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wimvb

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About wimvb

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    White Dwarf
  • Birthday 29/07/1963

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    http://wimvberlo.blogspot.se/

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    Sweden (59.47° North)
  1. NGC 6946 The Fireworks Galaxy

    Very nice image already. Darks won't help you get rid of (random) noise. Darks can help remove stuck/hot pixels and amp glow, but not noise. To do that, you need to increase the total integration time, either by increasing the exposure time, or the number of light frames.
  2. Oh No! M51 again! (2018 vs 2017 version)

    Definite progress. The big difference must be PixInsight of course. (... he said, tying his running-shoes)
  3. Cropped and stretched in PixInsight. Mainly noise reduction, stretching and colour saturation. No fancy sharpening, etc. The image needs a lot more data for that.
  4. Leo Triplets

    I downloaded your image (tif), and stretched it in PixInsight (reduced to mono). There's more to pull out of this image near M66. But also a lot of noise with the limited data. And just a hint of the tidal tail. The lighter patch near the top reminds of ifn, but is probably just an artefact.
  5. Leo Triplets

    The kit is running fine. Star shapes look ok and the background is very eve. Just too little data to push it far. Normally I combine the RGB data into one colour image, and process the L seperately. The RGB is processed to get good colour, and the L to get good detail and low noise. After stretching I combine into an LRGB image.
  6. Leo Triplets

    First impressions: noisy. But that's to be expected considering the limited amount of data. No hint of any tidal tail, of course. Does the tif contain the L-data, or just RGB?
  7. Leo Triplets

    My thoughts too. That's why I'm downloading the tiff, and have a look at it. My guess is, that the limited data resulted in a noisy background. A very nice image, though.
  8. M 16 Ha

    It all depends on the subframe exposure time of course. With cooled cmos, you can either use many (hundreds+) short exposures at high gain or fewer (tens+) long exposures at low gain. There is an article/blog post or forum thread on the ZWO site about this. At low gain, you have more dynamic range, but also higher read noise. At high gain you have lower dynamic range and lower read noise. Dynamic range can only be gained by increasing the number of subs, not by increasing the exposure time (at constant camera gain). I believe you need to double the number of subs to gain one stop in range. The final result will also depend on how much light pollution you have. Light pollution introduces sky noise. To compensate for this, you need to increase the total integration time. Again, doubling the integration time for each gain of one in magnitude, I believe. That's why it's impossible to have general recommendation for "point of diminishing returns" or "optimum exposure time". In the end it's a personal judgement (and probably available clear-sky time) which determines when enough is enough. So, when you say you can't see much difference when adding data, you've probably reached your limit. Btw, one way to keep "poor" data in the stack is to give each sub a weight factor. I've started doing this in SubframeSelector in PixInsight, and I have the impression that it increases the final image quality. My weight factor is based on snr, fwhm and eccentricity. It allows me to keep subs that weren't very good, but probably too good to discard.
  9. M 16 Ha

    Yes, but you have a great image already. But unfortunately, dynamic range increases with number of subs, not total integration time. No, never. Add more if you can. More data will also decrease the noise left over after amp glow removal. Amp glow shows itself more at longer sub exposure time. That's why it may be better to shoot more and shorter subs. Just make sure that each sub is well above the read noise floor. If you start to see the read pattern of the camera in each sub, you should increase the exposure time. At least, that's my experience with the ASI174MM.
  10. M 16 Ha

    Lovely. What brand/type Ha filter do you use? The narrower the transmission peak, the better it will be at rejecting light pollution.
  11. Cone and np error shouldn't matter. Just for completeness, here's my procedure, which gives me spot on goto accuracy, even with a barlowed 17 mm eyepiece: - Set up tripod. Aiming north leg to polaris. - Level tripod, using a small builders level - Mount switched off. Setting circles in correct position. Mount in parked position (pointing due north, cw bar down). - Turn on mount. Use synscaninit for location and time input. Make sure north and east/west hemisphere are correct. - 2 star alignment. First star with 25 mm eyepiece, finetune with barlowed 17 mm eyepiece with homemade crosshairs. Also adjust finderscope now. - Align 2nd star with barlowed eyepiece. - Note polar misalignment. - Use synscan polar alignment routine to improve pa. - Repeat 2 star alignment, and check polar alignment error. This procedure should give you a very accurate goto alignment. The pa accuracy after two iterations of polar alignment is good enough for (guided) imaging. Usually, if the pa error is small, even the first alignment star is within the fov of the 17 mm eyepiece. I never slew the mount manually when it's switched on, but only use the synscan hand controller. Hope this helps.
  12. Looks like a nice lightweight package for those who don't need the full power of ekos. Is the page layout compatible with mobile devices, such as tablets or smartphones?
  13. Anyone Imaging with TS UNC or ONTC

    Optical evaluation report of the mirror is included, I believe. My feeling is that these scopes are a serios step up from standard newts. But I'm not sure that the focuser is included. I've looked at the 10" f/4.7, which with Baader Diamond steeltrack, motorfocus and coma corrector, will set you back some 2800 € at least, assuming that focuser is NOT included. Hefty price, but if it has the quality, it may be worth it ...
  14. Flats

    Not on the view maybe, but certainly on the image. Are there dso images around with pinpoint stars from scts and/or other reflectors? Legitimate question, because I haven't looked around. Time to fire up the Google engine, methinks.
  15. Flats

    Dust on the objective shouldn't affect your flats. Dust is moving there all the time anyway. Any surface further away than a flattener/reducer/coma corrector is probably too far from the sensor to matter much. I would take new flats only if a problem shows up. (For a mobile setup it's an entirely different story of course. The bouncing around during assembly and disassembly can knock dust off any surface.)
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