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How often should mirrors be cleaned?

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42 replies to this topic

#26 Achernar

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Posted 02 October 2020 - 07:21 AM

Only clean the mirrors when necessary, and don't shine a flashlight into the tube to determine if the mirrors are dirty or not. Every little speck of just will make them look like dirty headlights on your car or truck. But if under normal roomlight you see a heavy buildup of dust or a film, it is time to wash them. However, every time you take them out there is the risk of scratching, or worse, breakage. That and the fact over-cleaning can damage the coatings, is why washing them only when necessary is a good practice.

 

 

Taras

 

 


Edited by Achernar, 02 October 2020 - 07:35 AM.


#27 bandazar

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Posted 02 October 2020 - 08:16 AM

When I used to have my 10" zambuto telescope, cleaning the dust off of the mirror definitely improved views on planets.   If I had a so-so mirror, then maybe it might not have mattered as much.  But I'm speculating on the latter, and am guessing that it probably could not hurt to clean.  The biggest hazard of washing of course was leaving water streaks, and of course the risk of damaging the mirror coating in some way.  If you are accident prone, then maybe having a dirty mirror is better than having a broken/scratched one.


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#28 Asbytec

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Posted 02 October 2020 - 08:53 AM

The paper Starman1 posted on page 1 seems to suggest a regular cleaning to remove contaminates (including the water itself) is the best method. I suppose if your environment is relatively "clean", then you may not need it. But, mine is not. I remove dust after it builds up. Even capped during the monsoon season, but especially under heavy use during the dry season. My fan pulls up a good amount of dust, most of it captured in a breathable filter. Still, it get's dusty with use and running the fan. I clean it more often than generally recommended, and I'm glad to know the paper posted below supports that method. 

 

Here's the link. http://articles.adsa...000303.000.html


Edited by Asbytec, 02 October 2020 - 09:06 AM.


#29 aatt

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Posted 02 October 2020 - 10:46 AM

I use hard well water for cleaning. I follow up with distilled water rinses to wash out the minerals. My scope was not used much last year and there was not distilled water during and after lockdown. So I am on two years without cleaning and it looks it. Waiting for a nice fall day to clean.

#30 robodan

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Posted 17 October 2020 - 03:17 AM

Its not being afraid to clean them, but everytime you do, every so slightly caused minute damage each time, same as lenses and its coatings

#31 Miranda2525

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Posted 17 October 2020 - 03:37 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. 

Incorrect.  Mirrors are exposed to outside air and condensation builds up on it, which must be cleaned at least once a year.  Try looking at the dust buildup when your mirror is sideways with a light source. You'll be amazed. Vacuum cleaner in your telescope?  L0L



#32 aeajr

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Posted 17 October 2020 - 09:04 AM

Incorrect.  Mirrors are exposed to outside air and condensation builds up on it, which must be cleaned at least once a year.  Try looking at the dust buildup when your mirror is sideways with a light source. You'll be amazed. Vacuum cleaner in your telescope?  L0L

As you can see by reading the thread, the opinions are all across the board.

 

Please explain what is wrong with removing the dust within a Newtonian optical tube with a vacuum cleaner without touching the mirror?   Interested in understanding your comment.



#33 Stardust Dave

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Posted 17 October 2020 - 03:21 PM

Cant comment on the vacuum method  .

My scopes had lived in bone dry Northern Ca for their entire lives.

Never had visible condensation on the primary , I've dewed a secondary once or twice (ever) between the 2 Obsessions I have owned, a 15"(traded) and the current 20".

 

The 20" sees use just a few times a month , where as the 13" sees up to a dozen.

It has been posted repeatedly the loss of reflectivity over a period of time. By those numbers the coating should have degraded some measurable amount.

 

Side by side with a brand new 18" star splitter last year , the 1999 20" showed an obvious improvement over the 18"- brighter and more detail on same objects.

