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Thread: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

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    Default Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors



    With the caveat and promise that there is much more to come (I took more than 2000 photos, but no worries, not all of 'em will be posted...)

    We have completed the bi-annual coating/aluminization of the 82" / 2.1M Otto Struve Telescope Mirrors as of yesterday.

    There is still work to be done before the telescope is back on sky for its first scheduled use, but we are complete with the exception of final collimation, and adjustment of the M1 radial supports.

    Here is a 'teaser' photograph, taken right after we got back the metrology on the mirror coating witness samples. In the wavelength bands of interest, we achieved 94% reflectivity, with an average coating thickness of 980 angstroms.

    Right now, we're under cloudy skies and severe weather watches - we likely won't have sufficiently clear skies to collimate until Sunday night. The telescope is scheduled to come back on-line on Tuesday of next week, for a two-night dedication event honoring the donors that made the f/8 focal reducer and visual back assembly possible.

    More to come...

    IMG_7549w.jpg
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    Default Re: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

    Now That's a mirror. Just a quick question on the collimation. In my simplistic terms, are the collimation/mirror adjusters motor driven, or is this done manually? I would assume its done mechanically with computer commands?
    Mark
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    Default Re: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

    This telescope was designed in the late 1920's, refined in the 1930's, and fabricated between 1932 and 1936. It pre-dates any "modern" electronics, including precision encoders, steppers, servos, etc.

    The entire alignment and collimation procedure is entirely manual, "analog", and represents a balance between brute force (because of the physical sizes and weights) and the delicate ballet of precise, nanometer adjustment, without benefit of any electronics or computer/software support.

    The alignment, and collimation are both visual trial and error processes, based on the human eye, human skill, and deep experience.
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    Default Re: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

    Thanks for the quick answer. I find the whole procedure fascinating and and always enjoy your updates.
    Mark
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    Default Re: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

    Thanks for the fascinating report. I find it amazing that the mirror is resurfaced so often. What is the reason for this? Just to keep it in tip-top shape?
    Michael
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    Default Re: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

    The telescopes are Ritchey-Chretien reflectors, and as such, when in use with the mirror cover open, the mirror is exposed to the environment. Dust, bird poop, insects (particularly moths) provide one source of contamination. The aluminum surface also oxidizes over time. The combined contaminant load and oxidation reduce the mirror's reflectivity over time, hence the periodic re-coating. If the process were not so onerous and risk filled, we would do it more often, probably every three to four months.

    One of the telescopes here, the HET is a segmented-mirror array design - in this case, we have spare mirror segments, which can be incrementally swapped and re-coated - this is done on a six-week rolling interval, so the mirror is more or less always "fresh".
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    Default Re: Coating / Aluminizing the 82" / 2.1M Struve Telescope Mirrors

    That's what I call a well built scope, no computer glitches to worry about just arms and back getting sore. I like the updates Austin . Living life through my eyepiece

 

 

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