Article: Cleaning the Mirrors of a Newtonian Telescope

[iceman]

Hi All

Mike Salway (me :)) has kindly written a how-to article titled Cleaning the Mirrors of a Newtonian Telescope.

You can read the article on the IceInSpace Projects & Articles (http://www.iceinspace.com.au/?projects) page, or directly by clicking on the link below:

Cleaning the Mirrors of a Newtonian Telescope (http://www.iceinspace.com.au/index.php?id=63,345,0,0,1,0)

Many thanks to Mike for writing the article!

If you'd like to submit an article or a review for IceInSpace, it would be much appreciated! Please contact me.

[iceman]

article uploaded.

[stephenmcnelley]

Hi Mike that is a very neatly written article and it's easy to follow, the mirror cleaning subject is not always the easiest one to present verbally or otherwise, and everyone has slightly different ideas on how to do it exactly but you have presented the essentials in a easy to follow way, i am sure it will be popular with many people searching and browsing for help on the subject.
Thumbs up:) :thumbsup:

[tornado33]

Yep, good article. I pretty much followed that method when a fellow IIS Lostock 2006 attendee asked me about cleaning his (overcoated) Newtonian mirror, so I used the kitchen sink in the main house to do it, thanks to the overcoat protecting the underlying aluminium, despite the mirror being quite dirty, after cleaning it was like new.
Scott

[ving]

the exact way i do it :)

i like the way you thanked mike for the article :P

[Starkler]

I do pretty much the same with the exception of a warm rinse of the mirror from the tap to gently flush away loose crud before filling the sink. Loose dust and dirt particles get removed from the equation, leaving mostly solidified softer gunk left.

The less crud that ends up in the soapy bath, the less danger there is of inadvertent scratching of the mirrors coat.

[Gama]

For Mirrors with really bad dirt build up, or stubborn stains, i find this a better method....... Removes all stains !.

[stephenmcnelley]

Innovation plus Gama!

If that is your mirror featured there, i think standing on it with such dirty looking workboots is a bit of a rough practice, surely you could stand beside the mirror while delicately prising the foreign bodies of it with the featured cleansing device:rolleyes: :D

[johnno]

Hi Mike,

A very informative article,and many thanks for your efforts,

Might I suggest,before replacing the mirror, A light going over, with very low pressure compressed air,may remove any particles,that may remain from the paper towell.

I have used paper towell for final cleaning my Binoculars,and Allways end up with small particles,on the lenses.

I use a small air Compressor,with an air nozzle,to get rid of it.

Regards.John

[monoxide]

i'd keep my optics away from compressors as they also blow water/particles (often with rust and junk from inside the tank) if you wanna see whats coming out of your compressor, turn it on and hold the nozzle close to a piece of glass, you'll see spots of nice brown water forming :)


better to use the canned variety!

[iceman]

I wouldn't even use the canned variety - yes you can shake them up but at the start they still blow some liquid out, and if you don't hold them perfectly upright they'll blow liquid out.

Best to use a normal hand-pumped blower that you can get from chemists, camera shops, etc.

[monoxide]

true, but there are canned products that dont use hydrocarbons as the propellant.

apparently the best way to clean a mirror (that most of us wouldnt have access to) is using carbon dioxide (something like a fire extinguisher), the dust and junk on the surface freezes and blows/rolls off, no touching of the optical surface in any way required :)

[Gama]

Freezing it also makes it ice up and stick to the mirror. Back to square 1...

[monoxide]

its actually how they clean the primaries in large observatories :)
like to see someone fit one of them in a sink lol

[Gama]

Actually, believe it not, they use detergent and sponges and mops.. Yes Mops !. Then hose it off.
Here is how the do the 200inch Mt Polamar telescope
http://hpwren.ucsd.edu/news/20061019/

Or the gemini... Pass the bucket please !.
http://www.gemini.edu/index.php?option=content&task=view&id=60

[monoxide]

have a search for co2 snow cleaning :)
btw, mopping your mirror O_O

[bird]

Hi Mike. A good article, basically the same system I follow (I even use the exact brand of demineralised water in your photo).

