mount' / The Telescope used INSTRUME= 'QHY247C-e5af9d4d873698c45' / The model Camera used DATE-OBS= '2020-11-22T01:22:42' / The UTC date and time at the start of the expo HIERARCH CAMERA-DATE-OBS = '2020-11-22T01:22:42' / The UTC date and time at the EXPTIME = 180. / The total exposure time in seconds CCD-TEMP= -10. / Temperature of CCD when exposure taken XPIXSZ = 3.91 / Pixel width in microns (after binning) YPIXSZ = 3.91 / Pixel height in microns (after binning) XBINNING= 1 / Binning factor in width YBINNING= 1 / Binning factor in height XORGSUBF= 0 / Sub frame X position YORGSUBF= 0 / Sub frame Y position EGAIN = 1. / Electronic gain in e-/ADU FOCALLEN= 1624 / Focal Length of the Telescope in mm JD = 2459175.55743056 / Julian Date SWCREATE= 'Astro Photography Tool - APT v.3.84' / Imaging software SBSTDVER= 'SBFITSEXT Version 1.0' / Standard version SNAPSHOT= 1 / Number of images combined SET-TEMP= -10. / The setpoint of the cooling in C IMAGETYP= 'Light Frame' / The type of image OBJCTRA = '22 46 51' / The Right Ascension of the center of the image OBJCTDEC= '+58 03 10' / The Declination of the center of the image SITELAT = / The site Latitude SITELONG= / The site Longitude AMB-TEMP= 10.7 / The Ambient Temperature FOCUSPOS= 8250 / Focuser position in steps GAIN = 2200 / The gain set (if supported) BAYERPAT= 'RGGB ' / The Bayer color pattern Darks Header: Image #1 SIMPLE = T / file does conform to FITS standard BITPIX = 16 / number of bits per data pixel NAXIS = 2 / number of data axes NAXIS1 = 6088 / length of data axis 1 NAXIS2 = 4052 / length of data axis 2 EXTEND = T / FITS dataset may contain extensions COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H BZERO = 32768 / offset data range to that of unsigned short BSCALE = 1 / default scaling factor INSTRUME= 'QHY247C-e5af9d4d873698c45' / The model Camera used DATE-OBS= '2020-11-22T16:28:11' / The UTC date and time at the start of the expo HIERARCH CAMERA-DATE-OBS = '2020-11-22T16:28:11' / The UTC date and time at the EXPTIME = 180. / The total exposure time in seconds CCD-TEMP= -10. / Temperature of CCD when exposure taken XPIXSZ = 3.91 / Pixel width in microns (after binning) YPIXSZ = 3.91 / Pixel height in microns (after binning) XBINNING= 1 / Binning factor in width YBINNING= 1 / Binning factor in height XORGSUBF= 0 / Sub frame X position YORGSUBF= 0 / Sub frame Y position EGAIN = 1. / Electronic gain in e-/ADU FOCALLEN= 1624 / Focal Length of the Telescope in mm JD = 2459176.18623843 / Julian Date SWCREATE= 'Astro Photography Tool - APT v.3.84' / Imaging software SBSTDVER= 'SBFITSEXT Version 1.0' / Standard version SNAPSHOT= 1 / Number of images combined SET-TEMP= -10. / The setpoint of the cooling in C IMAGETYP= 'Dark Frame' / The type of image SITELAT = / The site Latitude SITELONG= / The site Longitude GAIN = 2200 / The gain set (if supported) BAYERPAT= 'RGGB ' / The Bayer color pattern Edited November 23, 2020 by Buzzard75 Link to comment Share on other sites More sharing options...
wimvb Posted November 23, 2020 Share Posted November 23, 2020 (edited) You may need to experiment, it seems. Similar to this Edited November 23, 2020 by wimvb 1 Link to comment Share on other sites More sharing options...
Buzzard75 Posted November 23, 2020 Author Share Posted November 23, 2020 16 minutes ago, wimvb said: You may need to experiment, it seems. Similar to this Thanks! Will definitely check it out. Link to comment Share on other sites More sharing options...
Buzzard75 Posted November 24, 2020 Author Share Posted November 24, 2020 @wimvb, @Laurin Dave, @dodgerroger, Appreciate all the input. I haven't figured it out yet. I took new darks, new flats, and new dark flats the day after I imaged so them being old wasn't really an issue. I have used Pixel Math to fix the symptom rather than the cause per that video series, or so I thought, but the end result didn't really change all that much. I can get a decent individual sub calibrated, but when they're all stacked it just isn't right. I still think there's something wrong with my dark frames which is making it worse. I'll just have to keep at it. 1 Link to comment Share on other sites More sharing options...
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