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Roel last won the day on December 8 2013

Roel had the most liked content!

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About Roel

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    Star Forming

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    Deventer, The Netherlands
  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 apart. Next I glued two vertical strips of Teflon directly onto the inside of the primary mirror box: And this is what it looks like with the mirror installed: The mirror is now supported only at the point were the Teflon and Formica meet. Because the strip of Formica is placed at the COG and the Telfon strips are 90 degrees apart, the mirror is always supported correctly, even when sliding up and down during collimation. The required space is even less than with a cable sling. I have used this idea on several telescopes now and it works great! The fricton between the two materials is very low without "stiction" so collimating is very smooth, even with the OTA pointed relatively low. By the way, this is the complete telescope, a 350mm (14") f/4:
  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 being absolutely perfect. Almost no wind at all (a rare thing at that altitude) and a crispy clear sky. The gegenschein for example, was very prominent. We observed from dusk till dawn (duh!) with our telescopes. It was nothing less than magical to be under such an ocean of stars, with the sound of the rotating dome of the Mercator - and the humming of the nearby Liverpool Telescope's motordrives - right next to us. Heavenly! The first sketch I made that night was of the beautiful dark nebula B86, which is flanked by the nice bright open cluster NGC 6520 - roughly the same size as the Barnard dust cloud. Just like the clump of stars is plucked out of the Milky Way, put aside, leaving a dark hole. The darker the sky, the better the object is a rule especially true for these kind of objects. The Milky Way background was a bright haze, the cluster a bag of jewels, and the nebula inky black. I mean really really black. "Ink Spot Nebula" is indeed the best name for this great patch of darkness. I used a background of smeared-out graphite, then I drew the stars with a grey graphite pencil. The Barnard cloud was then "drawn" with an eraser. The faintest stars were added last. They are not all placed correctly (which would be near impossible) but they do give the best impressoin of the view through the eyepiece - hundreds of tiny stars amidst a cloud of unresolved Milky Way stars. The image is the original field sketch - besides inverting and the yellowish color of some stars the sketch is unaltered.
  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 with a felt tip pen. The meteors were then added with a pastel pencil. Some of the brightest meteors showed a very distinctive green hue, and most left misty streaks behind for a few seconds. The green hue was added "on the feel", because the colour of the pencil was invisible in red light. Fortunately it turned out great! Afterwards I added a lot of faint stars to complete the drawing. (of course the faint star are not accurately placed, but it makes the sky looking more like it really was: filled with countless points of light). Close-up: Larger 1500px versions can be found here: http://www.roelblog.nl/2016/08/perseiden-2016-super/
  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 dim reddish background hue. Maybe some faint halo of the prominence, or even of the chromosphere? Anyway, the view was stunning! Mercury was a lot bigger than I had expected. Before the ingress I was was waiting for just a tiny speck to enter the solar disk, but when a clearly defined round dent appeared, I couldn't supress a "yes, yes, yes, yes"! Although a lot smaller, it reminded me of the Venus transit a bit more than I expected. Sketches are made behind the eyepiece with a white pastel pencil and a black pen on black paper. Color is digitally added by changing the color balance of the sketch. No further alterations .
  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 solar disk, the rest of the planet's dark side was ghostly visible against the background of a very dim "halo" next to the brightest part of the prominence. An incredible sight! When the transit proceeded I started making a pastel sketch of the entire Sun's disk. Some small prominences were visible around the edge, and the northern half of the Sun was decorated whith nice filament and mildly active regions. After one hour I finished the drawing with the tiny and inky black dot of Mercury. I photographed the sketch the same evening, and used Photoshop to give it an orange hue and to correct the mirror reversed image. No further alterations were made. And this is a close-up of the same drawing, to show the tiny planet's dot more clearly:
  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 balanced with the same bungee cord as before.
  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 carry-on restrictions, I would have no problem with puting it inside the check-in suitcase (of course protected from hard shocks by putting some clothes around it) In transport mode the collimation bolts are turned al the way out so the bottom of the mirror rests on the soft felt pads you see on one of the pictures - so no dangerous stresses on the glass. One has to do some pretty crazy things to damage what's inside!
  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.
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