During first light and the first several nights I took the telescope our for successful testing, a couple of issues came up. Huge amounts of unwanted stray light were streaming into the telescope from around the primary mirror. And I needed a place to put my eyepieces and coma corrector while swapping them where they would be safe from getting dropped onto the ground, or worse yet, pavement. Therefore I set out to address both shortcomings with solutions that were simple but effective use of materials available.
The first issue was corrected with a light baffle made from leftover Ripstop Nylon fabric. As you can see from the photo, air can still flow around the mirror easily and I can reach the collimation bolts to collimate the telescope after I set it up. The light baffle blocks stray light quite well and neither disturbs the balance nor does it interfere with the telescope's motion in altitude. It's held in place with several tabs of Velcro and can be installed or removed at any time. The improvement in contrast was noticeable now that there is no longer a torrent of stray light coming in around the primary mirror and getting into my eyes.
The eyepiece holder was made from two pieces of three-inch wide steel flat-bar one eighth or an inch thick, or about 7.5 centimeters by three millimeters in metric measurements. After carefully laying on the spacing of the holes on a sheet of paper, I marked the metal at the correct spots with a hammer and center punch. Then I drilled the holes with my half inch power drill and the appropriate hole saws, which were 2-inch (50mm) and 1 1/4-inch (32mm). I used some oil to keep the hole saws from overheating then dulling as I drilled out the holes, which were smoothed with a drum sander and a file.. In the other piece I drilled two holes for the mounting bolts. Then I sanded the metal until it was bright and shiny, and clamped the pieces to a piece of steel angle iron which served as a jig so I can tack weld them together. Once tacked and the squareness was verified,. I then welded the seam along the outside corner with my welding machine using MIG welding wire and a mixture of 75 percent argon and 25 percent carbon dioxide for shielding gas.
Once the welding was done, I cleaned up the weld and primed it with a metal primer. Then I applied three coats of glossy black paint. To mount it to the mirror box, I used threaded inserts coated with epoxy glue, then bolted the eyepiece rack in place. Now I can put an eyepiece or coma corrector lens there, and not worry about it falling to the ground and getting damaged. Good eyepieces cost a lot of money, and this is a simple way to keep them safe from harm and at the ready too.
Thursday, March 3, 2011
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.