polishing a telescope mirror

rccaulfield

Anyone on here do their own if so can you advise me? Or is there a reliable trader in Dublin that can do it? Mines built up some dirt on it from condensation etc (12 inch)

Popoutman

You'll want to clean the mirror instead of polishing it! Polishing it with anything that has the phrase "polish" in it will have a good chance of either scratching the aluminium surface, or attacking the aluminum.

You have to get the marks and dirt off ideally without touching the mirror as any dust or grit on the mirror will instantly gouge scratches in the mirror that will noticeably lower the contrast in your telescopic views.

You're better off with properly soft wiping towels (not kitchen paper or bogroll - will scratch the aluminium) and a proper cleaning method that is suitable for aluminium coatings:

I'd check out this process here http://www.company7.com/library/clean.html. Company7 work with telescope refurbishment and testing, and their method makes sense and should work without problems.

I would rinse the mirror (held up at an angle in a sink with a few towels laid on the sides and bottom) with distilled water - without using a wiping implement - and leave the water roll off. If there is nothing left on the surface, the water should eventually bead off. You can pick up little droplets that are left behind with a corner of a folded tissue, without touching the surface of the mirror, wicking up the drop. If the only contaminants were water-soluble then you should be good to go.
If there is more stuff to come off you may have to resort to medical grade cottonwool pads soaked with acetone, with a spray of acetone wetting the mirror surface (never having one touch the other when one is dry) and this should be enough. It's hard to do this properly.

The easiest but most expensive way to clean the mirror is to get it re-coated and then storing it properly from then on.

dbran

Hi

Before you decide to go off and clean your mirror first of all you should decide if it really needs cleaning in the first place!! Do not use the "flashlight" test to decide if the mirror needs cleaning.

Even mirrors that are in a professional observatory will have a certain degree of dust on them. A bit of dust should not degrade the optics at all (unless you are trying to do some very very accurate resolving work). However even using the best cleaning methods, you will always leave a degree of tiny scratch marks on the mirror. And if you do a bad cleaning job you will be able to see these scratch marks as visible spikes coming off a bright celestial object.

So unless its really caked in the stuff don't bother cleaning it. The increase in the views may be marginal and if you do a bad job it can cause permanent damage to the mirror.

Hope this helps

dbran

Rubecula

To mirror (LOL) what Dbran says. I have NEVR polished a mirror, the very thought scares the heck out of me.

AND as for cleaning, unless it is really bad, Don't Do It, it really isn't worth it IMO.

rccaulfield

Popoutman wrote: »

You'll want to clean the mirror instead of polishing it! Polishing it with anything that has the phrase "polish" in it will have a good chance of either scratching the aluminium surface, or attacking the aluminum.

You have to get the marks and dirt off ideally without touching the mirror as any dust or grit on the mirror will instantly gouge scratches in the mirror that will noticeably lower the contrast in your telescopic views.

You're better off with properly soft wiping towels (not kitchen paper or bogroll - will scratch the aluminium) and a proper cleaning method that is suitable for aluminium coatings:

I'd check out this process here http://www.company7.com/library/clean.html. Company7 work with telescope refurbishment and testing, and their method makes sense and should work without problems.

I would rinse the mirror (held up at an angle in a sink with a few towels laid on the sides and bottom) with distilled water - without using a wiping implement - and leave the water roll off. If there is nothing left on the surface, the water should eventually bead off. You can pick up little droplets that are left behind with a corner of a folded tissue, without touching the surface of the mirror, wicking up the drop. If the only contaminants were water-soluble then you should be good to go.
If there is more stuff to come off you may have to resort to medical grade cottonwool pads soaked with acetone, with a spray of acetone wetting the mirror surface (never having one touch the other when one is dry) and this should be enough. It's hard to do this properly.

The easiest but most expensive way to clean the mirror is to get it re-coated and then storing it properly from then on.

dbran wrote: »

Hi

Before you decide to go off and clean your mirror first of all you should decide if it really needs cleaning in the first place!! Do not use the "flashlight" test to decide if the mirror needs cleaning.

Even mirrors that are in a professional observatory will have a certain degree of dust on them. A bit of dust should not degrade the optics at all (unless you are trying to do some very very accurate resolving work). However even using the best cleaning methods, you will always leave a degree of tiny scratch marks on the mirror. And if you do a bad cleaning job you will be able to see these scratch marks as visible spikes coming off a bright celestial object.

So unless its really caked in the stuff don't bother cleaning it. The increase in the views may be marginal and if you do a bad job it can cause permanent damage to the mirror.

Hope this helps

dbran

Rubecula wrote: »

To mirror (LOL) what Dbran says. I have NEVR polished a mirror, the very thought scares the heck out of me.

AND as for cleaning, unless it is really bad, Don't Do It, it really isn't worth it IMO.

Thank you all, i'm going to reassess the situation maybe its not worth it, i'll have a good look at it up close tomorrow!

peterako

Hi there,

Firstly...I agree with all that the previous replies have said!

I presume that you are talking about cleaning rather than polishing.

I checked with Astronomy Ireland as they used to clean mirrors, but they do not any more

I have cleaned the mirrors in two of my 8" scopes as they were very dirty and had a lot of 'stuck' dust.

My current main scope had water marks too, which I was worried may have been from rain so....I cleaned it.

BE VERY CAREFULL THOUGH!

A dirty mirror is always better than a scratched on!

If you do find that the mirror is very dirty then this is a great guide and the way I clean my mirrors:

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

It's not that difficult. Be prepared, plan ahead and take your time.

Then you may need to re-collimate after putting it all back together. Which is not too bad too.

Don't be afraid to ask here or PM is you need any more information/help.

Clear skies,
Peter

mossie

peterako wrote: »

Hi there,

Firstly...I agree with all that the previous replies have said!

I presume that you are talking about cleaning rather than polishing.

I checked with Astronomy Ireland as they used to clean mirrors, but they do not any more

I have cleaned the mirrors in two of my 8" scopes as they were very dirty and had a lot of 'stuck' dust.

My current main scope had water marks too, which I was worried may have been from rain so....I cleaned it.

BE VERY CAREFULL THOUGH!

A dirty mirror is always better than a scratched on!

If you do find that the mirror is very dirty then this is a great guide and the way I clean my mirrors:

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

It's not that difficult. Be prepared, plan ahead and take your time.

Then you may need to re-collimate after putting it all back together. Which is not too bad too.

Don't be afraid to ask here or PM is you need any more information/help.

Clear skies,
Peter

I know this thread is a little out of date but it's relevant to me. I came into posession of a reflector from a relative which, unfortunately, had been stored in damp and dusty conditions for 3 years plus. I cleaned the mirror following the above instructions and, even though it's spectacularly different the mirror has a whitish look. It is OK, probably needs collimation, but I wonder if there is something more wrong with the mirror or would more cleaning help? It seems to be fine for casual work so I'm reasonably pleased but any suggestions to further improve it would be welcome. Thanks.

peterako

May be a fungal issue.

Not sure how to deal with that....

Maybe try the guys at IFAS

Peter

mossie

peterako wrote: »

May be a fungal issue.

Not sure how to deal with that....

Maybe try the guys at IFAS

Peter

There was definitely some mildew on there so maybe something similar. Haven't had a real chance to try it out yet given the cloudy weather here so not sure if it's a huge issue. Thanks.