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feilimb

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About feilimb

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    http://ronnach.wordpress.com

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    Male
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    Angling, Software, Astronomy, Film
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    Cork, Ireland
  1. @Oddsocks OK that is a bit of an eye opener for me on dust bunnies, I'm learning so much from every post you make on this thread! In the original post of this thread, the calibrated M51 image shows what appears to be a 'beveled' / 3D-like dust bunny. When I started this thread however, one of my original issues was that the exposure time of the flats was too low, with the ADU / histogram peak being much too far to the left (and those 'too dark' flats were used for the original M51 in op). It might however indicate what you are suggesting in a shift in focus.
  2. Many thanks for the time invested in the post above, I'm sure with all of the suggestions I will eventually get to the root cause! The issue now is waiting for the next clear night, the camera has since been detached from the OTA and focus changed on OTA. In my setup I typically have taken the night-time light frames (recent sessions outdoor air temperature would have been ~3 degrees C), then transferred telescope indoors and rested on the wooden floor of a first floor bedroom, before getting around to flats acquisition the following evening (~24 hours later). The temperature indoors would of course be much higher around 16-20 degrees, and possibly heat rising from ground floor. Focus was locked during imaging session and left in locked position afterwards. What made me think that focus had not shifted however was the fact I could see the most obvious dust bunny at top left of light frames, and see the same dust bunny in what appears to be the same size in the flat frames (see your Image 3 above). If the focus had shifted I assumed this dust bunny would be larger or smaller in the flats, than it was in the lights. Whenever the sky clears up here again, the plan is to go with 90 degrees rotated camera and use same flats acquisition process to see if the 'problem' rotates, and therefore might be attributed to internal reflections. I cannot see any obvious place where light could be leaking in from the focuser tube. I may also try taking the 0.85 field flattener out of the equation also, on a subsequent night in case the use of the flattener is contributing to the poor flats..
  3. Thanks David, that sounds very much like the issue I am having - using the flats is making the stacked image worse than if I don't use my flats at all. Thanks William, this is really useful. I guess before I try sky flats my first port of call will be to try rotating the telescope 90 degrees and retake flats with the TFT monitor & paper - at least to identify if my issue is internal reflections or not, I will report back in the next few days on this..
  4. Thx David yes maybe I will try some daylight flats. I have not tried capturing them before, do you know if one simply points scope to the sky and then capture? Or does sky colour matter, eg. blue sky vs gray sky?
  5. Thanks again William for the advice, that is a great idea to just rotate the scope 90 degrees and capture some flats to see if the red darkened area stays in same position in the frame or moves by 90 degrees. Maybe internal reflections are the most likely at this point, I guess I could also try to capture some sky flats to see if they produce a better result. I have been using Deep Sky Stacker, but also tried stacking in Pixinsight and got the same end result.
  6. Sorry for digging up this thread again, but in the meantime I tried capturing some new light and flat frames of M101 last week. This time, I started using plain RAW format (not FITS) with my Canon 450D, so all files (lights and flats) are 'CR2' files, and all have the same dimensions (4290x2856). I am unfortunately continuing to get the same horrible red area on right hand side of stacked images, which still appears to be coming from the flats. The flats are now being taken with camera in AV mode, pointed at TFT monitor with white screen and 2 sheets of A4 paper between monitor and end of my refractor (paper being rotated between each frame). The flats are taken at night in darkened room. I have attached one of the RAW flats via WeTransfer here: https://we.tl/g348Q7h0rj A stacked image continues to look similar to the previous example of M51 at top of this thread. When I extract the RGB channels from a single flat frame, the red channel (stretched) looks like this: Note on right hand side there is a much larger darkened area (beyond normal vignetting) than there should be. Does anyone know if this is a flaw in the camera? It is consistently there in every flat image I take. Could it be amp glow, or does amp glow only occur in long exposures? It's very annoying as basically means I cannot use flats currently when stacking an image until I figure out what the root cause is..
  7. APT Plate Solving Not Working

    I have never used APT => does the "Recalc" button over to the right of the focal length label allow you to regenerate the correct FOV?
  8. APT Plate Solving Not Working