 

Can I assume the 20" is still performing at /near its original reflectivity? ( not planning have it tested)

The mirror stays clean and void of stains . Only exception is my site at a high forest meadow , is close enough to main road ( 75 yards or so ) to catch the fine silt of the forest floor when the rare hunter , grower or off-roader wheels by.

 

My remedy is too dry out my mouth and blast a burst of spittle free air across the primary to remove the silt.

Works well. 

The 20" primary has been cleaned roughly every 3-4 years or less.

 

The 13" is clearly in need of a re-coat (pinholes) however objects like the horse-head , Stephan's Quintet are quite visible as are many 14m galaxies on my observing list from my home Bortle 4 location. Roughly 21.56 SQM based on the 5 year old data on ligthpolution.info

 

 Coatings are as old as that 13" scope. Got to be 30 plus years easily.

Not to argue with the facts ,but there are always exceptions. The 13" gets a cleaning most every year as the most used scope.

 

My observations are seat of the pants, no hard science ( or meter) 

Great contrast , and visual impressions about what I'd seen on Steve G's NGC notes using  a 13.1" telescope.


Edited by Stardust Dave, 17 October 2020 - 03:22 PM.


#34 Miranda2525

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Posted 17 October 2020 - 07:15 PM

As you can see by reading the thread, the opinions are all across the board.

Please explain what is wrong with removing the dust within a Newtonian optical tube with a vacuum cleaner without touching the mirror? Interested in understanding your comment.


Facts are posted about when to clean your mirror.

#35 humma kavula

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Posted 24 October 2020 - 10:35 PM

can i ask how its done? i have an orion xt8. ive been seeing videos of guys running water on the mirror in a bathroom sink and using either their finger tips or cotton balls and a drop of dish soap. then rinsing with distilled water and letting it air dry for an hour or so. is this the way its done?


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#36 osbourne one-nil

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Posted 25 October 2020 - 06:27 AM

That's how I've done it the past few times. I like the finger-tip method as it does reassure me I'm not dragging any grit across the mirror. Last time I didn't use distilled water as I didn't have any. I do, however, have very soft water so I don't think there is a high mineral content to leave on the mirror. I tip it on its side and then blow the droplets of water off with a blower bulb. I can't see any difference between this method and the time I used distilled water. 



#37 humma kavula

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Posted 25 October 2020 - 07:54 AM

well today is the day. the mirror needs a bath no joke. 



#38 ButterFly

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Posted 26 October 2020 - 02:22 AM

Its not being afraid to clean them, but everytime you do, every so slightly caused minute damage each time, same as lenses and its coatings

Improper cleaning at any interval may cause damage.

 

Proper cleaning at any interval does not cause damage - it removes the things that attack coatings.

 

I rinse every few weeks.  My mirror is exposed to lots of dirt and dust.  During pollen season, I may need soap.  Every rinse is followed with distilled water because my tap water is hard.  I use a hairdryer on cold to coax the water off quicker.


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#39 Jon Isaacs

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Posted 26 October 2020 - 07:39 AM

well today is the day. the mirror needs a bath no joke. 

 

This is how I clean my mirrors:

 

 

https://youtu.be/9Y8xFnXFVGQ

 

This is what's referred to as the fingertip method.

 

Jon


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#40 Asbytec

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Posted 26 October 2020 - 10:45 AM

This is how I clean my mirrors:


https://youtu.be/9Y8xFnXFVGQ

This is what's referred to as the fingertip method.

Jon


Me too. Recommended.
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#41 osbourne one-nil

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Posted 26 October 2020 - 11:11 AM

Me too...too. 


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#42 icomet

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Posted 26 October 2020 - 11:21 AM

If you don't look at it, then you won't need to clean it.

 

BTW -  the laws of physics states that the larger the optics, the more dust will be attracted/collected.

 

Clear Skies.



#43 TheBrianNebula

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Posted 29 October 2020 - 08:25 PM

This is how I clean my mirrors:

 

 

https://youtu.be/9Y8xFnXFVGQ

This is literally a tutorial for washing dishes lol.gif

 

So THAT'S how it's done!




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