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Equipment Discussions >> Reflectors

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sixela
Postmaster
*****

Reged: 12/23/04

Loc: Boechout, Belgium
Re: Did I damage my primary mirror?? new [Re: staticclover]
      #6490215 - 04/26/14 04:11 PM

Quote:


I posted some photos of the primary on Google+,




Doesn't look like a healthy coating, if you ask me.

You'll be fine just now, but the GSOs I've seen with a similar appearance tended to evolve badly in time (one of them, though, had been damaged by being stored in a garage and being attacked by aggressive car fumes).

If it's under warranty, I'd talk to the vendor to see what he thinks. Of course, he could argue that it's currently benign, but if it evolves badly just out of warranty...

On the other hand, I'd star test the scope and if the scope star tested to be finer than I expect for that class of scopes, I wouldn't use the warranty (you could get a mirror with a worse figure!)


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Did I damage my primary mirror?? new [Re: sickfish]
      #6490298 - 04/26/14 04:59 PM

Quote:

I have had my dob for 4 years and have not cleaned the mirror once based on what i have read here. I always thought a little dust is fine and just blowing it off and it should be ok. How old is this scope? Is this just age of the mirror?




If your forte' is deepsky you might want to rethink that. And if you enjoy seeking faint moons around planets, again you may want to adopt a more frequent method. Nobody would operate a refractor or cassegrain with the amount of dust a Newtonian can develop in four years on their objective.

Having said that - a sct corrector or refractor objective will stay far cleaner for far longer than a reflector simply because the amount if free space between the dust cover and glass simply doesn't hold anywhere near the dust the inside of a reflectors tube can.

Pete

Edited by azure1961p (04/26/14 05:00 PM)


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Did I damage my primary mirror?? new [Re: azure1961p]
      #6490315 - 04/26/14 05:06 PM

Quote:

You know what - get it recoated.

A ten inch mirror is not expensive to get recoated and you'll like your options the folks out there have to offer on different degrees of reflectivity.

Another thing - and I know Ill draw scorn for this but I'm careful about it and have NEVER introduced a sleek ever. After the typical soapy water thing, I rinse with tap water, then alchohol I leave it on its side to dry .

Ahhh that very pale blue haze at that low angle when studying the mirror. And, a residue spot here and there.

I've resigned to the notion these will NEVER come off chemically ever.

But, I didn't give up...

I open up a fresh box of Kleenex - take several in a loose bundle - MAKING ABSOLUTELY SURE MY FINGERS DON'T TOUCH the part that will contact the mirrors surface.

I give a dry rub a couple times and the haze is gone as are the water spots. And I mean virgin clean.

I give the tissues a fair shake before the dry buff.

There you go. Try it. If its still there - send that baby out and for probably $150 you'll have dandy new coatings better than it ever had and that includes the secondary.

Pete



I agree about the recoating. The first coating may have been applied to a mirror not completely free of debris.

As for not cleaning:
--the mirror surface is not easily scratched when cleaned wet.
--reflectivity can drop >20% in one year (!) on an uncleaned mirror due to dust, pollen, organic materials, and haze. Cleaning the mirror restores the reflectivity, so you're sacrificing a lot of image brightness by not cleaning.
--you should never, ever, rub the dry surface of anything on a dry mirror surface. THAT is guaranteed to leave fine scratches.
--at the least, you should perform a distilled water rinse of the mirror fairly often (2-3X/yr) to get rid of loose dust, pollen, etc. You don't have to rub or anything, just rinse and let dry. Some of the dust that settles on the mirror is alkaline, and, when mixed with dew or simply moist air, can start eating the coating right off the mirror. Rinsing it off will help preserve the coating.


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sickfish
super member


Reged: 01/13/09

Loc: Watertown Ma.
Re: Did I damage my primary mirror?? new [Re: Starman1]
      #6490366 - 04/26/14 05:29 PM

So even if I dont see alot of dust should I still rinse the mirror ?

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Did I damage my primary mirror?? new [Re: sickfish]
      #6490416 - 04/26/14 05:54 PM

Quote:

So even if I don't see a lot of dust should I still rinse the mirror ?



I suppose a lot depends on the storage and use.
A telescope used nightly will require more maintenance than one used once a month.
And a mirror stored vertically will collect a lot less dust than one stored horizontally.
So if there is minuscule dust, perhaps a simple air bulb will blow it off.
But a lot of dust is exceedingly fine, and it is this dust that is more likely to damage the mirror in the presence of moisture.
A mirror used near the ocean will require far more frequent cleaning than one used a hundred miles inland.
Rationality says one should tailor the cleaning to the usage, storage, and conditions of use and storage.
Rinsing is so easy, though, I can't imagine it being a problem to err on the side of caution and rinse more rather than less.


