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Found 13 results

  1. Update 16th June: I could not wait to tell people that I was just notified that my image of Omega Centauri will be published as a future NASA's Astronomy Picture of the Day ( APOD ) - my first ever I will update the thread when they publish. ................................. A deep look at Omega Centauri ( NGC 5139 ) This image is an attempt to look deeply into the the Omega Centauri globular cluster by using HDR techniques to record as many faint stars as I can whilst retaining colour and detail in the bright stars, including at the core ... ............. Reprocessed to bring out more faint stars and to produce a smother transition between brightness levels. New version ( 12 June 2017 ): Omega Centauri ( NGC 5129 ) ( please click / tap on image to see lager and sharper ) .......... Old version: Omega Centauri ( NGC 5129 ) ( please click / tap on image to see full size and sharper ) Image details: from www.nova.astrometry.net: Size: 58.6 x 39 arcmins, Centre: 13h 26 min 50.4 sec, -47deg 28' 39.1''. Orientation: up is -89.9 East of North ( ie. E^ N> ). Telescope: Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ). Corrector: ASA 2" Coma Corrector Quattro 1.175x. Effective Focal Length / Aperture : 1410mm f4.7. Mount: Skywatcher AZ Eq6 GT. Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2 . Camera: Nikon D5300 (unmodified) (sensor 23.5 x 15.6mm, 6016x4016 3.9um pixels). No filter Long Exposure noise reduction off Location:. Blue Mountains, Australia. Moderate light pollution ( pale green zone on darksitefinder.com map ). Capture: 9 sets of sub-images with exposure duration for each set doubling ( 1s to 240s ) all at ISO800. Processing:. Calibration: master bias, master flat and no darks. Integration in 9 sets. HDR combination. Pixinsight May 2017
  2. OK, I may just be losing the plot here, but help! Just how does one create a master dark frame and master flat frame for each observing session? I used to be able to do this using Registax, but I now want to use new tools such as AS!2 and maybe even Pixinsight (possibly), but certainly i AS!2's case it needs a master dark/bias/flat frame - not the video sequences that I capture OK, so on each observing session - and in my particular case - its planetary imaging:- i) take lights of object - in this case jupiter - usually 1min video in SER format using Sharpcap ii) Put lenscap on scope and take darks @ same exposure gain settings - again 1 min video in SER format iii) replace cap with light panel and take flats with exposure set to fill ~30% of the histogram - 1 min video in SER format. - I'll investigate bias frames later - just trying to build a workflow for AS!2 at the mo. I'm hoping to build a library of darks at different temperatures for each of my cameras So how do I best convert the SER video files into dark & flat frames for use in AS!2? What software to use and what settings Thanks in advance Neil
  3. Hi! Yesterday I was reading about dark frames vs in camera long exposure noise reduction, and something caught my attention. As far as my (so far little but growing) knowledge goes, the best you can do is to take the calibration frames right after the imaging session. This can be a pain in the A, and as I read yesterday, many takes these frames separately, when there is nothing better to do, like on a cloudy afternoon. This is allright, it's a good idea, you can create different master darks and other master calibration frames on different temperatures (room temp, cold, hot etc), and use these when stacking images from your light sessions according to the temperatures the lights frames were capured at. But. As far as I know, my darks should have the exact same settings and focus that my lights have. If I know I use for an example a prime wide angle lens at F2.8 all the time, with ISO 1600 to capture the milky way, that's okay. But what if something changes? What if I use ISO 3200 for some reason? What about the focus (okay, inifinity, but not exactly the same all the time when manual focusing)? What if I use a zoom lens on different focal lenghts? What about the other calibration frames? It's definitely not impossible to be prepared for every scenario, but when you use lenses instead of telescopes, there are more variations. Extra info, if that matters: I'm using a Nikon D5500, which is "ISO invariant". I'm really curious about your replies, as this could greatly improve my image's quality, if It's possible to take calibration frames this way. Thanks in advance! Árpád
  4. If any of you are interested in a star party in East Suffolk, we have been hosting a Star Party every March and October at Hinton, near Saxmundham, Suffolk at a newly developed Caravan and campsite, Haw Wood Farm, for the last 5 years. It is £12 per pitch per night with electricity hook up (adapter needed) call Dan or Georgina (see link below). Some of you here may know about it; on good nights we have had a SQM reading of 21.75 - it can get dark enough to see the Zodiacal Light! Many local society members meet up: Norwich, Castle Point, North Essex, OASI (Orwell), DASH (local) and Breckland among others and it is generally friendly and welcoming (if we can see you in the dark!). Saturday 14th we run an event: a skytour or talks in the cafe, dependent on weather. Unfortunately, timing clashes with the SGL star party but we're a long way from it. See link for details: http://www.hawwoodfarm.co.uk/things-to-do/events-hawwood/
