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Does this mirror need to be cleaned?


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Yep, it's dirty, needs cleaning then a re-coat. Just pack it up and send it off. Let the experts do it. Otherwise use it as paperweight.

seems a bit negative? cleaning a mirror is a simple process and although there's clearly a benefit to paying for experts to recoat when needed, in this case the end result seems to suggest that there's a lot of life left before a recoat is necessary.

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seems a bit negative? cleaning a mirror is a simple process and although there's clearly a benefit to paying for experts to recoat when needed, in this case the end result seems to suggest that there's a lot of life left before a recoat is necessary.

No, I'm not being negative. Have you actually seen his mirror? No, nor have I. So going by the photo, it looks as though it does need cleaning and probably re-coat. If a mirror looks 'milky' it's time for a new coating.

If it looks dusty then wash in in distilled water, but if it's both then for a few bucks spent, he gets back a shiny medal. Question is. How did the mirror get so dirty in the first place and why?

I've been an astronomer for 60 years and have built many scopes and observatories in my time for many people and nothing is worse than having a dirty or milky-looking primary mirror.

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the comments subsequent to the OP and the photo after cleaning http://stargazerslounge.com/topic/178676-does-this-mirror-need-to-be-cleaned/#entry1844299 suggest that it's in good enough condition for now to get a good few years' use. I don't debate that a recoat would be a good idea in due course but any benefit currently based on what he tells us in his posts would seem dubious.

surely a few years' use in an open system, would result in a mirror with a fair degree of dust and the odd water stain which I consider normal and certainly not deletorious to the views obtained (except perhaps at very high power on very bright objects and even then....)

clearly you seem very experienced and have a view but dust on a primary certainly does not bother me at all.

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Yep, it's dirty, needs cleaning then a re-coat. Just pack it up and send it off. Let the experts do it. Otherwise use it as paperweight.

No, it didn't need a recoat, the clean has worked fine. Telescope has been in storage for a few years so could be damp or condensation that got to it. Think i'll use it to have a look at Jupiter later rather than using it as a paperweight!

Cheers for the comments all the same.

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No, it didn't need a recoat, the clean has worked fine. Telescope has been in storage for a few years so could be damp or condensation that got to it. Think i'll use it to have a look at Jupiter later rather than using it as a paperweight!

Cheers for the comments all the same.

Glad to hear this, mate. Just make sure the scope's mirror is pointing downward when not in use - stops dirt and dust falling on same.

Aside, many years ago I saw a brand new 12" primary covered in scratches. I asked the owner why is this? and his reply was...."Oh, I just wiped it with this rag".

Turns out the rag was covered in workshop grinding dust! The mirror was stuffed and he had no more money for a new one. It's true, some mothers do have 'em.

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Glad to hear this, mate. Just make sure the scope's mirror is pointing downward when not in use - stops dirt and dust falling on same.

this certainly works with short tube, small reflectors but there's no way I'd leave my 16" five foot long f4 solid tube with the primary mirror pointing down. as with all things we do in life and astronomy, it's about compromise and doing your best with your equipment, budget, skills and experience.

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not sure about that - most moderators love a good debate as much as the next 'man' (we're not all men thankfully), it's when it gets a bit rude, aggressive, personal or against the CoC (or is banging on about the for sale section) that mods get upset. we're members of SGL and astronomers too don't forget. :smiley:

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It's always a bit odd when you read a provocative post on SGL. Generally it's just full of nice people, well that's what I've found anyway.

My mirror will have to be utterly filthy before I'd consider removing and cleaning. I store it standing upright as it came with a bin lid style cover for the primary.

Phil.

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I use 4 different forum's and this one is the most friendly and well mannered of the lot. The least friendly one I rarely post on and mainly use as a source of very good extensive information. If you don't do your research before asking on that one they'll tear you apart!

Sent from my Nexus 7 using Tapatalk 2

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  • 7 months later...

Job done and I'm happy (and relieved!) with the results.

attachicon.gifmirror.jpg

A rinse with tap water followed by soaking in soapy water for 10/15 minutes. Minimal use of cotton wool on the worst area followed by a rinse with tap then deionised water. Just the soaking in the soapy water did most of the cleaning. Safely back in the scope and ready to go. Scope could probably do with a touch up as well!

attachicon.gif8.75 Inch Scope.jpg

Thanks for all the advice and opinions.

Looks good what cleaning agent did you use? :)

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  • 2 weeks later...

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