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sickfish
super member


Reged: 01/13/09

Loc: Watertown Ma.
Re: Did I damage my primary mirror?? new [Re: Starman1]
      #6490455 - 04/26/14 06:16 PM

Thanks Don I will pull the mirror off and rinse it. I will try to take a picture before. Also it gives me a chance to try this. I will start a new thread. I am sorry if i hijacked this one. Once again Thanks

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staticclover
member


Reged: 02/12/14

Loc: Clinton, KY
Re: Did I damage my primary mirror?? [Re: sickfish]
      #6490831 - 04/26/14 09:44 PM

No problem at all, as long as it brings Mr Pensack to the conversation!

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staticclover
member


Reged: 02/12/14

Loc: Clinton, KY
Re: Did I damage my primary mirror?? new [Re: staticclover]
      #6501880 - 05/02/14 08:53 AM

I think I am going to let the mirror ride for now. The views look good to me, the stars are pinpoints and the planets look good on good nights. I am new to this and haven't looked through many scopes to know how good it should look. I am going to take another look at it when it's ready for cleaning again.

Can anyone recommend a good place to have the mirror recoated if I go that route?

Know any good articles or videos on how to do a star test properly?


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sixela
Postmaster
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: Did I damage my primary mirror?? new [Re: staticclover]
      #6501932 - 05/02/14 09:26 AM

It's not going to affect the star test. It might make your sky background a tad lighter, but even that is not something I suspect will happen.

All I'm worried of is the longevity of the coating, so if the scope was under warranty I'd contact the vendor.


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craigLambert55
member


Reged: 04/05/14

Loc: Oregon
Re: Did I damage my primary mirror?? new [Re: staticclover]
      #6502001 - 05/02/14 10:03 AM

For future reference, here's the best article I've found on mirror cleaning.

From Mike Lockwood:

http://www.loptics.com/articles/mirrorcare/mirrorcare.html


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Did I damage my primary mirror?? new [Re: craigLambert55]
      #6502801 - 05/02/14 05:41 PM

Quote:

For future reference, here's the best article I've found on mirror cleaning.

From Mike Lockwood:

http://www.loptics.com/articles/mirrorcare/mirrorcare.html



Good article with a lot of common sense.
See also: http://www.youtube.com/watch?v=9Y8xFnXFVGQ
for a video on a gentle, easy, technique for cleaning a mirror.
And see: http://adsabs.harvard.edu/full/1997PASP..109..303M
for an article on why and how often you should clean a mirror.

Edited by Starman1 (05/02/14 05:42 PM)


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Glen A W
professor emeritus


Reged: 07/04/08

Loc: USA
Re: Did I damage my primary mirror?? new [Re: sickfish]
      #6503451 - 05/03/14 12:30 AM

I don't think the mirror looks at all bad. With a high power flashlight, I'd imagine all of mine would look that bad. I've seen much worse in action in large observatories. I have never seen a mirror that looked at all perfect with a flashlight, and many look awful.

I am surprised to hear all this talk of washing mirrors. Though there is nothing to be afraid of if you clean one right, the idea that your reflectance can decrease by 20 percent in a year must only be true if you are living in a very bad area. I've found many scopes can go for years without cleaning.

PS- My Celestron C-10N looked just the same when last I cleaned it, in the Fall. I have not detected any problems. I have a 12" Orion Dob which looks worse because the previous owner let his dog sit it in, and I had to go nuts when cleaning - really not good to do. It is still a good scope to use, and gives great images.

I try not to be too picky, because I haven't found this all to matter much, though for the outright best on Jupiter I have seen some real difference in a really well polished and coated mirror, I must admit.

Glen

Edited by Glen A W (05/03/14 12:36 AM)


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Did I damage my primary mirror?? new [Re: Glen A W]
      #6503492 - 05/03/14 01:56 AM

Glen,
A friend who coats mirrors for a living cleans all the mirrors sent to him, and he has found an average of 25% increase in reflectivity, on each mirror sent to him for recoating, just by cleaning.
Reflectivity decreases from grime on the mirror is real.
But, remember than a 40% loss in reflectivity only loses a magnitude. Unless you regularly look at targets near the scope's limit, that may not be that noticeable to the average observer.


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