A couple of suggestions:

- The best water to use is "demineralised", not just distilled. Demineralised will do a better job and evaporate without leaving any residue. (Since you're already using demineralised water this is just a slight correction in terminology).

- New mirrors should be left for at least 3 months before cleaning them. I've been told (and I think it's true) that newly coated mirrors have an overcoat of SiO (silicon monoxide) which over time will oxidise into SiO2 (quartz). Even though the overcoat may be advertised as "quartz" it really starts as the much softer (and porous) SiO which should not be exposed to cleaning.

cheers, Bird

[janoskiss]

Nice article Mike.

Re mirror clamp screws: they tend to come undone sooner or later in transport being so loose. Loctite on the threads is highly recommended.

[dcnicholls]

Mike's process is pretty sound, but I'd be more inclined to use a pure detergent than dishwashing detergent. Most dishwashing detergents have lanolin or a similar oil added, and this can leave residues. So something like Kodak Photo-flo or Ilford Ilfotol (so called "wetting agents") would be preferable. Very dilute Teepol (a Shell product) would also work.

DN

[matt]

Anyone know where I might buy a small air compressor with a variety of nozzles of different lengths???

Many thanks

[dcnicholls]

A cheaper way might be to get a can of compressed air or nitrogen of the sort used by photographers to clean dust off negatives and slides. Photographic shops usually stock this.

Hobby and craft shops sometimes stock small air compressors used for spray painting.

DN

[astro_nutt]

As mentioned in bird's letter..the overcoating has oxidised the mirrors surface on my 10"dob which is quite noticable looking directly at it...however it doesn't seem to affect the image quality!!!...and until it does..I'll leave things as they are and just dust the mirror only when it really needs it!

[bird]

astro_nutt: the oxidation I mentioned was the conversion of the overcoat from its raw form SiO into SiO2 (quartz) over a period of a few months from when the mirror overcoat was applied.

Both of these forms are transparent glass, you won't see any difference between them. The oxidised form SiO2 is much harder than SiO and also more water resistant, so I just wanted to let everyone know that they should wait a couple of months after getting a brand new mirror that's just been coated before cleaning it.

If you have an overcoated mirror then you shouldn't see any oxidation of the aluminium surface at all. I have a 10" mirror here that I was made in early 2004 and it's still just as shiny now as it was when I bought it.

cheers, Bird

[shaneaust]

As I mentioned elsewhere on this forum recently, I had better results when cleaning my mirrors by simply filling the sink with water and a small bit of detergent (as advised in Mike Salway's article on here), then letting the scope soak in it for 10-15 minutes. Then, I took it out, rinsed it with tap water first, then rinsed it with demineralised water. I did not touch the mirror surface with anything to clean it. My mirror had quite a bit of dust and some mildly-greasy gunk on it and the above method worked a trick. I'd tried using cotton balls on it previously to clean it, but they left streaks. So my advice is to just soak and rinse first, and see how the mirror comes up, before touching it with cotton. :thumbsup:

[shaneaust]

I just remembered something from a few years back that I think ya'll might get a chuckle or two from:

I had a mate who went out and bought himself a 6" reflector scope. He was a raw, green, totally inexperienced amateur astronomer, mind.

He called me in a panic several months after he got the scope and said his it was "acting funny". Very upset, he was.

I asked what had happened and he said "I dunno - all I did was run the big mirror in it thru the dishwasher to clean it up good and now the views thru it are really weird-looking!"

:screwy:

Some mothers do 'ave 'em....

[iceman]

oh dear :doh:

[John K]

Great article Mike.
I will never forget going into one of the telescope stores in Melbourne and the sales guy in the store whom I knew from the ASV was having a bit of a chuckle. He said to me "....come check this out...." He then proceeded to show me this 6" reflector and it's mirror that someone had tried to clean with Windex! Apparently the person had the scope only a few weeks and wanted to remove some of the dust on the mirror! Nice.

