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How often should mirrors be cleaned?

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#1 Dutch Countryman

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Posted 27 September 2020 - 08:53 AM

I've had my orion XT6 for two years now.  Is it time to clean the mirrors?  The primary looks a bit speckled, but nothing serious and the views are still great.  When and how often should it be done?



#2 aeajr

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Posted 27 September 2020 - 09:04 AM

If you keep the covers on and store the scope in a dry location you can go for 5-10 years between cleanings.   In fact, if you read your manual it probably tells you to avoid clearing the mirror unless it is REALLY dirty.  A little dust won't hurt anything.

 

What I do, maybe once a year, is put the tube horizontal and put the soft brush on the vacuum cleaner and slide the wand down the tube to pull out any loose dust.  I DON"T touch or even get close to the mirror.

 

I purchased my XT8i used, about 5 years old, and the mirror looked fine.  Didn't touch it for 3 years. Then I finally pulled it out and cleaned it as part of a larger project to flock the tube and put on a dual speed focuser.   Mirror went in beautifully clean.  To be honest, I really didn't notice much of a difference in what I saw from the cleaning.   Flocking the tube had much more of a positive impact because I am surrounded buy a lot of ground light pollution.

 

Likely you should leave the mirror alone.  Try the vacuum cleaner method if you really feel you need to do something. 


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#3 sg6

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Posted 27 September 2020 - 09:08 AM

Depends on you.

If it has more crud on it then you are comfortable with then clean it, with the appropriate thought and care. If you feel fine with whatever then just leave it.

 

Coming from a bit of an optics background if not clean then I clean one.

I do probably look to see if there is anything I can clean off one - think "That looks like a mark that needs cleaning".

 

So I am not the best to ask.


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#4 kathyastro

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Posted 27 September 2020 - 09:10 AM

Mirrors should be cleaned as seldom as possible.  I have had my Newtonian for ten years, and it hasn't needed cleaning yet.


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#5 Asbytec

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Posted 27 September 2020 - 11:41 AM

This article posted by Don seems to suggest a regular "wash" is better.

http://articles.adsa...000303.000.html

Edited by Asbytec, 27 September 2020 - 11:42 AM.

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#6 MitchAlsup

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Posted 27 September 2020 - 01:25 PM

The word to consider if "filthy" and not "dirty"

 

Wait until the mirror is absolutely filthy. Then clean it until it is absolutely perfect.


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#7 Starman1

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Posted 27 September 2020 - 03:52 PM

Why is everyone so afraid to wash their mirrors?

A mirror should be washed NEVER any less than once a year and more often if conditions require it.

 

Reflectivity drops precipitously with dust and haze (microscopic dust adhering through electrostatic attraction) and is restored with cleaning.

You cannot see the drop in reflectivity with the eye by merely looking at the reflection.  Your eye isn't a spectrophotometer.

 

In addition, dew in combination with dust can be alkaline and attack the mirror surface, even the underlying substrate glass.

Salts present in ocean air (within a few miles of the ocean) can attack the surface severely, requiring very frequent cleaning.

Smog in the form of sulfur compounds or ozone can also attack the mirror surface if not kept clean and dry.

My own mirror's coating lasted only 6 years because of that, and the glass underneath needed repolishing.

Live in a city?  You automatically qualify for cleaning more often than once a year to save the coating.

 

If the scope is rarely used, and kept capped, and stored with the mirror vertical rather than horizontal, it might take a while to accumulate enough dust to require cleaning.

But if the scope is used often, the mirror should be cleaned often.

I have learned than mine needs cleaning after about every 40 hours under the stars (before CoViD-19, that was about once every 3 months)--yours may need it more or less often depending on conditions of use.

 

Here is a video on cleaning telescope mirrors and the technique is excellent.

My only caution would be if you know your tap water is alkaline or contains a lot of mineral salts.

