Tuesday, March 15, 2011

Latest improvements

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.

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