Telescope mirror

[Ian S CParticipant @iansc]

I bought a telescope at a garage sale today, it's been stored in a dusty shed for a number of years, and the mirrors need cleaning, what is my best way of doing this. I also have to get the spider webs out from within, no problem there. It is a Mirador. D=85 mm f= 840 mm. Made in Japan.

Ian S C

[Ian S CParticipant @iansc]

[john carruthersParticipant @johncarruthers46255]

Do not rub them.
Unless they are like the bottom of a dustbin, leave well alone. The micro scratches caused by cleaning can have a worse effect on the image than the dust.
In times gone by, before coatings, a mirror would be left to tarnish and give a better image.

If you must clean them, rinse under running water to sluice off the worst, do not rub.
Then let it soak in a very mild detergent for an hour or so, then gently swab with pure cotton balls in one direction, changing often, with no pressure, just it's own weight. Rinse with distilled water.
If there is any persistent debris you can use pure IPA, then rinse as before.
Pollen is the worst offender, tenacious stuff.
If there are many large holes in the silver (aluminium usually) then get them re-coated. With care and a clean salt free atmosphere they can last decades.

[AjohnwParticipant @ajohnw51620]

I sold a truly filthy mirror in a telescope to some one at a price that assumed the buyer would have to get the mirror recoated.

He later took great glee in telling me he had cleaned it without any problems. He stuck it under a tepid shower for while. I doubt if he used needle jets or etc coming out of the shower, more like moderately heavy rain. It wouldn't hurt to toss in a bit of soap now and again as long as it's left under long enough to wash it off.

So if it was me I would soak it in soapy water for a while not attempting to get off any grime and then into the shower.

Most telescope mirrors are over coated with something which makes them tougher than straight aluminising. I did try to clean up a mirror in a microscope part that wasn't coated. The slightest touch with a very wet cotton bud that had been teased out to make it into a sort of mop scratched it. A Nikon part but it turned out that it had been made in the USA. Nikon proper would always overcoat.

John

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[BizibilderParticipant @bizibilder]

Wash it in luke-warm soapy water – a few drops of washing up liquid in a bucket full of water will do. If necessary you could very gently wipe it with cotton wool whilst it is in the soapy water. Rinse with copious amounts of cold water, followed by a final rinse with distilled water (or water from a water filter if you don't have distilled). Prop the mirror on its side to drain and dry.

[AjohnwParticipant @ajohnw51620]

If you follow John's advice and rub do try a tiny area that doesn't matter first just in case there is no over coating.

John

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[Ian S CParticipant @iansc]

Thanks guys, getting the thing back together now. Next thing is to make some sort of stand for it.

Ian S C It's all Neil's fault.

[Neil WyattModerator @neilwyatt]

Suggestions for first targets at the moment:

• Jupiter
• Orion's sword (M42 nebula)
• Pleiades (can you see these from NZ?)
• Praesepe in Cancer

Plus all those wonderful things you have down south we can't see like the magellanic clouds.

Neil

[Ian S CParticipant @iansc]

Been out to have a look at Jupiter, just a few degrees east of the moon, and the moon, but just like when I built a wind turbine, and the wind didn't blow for over a week, the clouds came in after a clear day. Got it mounted on my camera tripod, a bit flimsy, and adjustment is a bit coarse.

Ian S C

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