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So I just got out my telescope for the first time in a good few months and after coming back inside I’ve found my mirror to be looking rather dusty. 

I didnt check the mirror beforehand, so I don’t know if this happened when I brought it back in just now or if this dust accumulated while I was in Uni. 

I’m trying to fight the urge to remove the mirror and wipe it clean but I know that could scratch it and mike things words. 

Does this mirror look too dusty to you guys? Should I just leave it as is? 

 

(The telescope is a Skyliner-200p dob). 

3398E25D-6B9C-4526-BF1C-4B8E1D02705A.jpeg

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I shared your concerns initially about giving my mirror a bath. However, by following @steppenwolf‘s excellent advice in his “mirror wash” video on you tube, I realised how bathing a mirror is a relatively straightforward task...

Mine was a 350mm Mirror and with careful preparation disassembling, washing and reassembling went well. 

A tip: I disassembled my big Dob by standing it upright and lifting the tube off the mirror cell and I marked each screw and hole with post it notes so they went back in the same holes. 

I also had assistance from my wife in guiding the tube back onto the cell. But other than that it was an easy job. 

I chuckled afterwards when I thought how unnecessary my fear of the task had been. 

Mine wasn’t as dusty as yours. But I do think the wash improved the observing with less scatter afterwards. But I could be imagining that ?

If you do tackle it, watch the online videos, prepare well and it’ll be a simpler task than you currently imagine 

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Dust and grime on the mirror cause light scattering, decreasing contrast. Only you can judge when enough is enough. But as @Stargazer McCabe wrote, with a little help from youtube videos (astronomyshed in my case), it's not that difficult. Just be gentle, and try to avoid actually wiping it. Also, have a tidy and clean workplace before you start.

Good luck

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1 hour ago, Stargazer McCabe said:

I shared your concerns initially about giving my mirror a bath. However, by following @steppenwolf‘s excellent advice in his “mirror wash” video on you tube, I realised how bathing a mirror is a relatively straightforward task...

Here's the link to my video if you decide to clean your mirror.

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Btw, after seeing @steppenwolf's video on youtube, there was another video. The guy in this vedeo didn't use a plastic basin. He used his hands to wash the mirror, which was not emerged in water. He didn't rinse with distilled water, and he placed the mirror to dry on a towel directly on the bench top. Best place to get pulled off by small hands not seeing what daddy put there. Needless to say, his mirror was chipped. Ouch.

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Similar task to that, which Stargazer McCabe followed, only on a 200P like yours, I singularly marked the position of the mirror cell end cap with  the body of the telescope. 
With the scope laying horizontal on my table, I removed the circumferential screws that hold the mirror cell to the tube, then slid the mirror cell off.
With the complete mirror and housing completely detached from the telescope, your better able to closely examine the mirror surface, which differs when trying to view down the scope at focal length?
Its now possible to give the mirror a good cleaning without full detachment from the mirror cell, and once your happy with the clean, realign the mirror cell to the scope, using your ' alignment mark' and re-apply the screws. With careful handling, this task could complete without collimation, provided the mirror itself did not move within the cell that holds it.
A Star test will confirm, and if required, collimate the scope.

Remember, if the mirror itself was dirty, there's every chance there's more dust attached elsewhere inside the tube assembly, so that could require attention too, prior to refitting the mirror cell, just be cautious of the secondary mirror.
 
Also mentioned, the whole task really is less daunting after you have rebuilt the scope for the first time.

Edited by Charic

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Here's my answer....   in short, don't clean it.  It'll look after itself!

 

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I left my 10" 250px mirror 7 yrs before washing it. As others have said, mark the cell/tubes for handyrealignment.

I didnt even remove the mirror from its cell: just laid it in a shower tray and a good rinse with tepid water, then a squirt of washing up liquid and lots of rinsing (I used deionized for the last rinse). A hairdryer on cold is handy to blow away any last beads of water on the mirror surface.

