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Roel

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Everything posted by Roel

  1. While designing a ultra portable travel dobsonian I encountered the problem of applying a sufficient primary mirror edge support within the extremely limited amount of space available. I wanted something as simple as possible, which would always support the mirror in the center of gravity. I came up with the following solution: First I determined the center of gravity with this great online tool: http://www.cruxis.co...ecalculator.htm I glued two narrow strips of Formica onto the edge of the mirror, exactly in its center of gravity. The center of both strips were placed 90 degrees ap
  2. Two weeks ago I went on an astronomy trip to La Palma with a few fellow amateur astronomers. We visited the huge GTC and the Mercator telescope on top of the island. We got a guided tour at both telescopes and as a very special bonus the staff of the Mercator allowed us to spend the night at the telescope building and observe with our own telescopes right next to the dome. Wandering around the observatories at night is something which is normally strictly forbidden, so you can imagine it turned out to be one of the most memorable observing nights we ever had.The best thing was the weather bei
  3. Almost every last week's night was cloudy, or even rainy... But on the evening of August 13 the sky cleared big time, and a wonderfully transparent atmosphere showed the Milky May, even while the moon was still up. The Andomeda Galaxy and the Double cluster were easy naked eye objects, and an occasional Perseid flew in front of it all. When the Moon set, the Milky Way quikly turned brighter and I started sketching all Perseids I saw on a pre-drawn pastel sketch (white pastel on blue paper) with only the brightest stars of the eastern sky and a faint Milky Way. I drew the trees on site wit
  4. Yesterday I scanned the two remaining sketches of the Mercury transit. These are from the ingress of Mercury as seen through my 60mm "Solarex" h-alpha telescope. The images are kept mirror reversed so they represent the view through the eyepieces. A funny thing I observed during ingress was the silhouet of the inky black dot of Mercury against what I would normally call "black space" next to the prominence. It might habe been some visual mindtrick, an illusion (I didn't noticed it untill Mercury already made a very big dent), but I really thought I could see the dot as a whole in front of a di
  5. Yesterday's transit of Mercury in front of the Sun was almost entirely visible from the Netherlands. The transit started around noon in a perfecly clear blue sky and it stayed that way untill around 6pm, when high clouds slowly came in from the south. Unfortunately I missed the end of the event, but nonetheless I was able to watch everything non stop for hours. And it was absolutely wonderful! It started with one of the greatest views I ever saw through my 60mm h-Alpha telescope: the tiny planet's black disk just grazing the side of a prominence. While the dot was just making a dent in de
  6. Last night I made a short timelapse movie of the assembly of this telescope. I don't know how to embed a movie clip, so here's the direct link: https://vimeo.com/165319385
  7. Yesterday I cut all of the truss tubes in half and put M6 threaded plugs inside. A threaded rod in one of the ends, and now I have a bundle of 17" in lenght to transport instead of 34". This can easily be strapped to the side of my backpack (in which I plan to transport the whole "observatory" including telescope, eyepieces, folding seat, atlas and sketching material) . I also wrapped them with heat shrink tubes. Paint tends to scratch very quickly, and heat shrink is not als cold to the touch. It adds a little bit of extra weight though, but the scopes is still perfectly balanc
  8. Ouch! That clip hurt my eyes... That's a bit more than "heavy shaking"... Ok, carry-on it is. About things touching the mirror surface: most commercial mirror cells use rubber clips or felt lined metal of some sort to fixate the mirror. I have never seen any damage to the coating because of these clips, and the "amount of touching" is pretty much the same in my scope. (I'm talking about aluminized / quartz coated mirrors by the way, but I believe that's what you meant also with "silvered".)
  9. @Derek: The mirror is protected by a thin plywood lid, which has a bit of an "overhang" on the edges to prevent the mirror from sliding sideways. It is a snug fit between the mirror edge and the truss clamps. The lid lies directly on the mirror so the underside has a layer of soft flocking material. (The mirror surface is of course curved, so the lid actually only touches the outer edge). Everything fits very tighly together when the box is closed, so there is absolutely nothing moving or rattling inside. I can even shake it really wildly and nothing moves. Although it's designed for airline c
  10. The telescope is finished! Pictures of the closed box: The opened box:
  11. Thanks for the kind words! This weekend I cut the last pieces of plywood, these are for the rocker box/transport box.
  12. Today I've cut the trusse to a few centimeters longer than calculated, and made the upper connectors (I'll post pictures of those in detail when finished). And I couldn't help myself making a quick layout on the floor, to see how the OTA will look when assembled.
  13. From the local hardware store, and from the garbage container at my work.... Top view: Bottom view. Note the pointed tips of the (M4) collimation bolts, to prevent them from "skating" around while collimating. The spider vanes' tips are folded and hammered from above into a narrow slot in the hub. Very rigid connection! The metal strips are packaging material, it is uses to strap heavyweight materials (like tiles and pavement) onto pallets. I pulled these from a garbage container at a construction site. Thickness about 0.5 mm.
  14. This morning I finished the spider. It's a very simple three vane systeem with the well known push/pull collimation. The vanes are very thin, which can be seen in the picture below. I placed the focuser a little bit more to the "top" instead of the common 45 degrees angle: It is a small telescope and while observing low above the horizon you'll get a much more comfortable viewing position.
  15. It's going to be the classic three push bolts/ one pull bolt system. Supperted by a three vane spider. Just glue.... A Leica zoom is WAY over budget, and I'm very happy with the performance of my LVW's in fast telescopes (like my 14" f/4). They are also quite parfocal which means the travel of the focus can be very limited. By the way, I finished the altitude bearings:
  16. This is the primary mirror box/cell. Because of the thickness of the mirror a three point support is sufficient according to PLOP - which makes things definitely easier to build. The mirror simply rests on the tips of three nylon bolts. Just turn these bolts to collimate. The box is simply a plywood plate with the truss connectors at the corners. Although the birch plywood is rigid enough for a very stiff stucture, I kept two corners attached to eachother for extra rigidity. The two altitute bearings will be bolted to the sides and will also add extra stiffness. (I already applied so
  17. This autumn I will be staying on the island of La Palma for a week of deep sky observing together with some of my observing buddy's. But what kind of telescope should I bring along? After lots of thoughts and some rough sketching I came up with what for me would be the ultimate travel scope... Last week I started building a 10" truss telescope that would easily fit inside a normal backpack and be light enough to be carried to desolate mountain peaks or other exotic observing locations. I have also considered to make it a 12" but in the end I chose a 10" over a 12", because the latter woul
  18. For the third night in a row (believe me, in the Netherlands that's a weather anomaly) my backyard got a nice clear sky, so again I took my old Russian Novosibirsk TAL150P reflector outside for a moon sketch. It was pretty cold above a thin layer of snow, but that only added to this Siberian-style observing session. I picked Aristillus and Autolycus to draw with a white pastel pencil on black paper. The central "rubble" of Aristillus was perticularly pretty to observe - I counted seven peaks - but the tiny crater on the rim of Autolycus was also a nice feature that was visible. For a larger ve
  19. Roel

