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About Ruud

  • Rank
    Free-Floating Planet

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  • Gender
  • Interests
    Thank you for visiting my profile. Besides astronomy, I take an interest in photography, skepticism, science, maths, podcasts, radio and cycling. I teach mathematics.
  • Location
    the Netherlands
  1. Ruud

    What Diagonal?..

    Dielectric mirrors do not use reflective materials. No aluminium, silver or whatever. They rely on constructive interference from many thin, transparent layers. Fifty or more transparent layers. Reflectivity is typically 99%.
  2. Ruud

    What Diagonal?..

    I have two 2" diagonals, a TeleVue a William Optics, and I can't see the difference. I also have two 1.25" ones by William Optics, and they seem just as fine. Dielectric diagonals have my preference. You really don't have to worry about cleaning: there is no delicate coating that you have to be careful with. A dielectric layer is very hard, scratch resistant and will not dull after repeated cleaning.
  3. Ruud

    Locking focus on my telescope

    The knob is probably to prevent focus creep, but everyone else already said that. I have a question: I've been looking at this telescope. I thought I'd buy it for birding and as a super portable visual scope, as well as a bit of photography. Do you think this telescope would be a good choice for that?
  4. Ruud


    Feb 2018 was a good month for the seeing! Maybe you'll have better conditions soon, and a chance to photograph the oval in the same position as last year. That would be nice. Great work! Thanks.
  5. When you view the Moon through a telescope, the biggest risk you run is that you lose your dark adaptation. The Moon is as bright as a stretch of asphalt on a sunny day. Watching it with any telescope won't hurt you. If the Moon's brightness bothers you, three things will reduce it: 1) use a higher magnification, 2) use a Moon filter or 3) use sunglasses. A filter is the least convenient because you screw it on the end of the eyepiece. I use method 1.
  6. Ruud

    Starting the season!

    It's great. I guess the seeing made it all soft and fluffy, and gave it these beautiful, gentle colours. A lovely , dreamy Jupiter. Thanks!
  7. Cool! It's very hot of course, the Sun is, but it's a dry heat. Thanks. Great work!
  8. Achim, this is amazing! Twice so because yesterday evening I decided to make a hard bristle/camel hair painting on burlap of exactly the same region. As a starting point I used a 4x enlarged computer generated image (#1150 which I found through SVS home) and Corel painter essentials for the "artwork". detail The burlap is from photoshop. The scene is for 22:00 CET for 17 Feb 2019. I'd so much like to be able to sketch at your level. At the telescope. That would be so gratifying!
  9. Ruud

    R.I.P Opportunity

    My batteries are dying, and it is getting dark
  10. It has a nature of its own. Different, interesting and good. Is this charcoal that you make yourself? Thanks
  11. A coma correcting eyepiece would introduce a kind of "anti-coma" to correct for the coma produced by the objective. This makes coma correcting eyepieces unusable on coma free telescopes. So there are no coma correcting eyepieces on the market. Coma is a property of the objective, not of the eyepiece. Eyepieces are almost always coma free. A good eyepiece shows the focal plane of the objective faithfully, including the coma that is there. Separate coma correctors exist for Newtonians. You adjust them per eyepiece. I'm not sure why but I think this is needed because eyepieces usually aren't parfocal and the distances between the field stop of the eyepiece and the corrector matters. It must be something like this. --- Fast telescopes: I have an f/5 which is fast enough to see the difference between for instance a Hyperion (not so good) and a Morpheus or Delos (both very good). Some designs just don't work very well on fast telescopes and produces unsharp off axis views. The same eyepieces may work very well on slow telescopes.
  12. Ruud

    Lunar craters Aristoteles and Eudoxus, Feb 11th

    It is a wonderful sketch, Achim. Thank you!
  13. Ruud

    An early Leo Triplet - CCD + DSLR

    It's a wonderful image. Beautiful pastel colours on the galaxies, fine details in the disks, and the enormous wispy streamer coming off the Hamburger galaxy is recorded wonderfully well. Even the noise looks great, minimal and regular like a very fine film grain. Thanks for a masterly portrait of the triplets!

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