[John K]

Just a quick question on cleaning mirrors, if you use a hairdryer to blow the remaining water off the surface and dry the mirrror, is that likely to have a detrimental affect on the coatings or mirror at all?

[PeteMo]

Mike
Thanks for your article as it is very comprehensive. Especially like the use of loads of photos to show you what to do, rahter than just tell.

At the moment I use Isopropyl Alcohol from my camera lens cleaning kit to clean my mirrors.

Just to prove how much difference a dusty mirror makes to your viewing pleasure, a lot of dust recently collected on my primary mirror. I carefully cleaned off the dust and re-inserted the mirror. I also had to dust off the secondary mirror. The difference was a noticeable improvement in clarity and an increase in brightness.

I find with aerosol dust canisters that you need to get the nozzle close to the mirror or lens you want to blow the dust off, and unfortunately, often squirt some of the fluid that hasn't vapourised onto your mirror, so I prefer using my camera lens brushes, isoproply alcohol and lens tissues.

Next time I'll use your article to clean the mirrors.

Thanks again for tackling a taboo topic.

[matt]

Just make sure you use low heat

[Dobman]

Great article Mike, I'm about to clean my 12" mirror for the first time in 4 years and feel a lot more confident about doing it now.
One piece of advice i heard somewhere was to make sure you swing the tap to one side once you've finished so you dont accidentally clunk the mirror on it when taking it out of the sink
One question i do have is; is there any reason why you cant leave the mirror in the holder when you clean it? It would save the bother of removing it.
Any thoughts on this?

Simon

[iceman]

Hi Simon

With my 12", it doesn't come out of the mirror cell so I leave it in and there's no problems with that.

I'm glad the article was helpful!

[erick]

Yes, and don't worry if you have a fan installed. I've seen that go through the washing and rinsing and work fine once all is dried out.

[astronut]

Whilst dunking the whole lot into the bucket is the easiest way, your poor old fan will eventually give up.:lol:
When this happens you will have to remove the mirror to get to the screw heads to remove the dead fan.
I removed my LB's 12" mirror and carefully removed the left over bits of adhesive tape from it and the cell.
You can then unscrew the fan (and replace it) then you can reverse the position of the screws so that the heads are on the outside.
The new fan can then be removed before the mirror has its next bath.:lol:
To relocate the mirror into the cell, I used adhesive backed velcro.
It works very well, allowing the mirror to contract and expand as necessary.
This was a recommendation by Mark Sutching (Satchmo) a very well known mirror maker. :thumbsup:

[fok4tel]

My LB16's mirror won't come out either, it is held securely with black silicone adhesive. I thought of chucking the whole cell assembly into the water, but I had second thought. I don't know what the mirror cell is made of. If it is steel then it will rust. Also, the collimation bolt holes are full of grease, I'm afraid the grease will pollute the soapy water and the mirror, and even if the grease is totally washed/dissolved, the bolt holes will be exposed and corrosion will happen. So I see that sinking the whole thing is a messy stuff that I'll try to avoid.
Also, has anybody cleaned their secondary mirror before? I see that the secondary is glued to the holder with some whitish stuff, which I don't know how to remove. And even if I eventually remove it, what kind of adhesive should I use to put it in place again after cleaning?
Thanks.

[iceman]

I have cleaned my secondary in the same way as the primary. It's such a small mirror. You don't really need to take it out of the holder. At least, I don't.

I just hold the mirror above the water and clean it as per usual.

[fok4tel]

Thanks Mike. Do you just detached the secondary holder from its spiders or you take the whole holder-spiders assembly out?

[erick]

Whichever you do, make sure you have the tube horizontal so nothing drops onto the primary - apologies if that is obvious, but it has been known to happen.

[neilallison]

Great article Mike.

How much time would you recommend putting aside to do this task?

[sn1987a]

I found this youtube video very helpful.

http://www.youtube.com/watch?v=9Y8xFnXFVGQ