    This website is very useful for calculating FOV for telescope and camera combinations: https://astronomy.tools/calculators/field_of_view/ Feeding in the Skywatcher 150, and Canon 550D to the above the following is generated, note the Field of View highlighted by the arrow: The field of view of 1.7 x 1.13 degrees is approx 70' x 68' (arc-minutes) which does not match the screenshot you attached above for APT (the screenshot of APT seems to show 15x8 arc-minutes). Is it possible to enter those FOV values into APT?
  9. Just a quick update, I tried recapturing flats tonight using Ekos, with a 1.3s exposure time at ISO100 (the exposure time which AV mode seemed to go with). Again however the histogram seems underexposed, and when I tried stacking the same ugly red gradients appeared in stacked resulting image. I wonder if this is somehow related to the fact that the Canon 450d is a 14 bit camera, but the FITS files saved by Ekos are 16-bit monochrome, and something is getting confused along the way.. In any case at this stage I've come to realise that I will take all future light, flat, bias etc. images in the native 'cr2' format, and this should make capturing and stacking of flats possible without any complications. I'll just have to put the few hours spent on M51 and the Rosette down to the learning curve Once the moon plays ball and the skies clear I'll try M51 again from scratch. Thanks again William for all your help, it was very much appreciated!
  10. You might be onto something there William, thanks again for taking the time on the above posts. I think you are right in that I need to go back to Ekos and try to achieve the flats again with that. At the worst, I can take an AV flat manually, look at the exposure time that was used / calculated by the on-board camera software, and then manually feed that into Ekos and triggering it to take exposures of the same length. I'll report back hopefully next time with a better final outcome!
  11. Hi all, so just an update - tonight I used the 2 sheets of printer paper in front of TFT monitor and took flats manually in darkened room with the AV setting on the camera. The histogram on the camera looks good with the peak very much close to centre / slightly to the right. OK so now the next complication When I loaded up the new flats in Deep Sky Stacker, and tried to start a new stacking process, the following message appeared: "The checked pictures are not compatibles (width, height, number of colors, number of channels, only one master dark, offset and flat." Then I noticed something unexpected in DSS in the view showing the list of images - my bias and light frames (FITS captured via Ekos) have a size of 4272 x 2848, whereas my CR2 flat files have a size of 4290x2856. At first I couldn't understand how this could be, but now I realise when I configured the sensor size for the Canon 450D in Ekos, I manually entered 4272 x 2848 (after consulting a tech spec online which stated this was the sensor size - I guess it was wrong). In any case, the images I have captured via Ekos must be slightly 'cropped' in comparison to the full dimension which is available. I thought maybe I can crop the flats I just took such that they are same size as the lights, and the dust bunnies line up but I'm getting stuck on the cropping (centre cropping approach does not line up, or taking the extra 18x8 from right hand side also not lining up the dust bunnies). I'll try play around with the cropping approach for a bit longer to see if I can get the size of the flat files to match the lights, and be 'aligned' with them also. Once I have done this however, I fear DSS will still show the same dialog/message as I have a mixture of monochrome 16-bit FITS files (not yet debayered) and RGB CR2 Raw files... aaarghh is there no end to the complications of this hobby!
  12. @carastro@Stub Mandrel Thanks for the screenshots with samples of histograms to expect in the flat images. I just have a question on when you take these with the 'AV' setting on the camera, do you change the exposure compensation dial on the camera (not sure if that is the right term, but it is the dial that has values like -2, -1, 0 +1, +2). I seem to recall reading some time back about using the AV mode, but having to adjust the exposure compensation to either positive or negative value, but maybe this is not necessary in any case?
  13. Many thanks William for the brilliant diagnosis and advice. I have a few things to try now and it just struck me this morning that I think the camera body is still connected to the OTA since I last captured the flats/lights a week ago - so in theory I can try obtain the flats again from scratch for calibrating the M51 / Rosette subs. I'm fairly sure the monitor is a TFT display (it is definitely not CRT), so I will probably try diffusion paper with the 'AV' setting on camera approach and adjusting screen brightness as you suggest to try get an exposure length of 1second+. I never knew of the issues with monitor usage as a source of light - there was me thinking this is a very convenient way to do it ... I'll try to recapture the flats tonight using all the suggestions above and hopefully will report back with an improved master flat & stacked image afterwards
  14. @Oddsocks Hi William, many thanks for the lengthy reply I'll do my best to answer the questions. Sorry I was probably a bit unclear in the original post on a few points so I'll try to go through them.. I guess something was messed up when capturing the flats as you suggest, I have only recently started trying to use flats so must have had an error on capture or something like that. I use the software 'Ekos' for capturing of flats, and did not look at the histogram at the time they were captured (doh!). I just opened up one of the flats there (saved in FITS form), debayered in PI and looked at the histogram transformation window. It looks like this, which I'm guessing is not what it should be..: I did indeed rely on ADU, I have a 14-bit Canon 450D DSLR (unmodified) and I fed a desired ADU level of 8300 to the Ekos software. It took a number of frames, each time calculating the ADU until it settled on an exposure length which was within a tolerance of 500 of the 8300 I specified. ISO was set to 200 and I think exposure length was around 1/7th second. I used a desktop monitor placed on the ground in a darkened room (at night-time), with 'Notepad' application running full screen, and OTA pointing directly at the monitor (no diffuser in between). The OTA meeting the screen was pretty flush with little in the way of a gap on any side. RGGB, Flats were captured in RAW format as FITS files, I think the master flat provided (generated by DSS) is also RAW. The CLS filter was *not* used for any of the flats or light frames on M51 and Rosette. I was just thinking out loud when I wrote the comment so next time I try capture these targets I would try the CLS filter, sorry for confusion. Canon 450D stock without any modifications. F6.3 (SW ED80 DS Pro, with field flattener bringing focal length down to 510mm). Thanks for this suggestion, I guess before trying to figure this out I'll see if the responses to the above might unlock where I've gone wrong!
  15. On my last M51 attempt a week or so back, I saw horrible red/orange gradients in my stacked unprocessed image (lights, flats & bias). I thought it was light pollution and made a mental note to make use of the CLS filter I have in my next attempt. I subsequently stacked some subs I had of the Rosette Nebula area, and again saw the same ugly red/orange gradients in the stacked unprocessed image (lights, flats & bias). What is weird is, the red/orange gradients and pattern appears to be the same in both the M51 and Rosette stacked images. I did an experiment and re-stacked without any flats, and the red/orange gradient was indeed gone - so the issue seems to be something to do with the use of flats. I also looked at some of the 'light frames' and after stretching could not see anything like ugly gradients present. I have attached a sample of what both look like (simple histogram transformation only applied after stacking). Note the same red/orange gradient shaped areas is both images. Has anyone come across this type of issue before where the addition of flats actually makes the image worse, and has a repeated pattern across different targets? Note: my camera was left attached to scope between the targets so the same flats were used for both. But when I look at the master flat, and stretch it I cannot see anything obviously wrong with it. Available here in case anyone wants to have a look (23.7MB): https://we.tl/uZ0F7KJLsr Here is the M51 version without flats:
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