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wimvb

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  1. Looking at your raw stack and single frame, I would guess that the main issue is probably dark current and read noise from the camera. If the camera isn't cooled, it will have a high dark current. While the signal component will be removed by darks, the noise component will be left in each sub. A good Ha filter blocks any light other than Ha (and sky glow at 656 nm), but light frames can be under exposed even at 2 minutes exposure. Sky glow and dark current will increase the background level and noise. Just my kr 2,00
  2. The filters used were Bessel Blue (9 frames), Bessel V (green, 6 frames), and sdss Red (13 frames). There was no Ha (and no hints of Ha regions in the red channel either). A lot of subs had odd shaped stars or were blurry (not surprising, if they use the same autofocuser as in their IR camera: http://telescope.livjm.ac.uk/TelInst/Inst/IOI/ ). My method of searching the archives is either from their gallery (flickr images), or if I find a nice target on the internet, I just search for it in their archives. Most of the time, they don't have it. Or they only have a few exposures. At other times, most exposures are from the old camera (RATCAM), which has a smaller FOV, and a few bad columns. I found one galaxy (ngc 4449) which has quite spectacular Ha areas, and there is enough colour data in the LT archives. But unfortunately only one usable Ha sub in the public archive. When I get better at processing, I may try to combine LT colour data with Hubble Ha data...
  3. That's the easiest fix to this problem.
  4. NGC 4216 is a spiral galaxy belonging to the virgo cluster. Its distance is about 55 Mly. Apparent size: about 8 x 2 arcminutes. The galaxy to the left is one of its satellite galaxies (VCC 65 ?). This galaxy shows a very weak tidal disruption due to its interaction with the larger galaxy. (Barely visible in this image.) Data from the Liverpool Telescope, processed in PixInsight
  5. Great image, Göran. The only comment I would have is the bottom edge which has a colour gradient that I also have seen in my LT images (PixInsights DBE takes care of it). Maybe by the time you can gather your own data again, you'll be spoilt by the quality data you got from the professional telescopes, and you won't want to go back.
  6. Nice widefield from limited time on target. Getting a good orion neb and a good flame/horsehead in the same pic is a remarkable feat, even for an experienced astrophotographer, simple because of the huge dynamic range. I think you've done well here. To get the best out of a pic like this, I would probably create a copy. Process one for the orion neb, and the other for the flame/hh. Then blend as layers in gimp/photoshop. (Wow, can hardly believe I write this, as I use PixInsight exclusively. ) Imaging over several nights isn't dufficult. If you can, leave the rig untouched between night. If you can't/won't, try to leave the mount or tripod untouched. Align the imaging camera with RA and DEC. Expose a single frame for 30 seconds and slew the RA+ during exposure. This will create a straight star trail. Then loosen your camera and turn it. Repeat until the star trail lines up with either the long or short side of the sensor/image. Do this every imaging session. The only thing left is to do an accurate star alignment each session. Use a high power (barlowed) eyepiece for this. Take flat frames after each session. 15 or so is usually enough. It's not absolutely necessary to take flats at the same iso as light frames, as long as you calibrate them correctly. Good luck
  7. In PixInsight, I have used Kayron Mercieca's (lightvortexastronomy.com) recipe with some success. It lets you vary the amount of Ha in red and lum, without affecting the stars. The nbrgb script in PixInsight is tricky, and I've never succeeded with Vicent Peris' method.
  8. Nice image. As you noted, a little overcooked in Ha, but otherwise very good. How was the seminar?
  9. Looks good to me. Challenge: would combining the Liverpool data with you excellent wide field improve the latter in any way?
  10. A. Yes, but you probably only see the effect if the number of subs dropped is about the same as the number kept. Removing two subs out of a stack of 30, hardly makes a difference. But removing those out of a stack of 5 will. B. Yes again, if you dial in the correct kappa value. Adding a bad pixel map in lieu of darks also helps. As will other methods, such as cosmetic correction, which looks at each pixel neighbours in each individual sub, and then replaces it if it deviates more than a certain amount (again in units of standard deviation).
  11. Well worth the effort, it looks great. And +1 for gradientmergemosaic
  12. -- reply removed. Crossing threads --
  13. So, by the end of the summer you'll be turning out Gendler quality hybrids . I will stick to the LT for a while, the archives hold enough information to keep me busy for a few months.
  14. Having 0.3 "/pixel at 2 m aperture and 20 m fl on a mountain top in the middle of the atlantic helps. Great image, Göran. I like the colours.
  15. Looks great. Nice detail in the dust ring.