Marks on mirror

[Andy274]

Hi guys,

I've got a couple of (what appear to be) marks on the mirror. When I picked up the scope I asked the previous owner if it was dust etc &i was assured there is beijing wrong with it. Reading some of the threads on here I'm not so sure I haven't been led down the garden path...

I'm planning on heading to my local astro club tomorrow & will hopefully ask if someone could take a look & advise me.

What is like to have is an opinion on what my worst case scenario is.

I.e. are they ready to clean, is there a way to refurb them, our do they get replaced.

Also if someone could attach some rough prices for whatever is the done thing, that would be great.

Cheers

Andy

[John]

The chances are that the marks would not affect the performance of the mirror at all. It's quite easy to clean mirrors but it's best not too unless they are really dirty. See what your local astro club think but there is no need to panic

[Moonshane]

I agree with John. Although good coatings are desireable, even an unsilvered mirror will give very good results / images so don't worry too much. dirt has almost no affect upon the image (if any at all) and if there's a small mark in the coatings (or a few) then this will not either.

[Daniel-K]

can you post a pic?

[earth titan]

Rest assured, small marks make no noticeable difference.

My 12" dob has a few small areas where the silvering has become less than perfect and I can't tell.

The general rule which I quite like is the following:

'If you think the mirror needs cleaning, don't. If it really looks like it needs cleaning, still don't. If it really needs doing - DON'T).

If you must clean (I have done so a few times after redoing centre dots or the one time it rained on the primary while I popped inside) then be careful and rinse with distilled (not deoinised) water as it dries with no residue.

[Space Bat]

Mirrors are quite delicate but the cleaning of them isn't quite a daunting prospect if done with care...

But a mirror has to be quite grubby before you would notice any real degradation in performance. Which seldom means the odd spot here and there on the surface - as you couldn't notice any performance issues resulting from such marks...

It is usually total surface area issue - such as the whole mirror has become overly dusty...

This is a good guide from Astro-Baby on cleaning a mirror

Cleaning the Telescope Mirrors

But should only be done if you have a severely dirty mirror as said - and others will say it takes alot to drop the performance of a mirror

[Moonshane]

my advice for cleaning mirrors is ;

1) don't do it unless you really feel the need. sometimes if selling a scope this can help if done with care.

2) take the mirror out of the tube and leave in the cell.

3) remove any electrics like fans

4) soak the immersed mirror/cell in tepid tap water with a little washing up liquid for a few minutes - longer for dirtier

5) rinse off with a standard shower head in the bath etc

6) final rinse with RO water from the fish supplies shop - very cheap.

7) use the corner of a tissue and dab off any big drops of water.

you will note I never touch the mirror and this prevents damage and certainly removes the bulk of the grime if not all of it.

[Andy274]

Thats great news guys - much appreciated.i didn't want to overreact, will see what the local astro club says & will try top post a piccy when I get home

Cheers

Andy

[umadog]

I agree: probably nothing at all to worry about.