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    Re: freiberger mirrors (surface coated) repair/replace options
    From: Bill Morris
    Date: 2010 Apr 4, 13:15 -0700

    For re-silvering, or rather, re-aluminising, first port of call might be your local astronomical society, as nearly all amateur astronomical telescope mirrors are now aluminised and they would know who does it locally.

    You could try your friendly local glazier and ask him to cut second surface mirrors out of 4 mm float glass, which is quite flat enough for the purpose. There are two disadvantages to this: light loss due to reflection off the first surface(depends on angle of incidence) and on passing twice through the glass; and displacing the apparent position of the reflective surface backwards makes it slightly more difficult to correct perpendicularity error of the index mirror. The first is of little importance and the second largely theoretical and can be overcome by using sighting vanes, dominoes, hexagon nuts, precision cylinders or what-have-you at zero and 120 degrees, as shown in the attachment. These bring the line of sight up to the approximate axis of the telescope.

    On removing and replacing the clips, it is helful to sit at a table, wearing an apron with its skirt clipped to the table. That way, the clips and their tiny screws are less likely to escape on to the floor. When replacing, make sure the adjusting screws are slackened off. Put the screw through the clip and position it over the corner of the mirror/bracket. Push down on the coiled bit at about 45 degrees and after a little practice and a few false starts, you will be able to start the screw in its hole. It's a good idea to place a fleck of grease on its threads to try to prevent corrosion. The threads are necessarily fine ones and they have only the wall thickness of the mirror bracket on which to hold, so that very little corrosion results in stripped threads. Do not overtighten, of course.
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