If that is the case, you might do all the cleaning in either deionized water or pure distilled water and use a soap containing no skin softeners or lotions.

https://www.youtube....h?v=9Y8xFnXFVGQ

 

So, to the OP, yes, it is time to clean your mirror.  Once you do it, you'll never be afraid to do it again.  It's easy, fast, doesn't damage the mirror, and returns it to essentially new reflectivity (well, with a loss of about 0.5% per year).

Watch the video and laugh--it is that easy.


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#8 Kunama

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Posted 27 September 2020 - 04:13 PM

I wash my primary whenever it is dirty........... usually twice a year ........... prior to Covid my scope was used a lot for outreach, plenty of dust getting kicked into the air by hundreds of lookers.

 

I see a lot of people here chasing "enhanced" coatings to get the last few % of reflectivity and then they let the crud build up on the mirror to the point I would be afraid to use it for shaving.............

 

 

Edit:  Don, just read your post and I agree 100% waytogo.gif


Edited by Kunama, 27 September 2020 - 04:16 PM.

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#9 SteveG

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Posted 27 September 2020 - 04:53 PM

I clean mine about every other year, depending on condition.


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#10 TomK1

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Posted 27 September 2020 - 06:35 PM

I clean my primary mirror about two times per year.   And my secondary a tad less.

 

A couple years ago I went to a star party where a club brought a very large dob ( somewhere around 16 inches) and had it pointed to Albireo.  The club member said the mirror was a Zambuto.   I asked about cleaning and the person was very proud the mirror had not been touched in over 6 years.    My 4 inch refractor showed a more colorful, contrasting star color image than that scope.  I said nothing, thanked him for the view, and felt I made a very good choice purchasing my 11inch Zambuto Teeter STS which shows better images than my refractor.

 

Who knows , maybe the club's mirror had coating failures as well as being dirty?  

 

After 6 years of being stored capped in a dry basement and many gingerly fingertip washings, my primary mirror looks new. My secondary has about eight, grey/magenta tinged 1 to 2 mm dried water type rings.  Cleaning doesn't seem to rid them.   They are kind-of-like an alcohol smear when cleaning an eyepiece except they are very small rings.  The rings are like the type of eyepiece smear which doesn't affect the view.  When I view scenery with the secondary mirror tilted, the view is blindingly bright and sharp.  I handle  the secondary much more gingerly and have sort of given up cleaning the faint rings.  What's bothersome, when I think about it, and I try not to think about it, is.... my dob was delivered with a few ring spots on the secondary, after six years I have a few more rings and my decades old refractor's diagonals are pristine mirror surfaces.  I called Antares when I received my scope and tried cleaning one of the spots with acetone and kimwipe per Antares's recommendation.  Didn't make a difference.  I'm very confident if the secondary was "bad", it would not have been installed and would have been replaced.  So the "bothersome" part is akin to a Tak owner receiving their 130mm refractor and having a hissy fit over a 0.1 mm  scratch under their sliding dew shield... totally, insanely, get a life, ridiculous.   My dob seems to perform like new, unlike my eyes.    

 

When cleaning my primary becomes futile due to failed coating, I'll get it recoated and buy another Antares 1/20 or 1/30 diagonal.


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#11 cuzimthedad

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Posted 27 September 2020 - 06:48 PM

Yeah, I don't get it either. It's just part of the maintenance and upkeep of your scope. When I lived in CA I would wash my 20" mirror 3 or 4 times a year due to all the dust, sulfur, and other chemicals that drifted our way from the valley vineyards. 


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#12 Jon Isaacs

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Posted 27 September 2020 - 06:56 PM

If the scope is rarely used, and kept capped, and stored with the mirror vertical rather than horizontal, it might take a while to accumulate enough dust to require cleaning.

But if the scope is used often, the mirror should be cleaned often.

I have learned than mine needs cleaning after about every 40 hours under the stars (before CoViD-19, that was about once every 3 months)--yours may need it more or less often depending on conditions of use.

 

 

:waytogo:

 

I think it depends on your conditions. I generally clean my mirrors that live in the high desert because of dust. The air is typically dry and free from the acids etc one gets in an urban location.

