Cleaning my dob's primary mirror..

[Chris Stacey]

Being new to astronomy i'm reluctant to do anything without prior advice, particularly if mistakes will cost me money. I've noticed a small black dot (about 1mm wide) about an inch from the edge of the primary mirror of my Dob.

What's the best way to clean the primary mirror? The do's and don'ts for want of a better phrase!

I'd appreciate any help anyone can give me.

[mik]

Don,t bother that small spec will make no odds.

Mick

[Chris Stacey]

That's good to hear, I didn't fancy dismantling it so soon after getting it. Cheers Mick

[mik]

That was a bit of a quick answer from me if your scope is new and you store it with the dust seals on look at it in a couple of years,mirrors can get quite dirty but views will not suffer to a large degree.

Mick.

[EA2007]

Hello Chris,

I have a dobsonian and I have only cleaned it once in 2 years. I know this is probably well-overdue but like you I was nervous of cleaning it. I took the primary from the bottom of the tube and it was covered in a thick layer of grease and grime along with dust and some black specs. All I could see from the open end of the tube prior to this was the black specs, so when you decide to clean it you may see lots more grime. I think that because of where I house my tube (near to the kitchen), over the years it has collected a nice layer of grease (not to say my mothers cooking is unhealthy here!!!), just like a worksurface would or a cooker hood.

I had heard different ways of tackling cleaning, some people say use professional cleaning fluid and a proper cloth, others say, just use a cloth, or a cloth and warm water. One way I found appealing was to use washing-up liquid. But I decided to go for the warm water route and some kitchen roll, later followed by washing-up liquid.

The best thing to do before you start cleaning is to remove dust, this can be done with one of those pump things you get in a camera cleaning kit. An art airbrush or bicycle pump made have the same results.

It pays to clean a small area near the edge of the mirror first, just to see the results, I was happy to see that it cleared the grime well, so I made small circular movements (like on the Karate Kid....wax on, wax off!!) and the results were brilliant. I had no need to use any washing-up liquid, as the warm water alone did the job. Be sure to use soft kitchen roll, that cheap sharp stuff will probably damage your mirror.

I am sure that some people on here may disagree with my method here, but I found it to be very useful, there was no scratching and it did the job well!

[mik]

EA2007 gosh did you,omg dunno what to say you brave person you.

sorry but that is the best how not to clean a mirror tutorial ive seen to date.

not being rude but gosh again.

Mick. :nono:

[EA2007]

Like I said, I am sure that others will disagree. I am open to that concept.

But like I also said, it worked for me...so I don't have any fear of telling others to do the same. Maybe its something in the water here that clean's well. Maybe southern water isn't as good

[mik]

Southern water is ok but don't drink,swim or bathe in it :laughing2:

each to there own and if it worked thats good but the bicycle pump did make me chuckle

Mick.

[EA2007]

I come from a background where I try and use as much stuff as we already have, (recycling!) if you can adapt something for another use then its better than forking out for something new!

A bicycle pump will probably work fine, better than spending I dunno £20 at an art shop for some fancy airbrush! I also use a rear bicycle light for observing, saves paying for a red torch or buying one of those 'specialist' ones from say Celestron! Versatility is a good skill in life!

[FLO]

Your mirror doesn't need cleaning but for the record the usual method for cleaning a large primary mirror is to fill a bowl with water and add a drop or two of mild liquid detergent.

Use a cup to run the water over the mirror surface then wet some surgical cotton-wool balls in the water and very gently wipe the mirror clean - keep changing the cotton balls.

Rinse the mirror off with clean water (use distilled water if you live in a hard-water area) then set the mirror on its edge on some paper towels (to absorb the moisture) to dry.

You might also find this useful:

http://www.youtube.com/opticwavelabs

[EA2007]

There we go.....

[Chris Stacey]

Thank you all for the advice, (and the youtube video), i'll feel a bit more confident now when the time comes. I live in a hard water area so I'm glad that was mentioned.