    Rimae Hyginus

    Last night I made a sketch of the beautiful Rimae Hyginus. Hyginus itself appears to be an impact crater at first sight, but closer inspection reveals it doesn't have a raised wall, it's just a hole in the surface. It's an extict volcano, with collapsed lava tubes forming the famous rille system. At high magnifications hints of small craters inside the canyons are visible, another sign of a volcanic origin. I made the sketch with a white pastel on black paper. It is the original sketch made behind the eyepiece.
  20. After weeks, no months of mostly cloudy skies, last monday morning I finally got the chance to see the elusive Catalina myself. Well before sunrise I put my little 200mm f/4 Dobsonian in the backyard (sqm 20.0 skies) to make a quick sketch of this wonderful comet. Both tails were visible, although not as bright as images suggest. I was a great sight! It's not that often a two-tailed comet flies by (not to mention how well it is placed high in the northern sky).
  21. After more than 10 years of observing with various telescopes I had never observed Pluto in my life! So on my summer observing trip to la Palma (where Sagittarius is much higher in the sky) I took a detailed finder chart with me and started looking for the mysterious dwarf planet that just weeks before was visited by New Horizons. With my 14" Dobson I made a sketch of the surrounding star field the first night, plotting the tiny speck of light on three nights that following week. Later I used the scanned sketch to make a GIF animation, which I think is the best way to show the movement of Plu
  22. Almost invisible at my northern (52deg) latitude, the splendor of the magnificent Sculptor Galaxy is always hidden below the horizon or behind murky low haze. On my observing trip to La Palma (28deg) however, I almost tumbled into the Caldera when I first saw the Galaxy well above the horizon amongst a starry sky as beautiful a sky can be. It turned out to be the highlight of the whole trip. Simply amazing! I observed this huge galaxy for almost a hour, trying to pick out every visible swirl. It was bright, with very evenly distributed light patches throughout the galaxy, but still the contras
  23. In August 2015 I travelled to the wonderful Canary island of La Palma to observe the night sky with my home-built telescope. Meanwhile, I made a series of time-lapse sequences in which I tried to capture the splendor of the incredible La Palma night sky. I am mostly a visual observer and not particularly a astophotographer, and besides some test sequences shot at home, this is my first attempt to shoot and edit a time-lapse movie like this. For most of the scenes I used some sort of motorized tracking platform - a Skywatcher Star Adventurer mount or a home-built timelape slider. In some of the
  24. Sorry, forgot to attach the image!
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