I washed my 15" OMI mirror after 2yrs - and no problems :)

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Lots of good advice already given. I’d like to add :

Best not to check mirrors by shining a light down the tube at night, most look horrid like that. Check in normal daylight.

If you decide to clean, leave it for a few days, then think - is this really necessary?

If you go ahead, get everything you need ready, choose a time when you won’t be disturbed, don’t rush, don’t fuss over every tiny spot or streak.

Don’t start late in the afternoon when it looks like it’s going to be clear........

HTH, Ed.

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3 minutes ago, NGC 1502 said:

Don’t start late in the afternoon when it looks like it’s going to be clear........

HTH, Ed.

Best advice I've seen for a long time ?

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I did against all advice myself and I don't see a problem with cleaning the mirrors once per 1 year and something when they have dust on them (maintenance cleaning more then heavy duty cleaning). For my 8" mirror the, price for recoating is about 200CAD with taxes which it's not very expensive... so I keep my mirrors free of surface contaminants, the views are at their best all the time.

I cleaned my primary twice in less then 3 years, last clean up was 14 months ago and it's still clean enough has I looked yesterday. Some people say just putting water on the mirror will remove some aluminides out of the surface.. but I visually can't see any evidences of that. The mirror is not perfect from the beginning, if you take the primary out and look at the back pointing a strong light, you will see pinholes and the light passing trough the glass, that's normal.

Pouring water on the surface of the mirror doesn't seem to do any damages at all. I put mine in a bowl with mild temperature tap water and a tiny drop of dish soap, let it rest for 1 minutes or so. Then with the mirror inside the water, I pass a medical cotton on the surface to remove the remaining dust, at each pass, a new cotton. Sterile medical cotton without lotion in scaled packaging, with no abrasive inside.

Then rinse of the mirror with tap water and final rinse with distilled water, like 2 liters or so. After that I blow some air on it to move the remaining drops of water out of the surface.

The final result is always impressive, without scratches and the views in my telescope are always optimal too.

Different school of thought, I think dirty optics will eventually cut the resolution in the views. Usually after a bit more then a year of using the telescope once per week, it's full of dust, pollen, cat's hair, etc. With a cleaning per year and a half or so, it will prevent coriaceous dirt accumulation, it's very easy to wipe out everything out of the surface, and the optic look like new all the time. 

--> I speak for a commercial SkyWatcher mirror with a protective coating on it.

 

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I recently wash mine (my 300mm, 200mm, n 130mm) with washing up liquid and gentle rubbing with my hand over the top with all the washing up liquid on it.

they are now so clean I can see my pupils clearly when I look down the tube.

while everyone on YouTube suggest you should never never never touch the mirror, I totally agree if you have claws ?

Edited by lnlarxg
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All this duscussion about mirror cleaning reminds me I must do mine. Dew or maybe frost has created stains on the mirror. And there's also a lot of dust.

Fortunately a sw 6" is easy to dismantle.

Btw 1, I would never wash a mirror that is still in its cell. Water can get trapped. And last time I removed the mirror from its cell, I saw that cork spacers are used as backing for clamps. Water and cork should never go into a long term relationship.

Btw 2, I may replace the black plastic mirror clips with clear plexiglass clips (diy). I want to test if that changes the diffraction. Probably not, an edge is an edge.

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Just cleaned club 10" collapsible dob which had been on loan to a new member

Not sure where he had stored it, and found cob webs in the tube, and cockroach muck on the mirror

Taking outside, just used a wad of cotton wool, damped in distilled water, and dabbed the cockroach muck gently with distilled water

After a couple minutes using fresh wad of cotton wool, and distilled water, gave primary mirror a gently wipe over

Everything came off, and then just wiped with a soft micro cloth, and bingo, nice clean mirror

Left out in sun to allow any water around base of the dob to evaporate

No need to do any rubbing of the primary mirror

 

 

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