Thursday, March 3, 2011

Shroud made



As I had mentioned in a previous post, the telescope works very well but stray light is an incredibly annoying problem when I use the telescope at home. Thus a shroud is required and for the past two weeks I was hard at work sewing one. To make the shroud I purchased four yards of black Ripstop Nylon fabric, which is thin but very strong material that resists sunlight and is unaffected by moisture. It resists tearing and is machine washable, but it also allows air to pass through as it blocks stray light.

I started with pinning two pieces of  Ripstop together larger than the truss-tube and pinning them together along the tube's length. Because I  had a conical tube, I ended up using a long narrow piece to join the rest of the shroud together.  Then once I pinned the seams along the length, I triple sewed them along the length with a sewing machine. Along the top I made a hem with a draw cord and sliders, along the bottom I made two reinforced slits to accomodate the altitude bearing and a wider hem to accept metal gromets. Because the shroud came out a little short, I made three flaps for the top and sides of the mirror box to help seal out stray light. A draw cord and another pair of sliders allows the shroud to be tightened around the top of the mirror box.

Now that the shroud has been finished, the next step is to make a light baffle for the rear of the mirror box. An enourmous amount of stray light streams in around the primary mirror, a big problem in a built up area. There  is still a problem with stray light coming in to the focuser directly as well, requiring a shade for the upper cage to block that source of stray light. Before finishing the shroud, I used it when I observed a number of planetary nebulae and globular clusters last weekend. It kept the optics dew free and made a major difference for the better in the views too. All of the globular clusters I observed looked like a huge pile of shattered glass glinting in the sunlight. They were M-3, M-5, M-13, M-92, M-68, M-80, M-4, M-53 and M-10. I also observed the galaxies M-65, M-66 in Leo and M-104 in Virgo, which showed it's famous hat like profile. The planetary nebulae NGC-6210  in Hercules was an amazing blue disk that showed an oval outline and patchiness throughout, with the central star glimering in the center. Another planetary nebula I located was NGC-4361 in Corvus the Crow. Saturn was the show stopper, I clearly spotted both the Cassini and Encke divisions in the rings, which looked three dimenensional at 400X. Last but not least, I looked at the waning crescent moon, which took up most of the field of view at 95X. It was of course very bright and very impressive. Cloudy weather and work considerations has prevented me so far from taking the telescope to a dark area, but hopefully the end of this month will be that opportunity since clouds and rain are going to be here this weekend again.

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