  5. Hi, I am planning a visit to Ardnamurchan (in Scotland) during the last week in May and the first week in June 2016. Researching the night time darkness it seems to go dark at 23:00 and bright again by 03:30am. But how dark will it be? Should I take my astro gear?, will it be worth the effort given that the Moon will be in the Last Quarter at the time. I camped on Skye in mid June about 6 years ago and it was dim at midnight and seeable again at 02:00am. I could see the outline of the Cullin Hills when I adventured out of the tent! Thanks Adrian
  6. Good morning, I am fairly new to AP (well astronomy generally to be truthful), and am trying to automate the process as much as possible. I currently use SGPro, have an Atik 460EX, EFW2 filter wheel, and AZ-EQ6 mount. My question relates to taking dark frames. Currently I can set up my sequence in SGPro to take all my lights (LRGB), and then I have to pause prior to darks, go out to my rig and cover the scope. I was wondering what the thoughts of the more experienced imagers are with using one of my 9 filter wheel positions as a "dark frame" position, and perhaps covering the aperture with flocking or something similar? Whilst is isn's a real issue going and covering the OTA, I thought that this could make my imaging sessions more automated if it's possible and there aren't related issues that I haven't considered. Many thanks in advance for your advice.
  7. I am hoping someone can assist with an issue I've been having when taking calibration frames on my 300D - only noticed the problem after having the filter removed and to a lesser extent with longer exposure times. I first realised something was wrong when I tried to take the darks indoors with the scope's cap on, and saw that a big part of the frame was illuminated by the lightbulb in the room. I removed the camera from the focuser and tried with just the cap on. Still got light leakage, it seemed from either the viewfinder or the rubber side cover where the sockets are. I have heard of light leakage and covering the viewfinder but with my 300D it hadn't needed it before, so assumed it might have been the filter mod changing the internal parts slightly. I havent really got detailed knowledge of where the light might be reaching the sensor via the openings in the camera casing and haven't heard much on the subject either, so i'm hoping someone might have had the same thing happen or be able to tell from the picture where the light might be coming from. This is a dark from outside with scope cap on, but I think the blue tint is because the sky was getting light near dawn time. I might not have noticed if it was totally dark out and used the darkframe as normal in DSS, but this is now a constant feature in my darks - and less noticeable but present in all my shots. Can anyone help with diagnosing the source of this problem? Maybe as its always in the same place (right hand side, lower right mostly) it might correspond to a certain area of the camera? Any info and all suggestions gratefully appreciated, Regards Aenima
  8. My image of Omega Centauri ( NGC 5139 ) has been published as the NASA APOD for the 11th of July 2017 https://apod.nasa.gov/apod/ap170711.html Link to full size image on NASA site ( warning quite large - 4620 x 3720 ) Link to discussion of image on asterisk.apod.com ( credit apod.nasa.gov ) ( full size image - 4620 x 3720 ) Link to original post for this image back on the 10th of June
  9. In an earlier post I examined the noise in single dark frames over a range of exposure times. My conclusion was that the Nikon D7500 was a lower noise camera than the D5300. This was also backed up by an examination of master bias frames that again strongly favoured the D7500. However ... The first image I attempted to produce with the D7500 exhibited very strong streaks in the noise. I had been in the habit of not using dark subtraction with the D5300 as it has very low thermal pattern noise. Accordingly, I again only used bias and flat frame calibration in the workflow that produced the above images. Whilst the streaks are due to patterns in the noise being spread across the image due to errors in the application of dithering during tracking, it did indicate that the D7500 did have significant thermal pattern noise. I found this surprising because the noise in individual frames ( when looked at in isolation ) seems to be completely random. I thought that perhaps my memory had failed me and maybe the D5300 has the same level of pattern noise but my memory was being tricked. That is, all my recent images with the D5300 were taken at lowish air temperatures ( ~5 deg or so ) whereas the image above was captured on warm nights ( low 20s ) and so maybe the D5300 would be just as bad at higher temperatures. To test this I produced bias corrected master darks for