University Lowbrow Astronomers

The Odyssey 2 Continues: Return of the Secondary Mirror.

by Jack Brisbin
Printed in Reflections: April, 2008.

At the February meeting, we discussed what to do with the secondary mirror. However, before we could do anything I had to separate the secondary mirror from the metal bracket it was attached to. The dimensions of the secondary mirror are as follows: Width 4.25 inches, Length 6 5/16 inches, Weight 1 pound and 8.8 ounces, and Thickness is 1 inch. There are some other pictures of the secondary mirror in the February 2008 newsletter. (See “The Odyssey 2 Continues” by Jack Brisbin, February, 2008).

The secondary mirror is glued to the back of the metal bracket. It looks like the back of the mirror has a cloth membrane glued to it and the metal bracket has foam tape that has adhesive on both sides.

Secondary Mirror/Bracket in Vice

Figure 1, explains it all. I put the secondary mirror/bracket in a vise. I inserted a fine tooth hacksaw blade in between the cloth membrane and the foam tape and proceeded to cut through. It took a few minutes but the hacksaw worked quite well and that was not the hard or time-consuming part. Dissolving the cloth membrane and adhesive from the back of the secondary mirror was a larger issue.

Back of Secondary and Metal Bracket

Looking at figure 2, you will see a cloth membrane on the back of the secondary mirror and three strips of foam tape on the back of the metal bracket. To dissolve the glue I filled a small aluminum pan with about a quarter inch of acetone and laid the secondary, glue side down in the acetone for about 10 minutes to soften it up. I used a small metal bristle style brush to abrade the back of the secondary and separate the cloth from the mirror. Once it started to separate around the edges I put the mirror back in the acetone solution to soak for about 5 minutes. I took the secondary out of the solution and brushed the back of the secondary and the membrane peeled off. I used a rag with some acetone on it to wipe off the glue and any residue left on the back of the secondary mirror.

Back of Secondary after Cleaning

Figure 3 shows the back of the secondary with the membrane and glue all cleaned off. You will notice at the top of the secondary there is a small chip that was painted over by Coulter. You don’t notice it glued to the metal bracket. The chip has been there since the telescope was made so it presents no problem. I still have the metal bracket and the large single vane secondary holder. Since it is the Club’s Secondary Mirror, what do we do with it?

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This page originally appeared in Reflections of the University Lowbrow Astronomers (the club newsletter).
This page revised Sunday, March 9, 2014 4:30 PM.
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