 

I clean them about twice a year.  I use the technique in Don's link. I've probably been using that technique 10 years. It gets the mirrors clean, bright and shiny.

 

Mirror 25 inch F5.jpg
 
Jon

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#13 RLK1

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Posted 28 September 2020 - 12:35 AM

I think it depends on conditions as well. I live in a drier climate region than starman1 but not as dusty as that described by Jon. Additionally, my 16" scope is vertical in the garage with a mirror cover over the primary and a towel over that which acts as a filter to keep out dust. The scope is covered with an oversized desert storm coat, too. I generally clean it around springtime, once per year. However, a note of caution in the springtime, trees and flowers in meadows near observing sites pollinate in the spring and that yellow stuff in hard to remove from scopes and optics. I definitely check the wind forecasts if I'm driving up to a dark sky site especially in the springtime. 

Nobody's mentioned it but don't overlook cleaning your secondarys, too. They get dusty with reduced reflectivity over time. 


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#14 Notoriousnick

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Posted 28 September 2020 - 04:16 AM

Yes, that pollen is a pest. Lots of it about where I live, too, given that it is springtime. Had to clean the mirror twice in three weeks. No scratches or marks inflicted though grin.gif.



#15 havasman

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Posted 28 September 2020 - 09:57 AM

Yes, for regular cleaning and I only add that distilled water is cheap and readily available. A gallon and certainly no more than two would be plenty for a 6" mirror. I only use distilled water to clean mirrors.


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#16 Glory Eye

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Posted 28 September 2020 - 07:29 PM

"So, to the OP, yes, it is time to clean your mirror.  Once you do it, you'll never be afraid to do it again.  It's easy, fast, doesn't damage the mirror, and returns it to essentially new reflectivity (well, with a loss of about 0.5% per year).Watch the video and laugh--it is that easy."

 

I take at least two dark site trips a month and observe behind my house in between. I fight dust in the country and pollen/dust in the city. My mirror gets coated with a veil pretty quickly. I always debate should I clean it? This statement from Don settles it for me; as long as I clean it correctly, I'm NOT GOING TO HURT it. I was under the impression that cleaning was a trade off because the cleaning itself degrades the mirror. I also think it is a good point to consider that NOT cleaning the mirror could be what shortens the coating life rather than the other way around.


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#17 Glory Eye

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Posted 28 September 2020 - 07:33 PM

I second havasman. After trouble with water spots, I only use distilled water and at .85 per gallon it's easily affordable. Is there such a thing as a maintenance rinse where you don't do a full cleaning but rinse a couple of times with distilled water?



#18 havasman

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Posted 28 September 2020 - 07:54 PM

I second havasman. After trouble with water spots, I only use distilled water and at .85 per gallon it's easily affordable. Is there such a thing as a maintenance rinse where you don't do a full cleaning but rinse a couple of times with distilled water?

For me the maintenance level is blowing the mirror off with a Giotto rocket blower. I do that at the start of every session, an action facilitated by the Starmaster mirror going back in the mirror cell storage box that came with each scope. It's easy to blow the dust off before mounting the mirror cell back in the scope. That makes it really easy to regularly monitor the mirror's condition.



#19 Inkswitch

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Posted 28 September 2020 - 10:51 PM

I do not fear cleaning my mirror but I am a lazy human.  My current 300mm is two years old, has visible dust/dirt, and I have yet to clean it. I used this scope to view PN Abell 55 a couple weeks ago and to view Barnard’s Galaxy during the August new moon despite the dirt. Abell 55 was a challenge but I found Barnard’s to be easy in 21.05 MPSAS. Could I go deeper if it was clean?  I think the answer is a resounding maybe. I’ll take it out and clean it eventually.  Did I mention I am lazy?

 

i also recommend distilled water, at least for the final rinse.



#20 Starman1

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Posted 28 September 2020 - 11:34 PM

I second havasman. After trouble with water spots, I only use distilled water and at .85 per gallon it's easily affordable. Is there such a thing as a maintenance rinse where you don't do a full cleaning but rinse a couple of times with distilled water?