both the D7500 and D5300 from images all taken at around 20 deg or just over. The images below have all been stretched using the same screenTransferFunction applied to the Pixinsight histogram tool. The results are striking ... D5300 master dark ( 47 subs, bias corrected ) - red channel: D7500 master dark ( 281 subs, bias corrected ) - red channel: D5300 master dark 100% centre crop - red channel: D7500 master dark 100% centre crop - red channel: And the histograms of the full size images ( red channels ) ... D5300 master dark ( red channel ) histogram: D7500 master dark ( red channel ) histogram: The Pixinsight statistics tool calculates the following: D5300: mean 2.3, standard deviation 9.3 D7500: mean 7.5, standard deviation 20.8 ------------- Analysis: The images and histograms clearly show that the D7500 has higher pattern noise than the D5300. In particular, from the histograms, 0.1% ( 6,286 ) of D5300 pixels are more than 44 ADU whereas, for the D7500 this figure is 27 times as great at 2.7% ( 141,305 pixels ). Furthermore, the master dark for the D5300 was only produced using 47 images -v- 281 for the D7500 so I would expect that this difference would be even higher with more D5300 frames. On the other hand, whilst not shown in the histograms above, my D5300 does have more 'very hot' pixels than the D7500 ( 579 pixels greater than 400 ADU -v- 10 pixels greater than 400 ADU ). However, these hot pixels are very easily removed via dithering during tracking and sigma clipping when integrating. The very large number of warm pixels however are very difficult to remove as dithering just places different warm pixels on top of each other. I went back and examined the 'random' noise seen in the individual D7500 dark frames ... and yes they do look random when seen individually, however, when flicking between a number of frames it is clear that the 'random' pattern is repeated in each frame! Conclusion: My D7500 has very significant thermal pattern noise, albeit randomly distributed in a fixed pattern. ............ Next steps (?) - I could use in dark subtraction during calibration to reduce the impact of pattern noise - however, as my camera is not cooled and the night's temperatures are constantly changing, any master dark will not closely align to the actual thermal pattern noise and as such dark subtraction may help but will not solve the problem - Using in-camera dark subtraction ( Nikon's long exposure noise reduction feature ) would almost completely remove the pattern noise from each frame. However, due to the extra random noise being introduced by subtracting another noisy dark frame from each light frame, as well as the reduction in total light frames by 2, the resultant images will suffer from higher levels of random noise. So whilst this would be an improvement with respect to the pattern noise, it is not a complete solution. - Third option, sell the D7500 and go back to using the D5300 ...
  10. Below is a comparison between single dark frames taken with the Nikon D7500 and D5300 with exposure durations varying from 1 sec to 240 sec ( my usual main light frame exposure ) all at ISO400. Firstly a graph of the standard deviation of the noise in the dark frames versus exposure time: The standard deviation of the noise is a fairly constant 2 ADU less for the D7500 compared to the D5300 ( pretty much the difference in the read noise between the two ) However, the difference is not just in absolute terms but also in the quality of the noise ... Below are the dark frames - ranging from 240 sec exposures at the top to 1 sec at the bottom: D7500 D5300 The D5300 dark frames clearly show the pattern in the read noise ( banding down the bottom ) and also have far more chrominance noise compared to the D7500. At 240 seconds ( the main exposure I have been using ) the difference is starkly different; the D7500 produces images with much lower noise that is significantly more even and random and hence more likely to be reduced during integration.
  11. The Rosette Nebula and Cluster ( NGC 2237 and 2244 ) in the constellation Monoceros edit: updated 30th Dec with improved colour balance and slightly increased brightness ... ...... original: ( please click / tap on image to see larger and sharper ) Still a work-in-progress really... with only 10 x 4min exposures for the main 'lights' before the clouds came over. I will try to add some more data when the moon has gone I am still experimenting with how to get the best out of the D7500. With the very warm nights ( low to mid 20s all night ) the 'warm pixels' are very noticeable so I reverted to my old practice of in-camera dark subtraction. This worked quite well and produced a nice smooth noise floor in the integrated images - albeit at the expense of more exposures. ................. Identification: The Rosette Nebula ( NGC 2237 ) is a large, circular emission nebula in the constellation Monoceros. It surrounds a cluster of hot, young stars known as the Rosette Cluster ( NGC 2244 ). ( SkySafari ) NGC 2237, 2244 Caldwell 49, 50 North is up. .................. Capture Details: Telescope: Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ). Corrector: ASA 2" Coma Corrector Quattro 1.175x. Effective Focal Length / Aperture : 1400mm f4.7 Mount: Skywatcher EQ8 Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2 Camera: Nikon D7500 (unmodified) (sensor 23.5 x 15.7mm, 5568x3712 @ 4.196um pixels) Location: Blue Mountains, Australia Moderate light pollution ( pale green zone on darksitefinder.com map ) Capture ( 23 Dec 2017 ) 9 sets of sub-images with exposure duration for each set doubling ( 1s to 240s ) all at ISO400. 