Dirty secondary

[Joe12345]

A few months ago, I was out with my 8" dob when I wanted to check that it wasn't dewing up. Not thinking properly, I reached inside, and felt the secondary mirror

[beamer3.6m]

I don't know the answer about cleaning but if you do buy a new secondary check out astro boot as they have a number of cheap mirror sets.

However best to wait for other response sea to see if that is even necessary.

[Physopto]

Unfortunately it sounds as though you have rubbed off the silvering from the mirror. The silvering is an aluminium coat that is applied to the surface of the glass and cannot be touched by hand as a general rule. It consists of  a very soft and very thin coat of aluminium evaporated onto the glass surface.

There are several threads on cleaning mirrors, but all will mention to be extremely careful. I would suspect your only recorse is to now see a dealer and get the mirror recoated.

Never touch the mirror with a hand or ever rub it with a cloth. Best approach is to never try to clean either the secondary or primary mirrors unless supervised by an expert or exp;erienced and knowledgeable astromomer.

Sorry to be the bearer of bad news. If you can talk to the dealer who sold you the scope.

Derek

[Moonshane]

It looks like you have just spread the fingerprint grease around the surface.

Take out and clean per the usual method. E.g.

http://m.youtube.com/watch?v=8TObET2F-EA

And may be ok.

[Moonshane]

I presume that the scope still provides decent images as previously?

[Joe12345]

Unfortunately it sounds as though you have rubbed off the silvering from the mirror. The silvering is an aluminium coat that is applied to the surface of the glass and cannot be touched by hand as a general rule. It consists of a very soft and very thin coat of aluminium evaporated onto the glass surface.

There are several threads on cleaning mirrors, but all will mention to be extremely careful. I would suspect your only recorse is to now see a dealer and get the mirror recoated.

Never touch the mirror with a hand or ever rub it with a cloth. Best approach is to never try to clean either the secondary or primary mirrors unless supervised by an expert or exp;erienced and knowledgeable astromomer.

Sorry to be the bearer of bad news. If you can talk to the dealer who sold you the scope.

Derek

I haven't noticed any big differences to the image so I don't want to spend too much money. Would it be cheaper to recoat or replace?

I have attached a photo from a better angle.

[Physopto]

I am not a DOB person I am afraid. But I do know you can get away with quite a bit light loss before you really need to either clean or re-silver a mirror.  I would await other more informed answers from "The DOB Mob" here on SGL before committing to action. If what I can see is a polished off silvering patch, it is very even and central ?

Sorry just realised which bit I am looking at. Does look like the mirroring has gone, as I said not a DOB person!

I would be in no great rush, just await some more replies.

 Best of luck,

Derek

[ronin]

I would clean again if you want to with something like Baader Fluid or simple IPA and a whole load of cotton buds.

This I think would mainly be to keep you happy that it was cleaned with "the right stuff".

Then I would simply use the thing.

It could be that the angle it is viewed from is causing interference with the light and that the resultant colour is a predominence of yellow - the antireflection coatings operate the same way, except they design for a specific wavelength, petrol on water does the same.

Having got a finger print on it then you did the best you could at the time so no fault there. I would suspect it is somewhet of an optical effect, and that if the secondary was removed then you could tilt and view from a variety of angles and see the "colour" alter subtly.

[mapstar]

It looks like you have just spread the fingerprint grease around the surface.

Take out and clean per the usual method. E.g.

And may be ok.

I'd like to see him do that with a 22" lol

Seriously though as a last resort have the mirror out and give it a clean using this method (it should be clinical cotton) but if you haven't noticed a difference I would leave it well alone.

A mirror can be extremely dusty/dirty before it create's any significant degradation in image quality. Warm soapy water then distilled water to wash off (not de-ionised)

Damian

[Moonshane]

This further photo/info suggests there's no major problem

[cjdawson]

Looking at the second image, I think you have got away with it.  I'd suggest that it is worth doing a proper clean of the secondary to make sure that the finger print grease has been properly removed.   If that works then you are all set, no major harm done, just don't do it again ;-)

If there's a problem and things are not back to 100% then it'll be worth taking it along to an expert to get sorted.  If you are not confident that you can clean the mirror properly, this might also be a wise choice, as it's simpler to clean a mirror than to clean then resurface one.

[Joe12345]

So I gave it a clean using distilled water, although with the baader microfiber cloth rather than cotton wool. I can still see stuff on the mirror, but it looks like lots of dust rather than a big patch. There are also a few bigger patches which look like they might have been left by the water.

So what should I do, ignore or replace?

[Physopto]

I would ignore them now.  " If it works don't try to fix it" come to mind. A mirror should never be touched with a hand even if the hand has a microfiber cloth or not. #

The advice was to use clinically clean cotton wool !!

There was  a very good reason for that.  Microfibre cloths unless new ??? and even then they still can harbour sharp particles. A cotton ball loosely held and very gently applied ( and this takes some practice) should be the only thing used. It should be applied soaked in ultra pure water. It should be used once only and discarded. Then use a new ball of cotton wool.

Please        just try the scope without any more cleaning  before you possibly cause irreversible damage if you haven't already!

Derek

[Stu]

I would clean again if you want to with something like Baader Fluid or simple IPA and a whole load of cotton buds.

This I think would mainly be to keep you happy that it was cleaned with "the right stuff".

Then I would simply use the thing.

It could be that the angle it is viewed from is causing interference with the light and that the resultant colour is a predominence of yellow - the antireflection coatings operate the same way, except they design for a specific wavelength, petrol on water does the same.

Having got a finger print on it then you did the best you could at the time so no fault there. I would suspect it is somewhet of an optical effect, and that if the secondary was removed then you could tilt and view from a variety of angles and see the "colour" alter subtly.

Baader Wonderfluid is not suitable for cleaning mirrors

[Moonshane]

Looks fine to me. Great news