Sure.  It's not a bad idea.  But be cautious--this can "cement" pollen to a mirror, just like dew does.  My dark site gets heavy yellow pine pollen every summer, and that stuff won't come off with just a rinse.


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#21 Jon Isaacs

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Posted 29 September 2020 - 10:12 AM

Sure.  It's not a bad idea.  But be cautious--this can "cement" pollen to a mirror, just like dew does.  My dark site gets heavy yellow pine pollen every summer, and that stuff won't come off with just a rinse.

 

Pollen is a real concern.

 

I find pure dust rinses off.  The last time I cleaned my 22 inch, I rinsed it with both well water and distilled water, it looked bright and shiny so I stopped there.

 

But it's the high desert, no dew, no pollen.

 

I use tap or well water for initial rinsing and cleaning as well as a preliminary final rinse. The final rinse is done with distilled water.

 

I believe in the liberal use of water during the rinse stages,  several gallons for the 22 inch. I don't see any water spots. 

 

Jon



#22 rhetfield

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Posted 29 September 2020 - 11:14 AM

For me, the big concern is the smoky film that also covers all of the house and car windows.  They need cleaning at least once a year in order to see well enough to tell if there is any cosmos outside to look at.  If they need it, the scope does too.


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#23 Keith Rivich

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Posted 29 September 2020 - 04:16 PM

I clean my mirrors at least once a year. Just prior to TSP.

 

If the mirrors get really bad looking I will clean them as needed.

 

My 25" mirror is 24 years old. My 18 around 12 years old. Original coatings. Still look great when cleaned. 


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#24 sunrag

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Posted 29 September 2020 - 06:09 PM

I have cleaned the mirrors on both a 12" and 8".

 

Prior to that, my only experience was cleaning a 4" lens from a refractor. That did not go well, even though I did it very carefully using only highly recommended techniques and materials. After multiple attempts all i got was surface covered with streaks from distilled water (?). It took many many attempts to get rid of most of the haze.

 

So I dreaded cleaning the mirrors fearing I will leave streaks on them. But it was the easiest thing I have cleaned. Following the videos in YouTube, I placed the mirror in the kitchen sink under running water, put a couple of drops of dish soap, and gently rubbed around with my fingers (making sure that the mirror was under water when I was rubbing). Then I gave it a final rinse in distilled water, and leaned it against the wall. Most of water just ran off. Whatever remained, I picked up with the corners of a clean paper towel. At the end, i got a very nice surface with no streaks. 


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#25 Redbetter

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Posted 29 September 2020 - 08:11 PM

Yes, for regular cleaning and I only add that distilled water is cheap and readily available. A gallon and certainly no more than two would be plenty for a 6" mirror. I only use distilled water to clean mirrors.

Distilled water is the way to go since it won't leave streaks and hazes the way tap water can.  (I grew up with extremely hard water...I would never consider using that well water for mirror cleaning.) I get several washings of a 20" (along with who knows how many eyepiece cleanings) from a single gallon of distilled water.

 

I have gone to tap water on the 20" for the initial pre-cleaning rinse.   That saves a lot of distilled water while removing particles.   I only need to use a bowl's worth of water with a drop of soap to do a finger cleaning of the mirror--because I set the mirror level and pour into the parabola.  I tilt the mirror steeply when done and pour distilled water from the neck of my spray bottle for the rinse, spray a few areas, pour a bit more as needed.  After that I wick remaining droplets onto a paper towel/one of those cosmetic pads/ or a Q-tip. 

 

In a year when the weather is cooperative the 20" will spend about 6 nights per month on average being carried in the bed of a truck up to dark skies to observe.  I clean it about 4 times a year when used that heavily.  This year I have cleaned it once...and at the rate we are going it probably won't need cleaned again for the remainder of the year because it isn't making it out to the dark site.  

 

My son's 10" hasn't been cleaned since we bought it, but it has only had a few trips to the dark site, and it is stored capped in the house.  It could use a cleaning now.  I would like to add some wheel barrow handles to it for backyard service...so I probably need to spend some time on it.  


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