10 x 240s + 5 each @ 1s to 120s imaged ~ +/- 1.5hrs either side of meridian maximum altitude ~ 51.3 deg above north horizon Processing ( Pixinsight ) Calibration: master bias, master flat and in-camera dark subtraction Integration in 9 sets HDR combination Image Plate Solution =================================== Resolution ........ 0.633 arcsec/px ( full size image ) Rotation .......... 0.181 deg Focal ............. 1367.90 mm Pixel size ........ 4.20 um Field of view ..... 58' 59.4" x 39' 15.0" Image center ...... RA: 06 31 55.638 Dec: +04 56 30.84 ===================================
  12. The Great Barred Spiral Galaxy ( NGC 1365 ) in the constellation Fornax edit: new version with new long exposure data ( 52 x 240sec ) and better dark subtraction / dithering to remove streaks in the noise and amp glow. This also allowed for a greater stretch revealing more faint data in the galaxy and small faint fuzzies in the image .. The Great Barred Spiral Galaxy ( NGC 1365 ) in Fornax ( please click / tap to see larger ) and below I have added a 100% crop of new version: ........ original image: NGC 1365 ( please click / tap on image to see larger ) ............... The Great Barred Spiral Galaxy ( NGC 1365 ) in the Constellation Fornax Below the equator, not seen from much of the Northern hemisphere, NGC 1365 passes very nearly directly overhead an observer situated near Cape Town, as Sir John Herschel was in November of 1837, or near Sydney, as I was, almost exactly 180 years later, when I photographed this “remarkable nebula” that is numbered 2552 in his book of observations from the Cape. Not called a “nebula” now, of course, this striking object is one of the nearest and most studied examples of a barred spiral ( SB ) galaxy that also has an active galactic nuclei resulting in its designation as a Seyfert galaxy. At around 60 M light years from Earth, NGC 1365 is still seen to occupy a relatively large area ( 12 by 6 arc minutes ) due to its great size; at some 200,000 light years or so across, NGC 1365 is nearly twice as wide as the Milky Way and considerably wider than both the Sculptor and Andromeda galaxies. This High Dynamic Range ( HDR ) image is built up from multiple exposures ranging from 4 to 120 seconds with the aim of capturing the faint detail in the spiral arms of the galaxy whilst also retaining colour in the brightest star ( the orange-red 7th magnitude giant, HD 22425 ). Also, scattered throughout the image, and somewhat more difficult to see, are numerous and far more distant galaxies with apparent magnitudes of 16 to 18 or greater. Mike O'Day ................. Identification: The Great Barred Spiral Galaxy New General Catalogue - NGC 1365 General Catalogue - GC 731 John Herschel ( Cape of Good Hope ) # 2552 - Nov 28, 29 1837 Principal Galaxy Catlogue - PCG 13179 ESO 358-17 IRAS 03317-3618 RA (2000.0) 3h 33m 37.2 s DEC (2000.0) -36 deg 8' 36.5" 10th magnitude Seyfert-type galaxy in the Fornaux cluster of galaxies 200 Kly diameter 60 Mly distance .................. Capture Details: Telescope: Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ). Corrector: ASA 2" Coma Corrector Quattro 1.175x. Effective Focal Length / Aperture : 1400mm f4.7 Mount: Skywatcher EQ Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2 Camera: Nikon D7500 (unmodified) (sensor 23.5 x 15.7mm, 5568x3712 @ 4.196um pixels) Location: Blue Mountains, Australia Moderate light pollution ( pale green zone on darksitefinder.com map ) Capture ( 22 Nov 2017 ) 6 sets of sub-images with exposure duration for each set doubling ( 4s to 120s ) all at ISO400. 70 x 120s + 5 each @ 4s to 60s total around 2.5hrs Processing ( Pixinsight ) Calibration: master bias, master flat and no darks Integration in 6 sets HDR combination Image - Plate Solution ========================================== Resolution ........ 1.328 arcsec/px Rotation .......... -0.008 deg ( North is up ) Field of view ..... 58' 8.6" x 38' 47.5" Image center ...... RA: 03 33 41.182 Dec: -36 07 46.71 ==========================================
  13. When taking Dark frames, I think I'm right in saying that a) they are taken at the same exposure settings as the lights, b ) at the same temperature as the lights. In which case, with the ASI1600, can i just do this indoors (not at the scope), just be capping the end of the camera, setting the necessary temperature, wait for the camera to cool and then take my darks, all from the comfort of my armchair? And thus by setting different temperatures (say -25, -20, -15) build up a library of darks at different exposures (1sec, 2s, 4s, etc etc) and then build myself a set of master darks? Thanks in advance Neil
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