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michael.h.f.wilkinson

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About michael.h.f.wilkinson

  • Rank
    Neutron Star
  • Birthday 21/01/62

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  • Website URL
    http://www.cs.rug.nl/~michael

Profile Information

  • Gender
    Male
  • Interests
    Astronomy, computer science, photography, wildlife, cookery, life the universe and everything
  • Location
    Groningen, The Netherlands
  1. Solar Sunspot Group 15th Nov, 18th Nov 2017

    Nice shots. A pity it seems to be shrinking
  2. NGC 1333

    Lovely result
  3. Solar Viewing and H-Alpha filter?

    Your run of the mill 1.25" H-alpha filter is intended for deep sky work and has a bandpass of between 3 and 35 nm wide. A solar H-alpha filter is an entirely different beast, and has a bandwidth of 0.03 - 0.1 nm. These are far more expensive. One of the cheaper options is the Daystar Quark, which can be inserted into smaller refractors, turning them into H-alpha solar scopes. Deep sky H-alpha filters are not suitable for solar work and are positively dangerous if used without some VERY strong other filters to prevent dangerous light levels to reach the camera or (worse) your eyes.
  4. 1% illuminated moon + activity in foreground

    Nice one. Very atmospheric
  5. 80mm frac opinions

    I think my APM 80mm F/6 has the same front element as the ES triplet. Very pleased with that scope
  6. M45 The Pleiades

    Very nice indeed!
  7. M42 + Running man

    Amazing stuff!
  8. Imaging in the Netherlands

    Don't get me started ...
  9. Yesterday morning was sunny, and I finally managed to get some shots of the sun in Ca-K and WL with the 80mm APM. WL, grey scale: WL, pseudo colour: Ca-K, grey scale: Ca-K, pseudo colour: Ca-K, part inverted: Ca-K, part inverted + pseudo colour: Seeing was poor, and the skies hazy, so I was pleased that I got detail at all. To round things off, I did a quick test to see whether my ASI178MM would come to focus with the old LS35THa I used to have, which is now used by the Kapteyn Astronomical Institute for outreach (and possibly teaching). The idea is for the Kapteyn Institute to get an ASI178MM to let students do some solar imaging for practicals, and perhaps for outreach as well. I just took a few shots, no flats, no clocking to even out the banding. Not great, therefore, but the scope did come to focus. Not bad for just 100 frames out of 1000 stacked.
  10. Sun-17-11-17

    Lovely images and animation
  11. Or Sinterklaas here in the Netherlands
  12. NGC891 at 1015mm FL

    Nice one. Very vibrant colour
  13. Tried the old Contax mounted Carl Zeiss Tele-Tessar 3.5 200 mm on the EOS 700D with CLS clip filter to see if I could get focus, and of course some usable data. M45 came first, with 20 lights and 10 darks, after that I took some 16 lights of M31, and then the camera battery died, so I packed it in. All exposures 120s at 1600 ISO. Did a quick stack in DSS. Not content with the (lack of) colour. Will have a better bash tomorrow. Clearly, I can come to focus in this configuration. More data are needed for better results, no doubt, but the lens itself seems to be doing a good job, right to the corners
  14. Andromeda DSLR and focal reducer

    If you want the same number of photons per pixel, which will determine the signal-to-noise ratio in a photon-noise-limited system, reducing the focal ratio gives a similar result as extending exposure time. If you want to keep the image scale and exposure time the same, then you need to increase aperture to reduce the focal ratio (expensive), otherwise a focal reducer is needed. If the system is not photon-noise limited, but instead is limited by dark current, you need to lift the signal above the dark current noise (subtracting darks only removes the average value per pixel, not the random fluctuations), and concentrating more light onto each pixel for a given exposure time is needed, where again a fast focal ratio is needed.
  15. Andromeda DSLR and focal reducer

    First try I did at Andromeda, I used a focal reducer to F/4.8 on my F/6 scope, and got some detail in 60s and 120s subs. The ED-80 is F/7.5, so a factor of 2.44 more exposure would be needed to get the same result without a focal reducer.
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