I work to a very tight budget EA2007, so all money saving tips will always be appreciated

[mik]

From a man that knows stuff... :hello1:

[brympton]

Jeeees a scary video, I liked your idea with the surgical cotton wool balls better than the (being be careful what I say next) use of hands. Oh, is that one of those autocollimator triangles in the centre by the way - still waiting for mine (and James's to show up)

[haitch]

Is that a single black dot? Is it feathered at the edges? Can you see if it is something on the surface of the mirror (i.e. raised up)? Is it a new telescope?

I'm only asking all this as people usually refer to "a spec of dust" but you specifically mentioned a black dot. It is also possible that the black dot is an imperfection in the mirror coating or corrosion of the coating through age or an imperfection in the overcoating and what you are actually doing is looking through the surface of the mirror into the darkness beyond. If your scope is either new or very old I'd take a closer look at that dot.

Don't mean to scare you (recoating isn't too serious when the time arrives anyway) but if it is a new scope I would want it sorting if that was the case.

It won't, as others have said, have any impact on your viewing dust or otherwise but, if it is a single spec of dust, you might be able to remove it by blowing it with a decent dust bubble not a cheapo one out of a camera cleaning kit and not with an air duster can (they can eject liquid and leave marks)

I've cleaned with hands and b.p. cotton wool and I think I prefer the hands method. After all the overcoating on mirrors is, more or less, glass (silicon oxide) and I've never managed to scratch glass with my finger tips.

[barkis]

That guy in the video did his preparation well, I'm not too sure about the using of hands over the surface. If he was an office worker fair enough, if he was a manual worker, and depending on the type of work he did, those hands could have had callouses on them as hard as a nail head, so I would not recommend that. One could fail to remove a ring he may be wearing. Also, There used to be mirror producers who did not overcoat them, the only hardness came from natural oxidisation, and that occurs only over time.

[Chris Stacey]

Is that a single black dot? Is it feathered at the edges? Can you see if it is something on the surface of the mirror (i.e. raised up)? Is it a new telescope?

I'm only asking all this as people usually refer to "a spec of dust" but you specifically mentioned a black dot. It is also possible that the black dot is an imperfection in the mirror coating or corrosion of the coating through age or an imperfection in the overcoating and what you are actually doing is looking through the surface of the mirror into the darkness beyond. If your scope is either new or very old I'd take a closer look at that dot.

Don't mean to scare you (recoating isn't too serious when the time arrives anyway) but if it is a new scope I would want it sorting if that was the case.

It won't, as others have said, have any impact on your viewing dust or otherwise but, if it is a single spec of dust, you might be able to remove it by blowing it with a decent dust bubble not a cheapo one out of a camera cleaning kit and not with an air duster can (they can eject liquid and leave marks)

I've cleaned with hands and b.p. cotton wool and I think I prefer the hands method. After all the overcoating on mirrors is, more or less, glass (silicon oxide) and I've never managed to scratch glass with my finger tips.

It's definately a defined black dot, and slightly raised as opposed to flat to the mirror (from what I can see without removing the mirror anyway).

I bought the scope about 6 weeks ago (brand new) but I was living in suffolk then and i've sinced moved to the Forest of Dean so returning it to the shop I purchased it from would be a non-starter.

I'm assuming the dot isn't an imperfection in the mirror coating or corrosion of the coating since it's a raised dot but do you have any advice or good links about recoating for when the time arrives?

[Chris Stacey]

That guy in the video did his preparation well, I'm not too sure about the using of hands over the surface. If he was an office worker fair enough, if he was a manual worker, and depending on the type of work he did, those hands could have had callouses on them as hard as a nail head, so I would not recommend that. One could fail to remove a ring he may be wearing. Also, There used to be mirror producers who did not overcoat them, the only hardness came from natural oxidisation, and that occurs only over time.

I'm glad you mentioned that, I'm a manual worker who's wrecking his hands by handling metal and chemicals so I won't attempt to do this with my hands now.

[barkis]

That raised blemish on the glass is something that has dropped on to it and hardened. It could have come from anywhere. Something from a bird perhaps, dried blood. You may have had a cut that dripped on there without you being aware. It will come off when the time comes to recoat the mirror. As it is, it will not affect the focused image.

Ron.

[Chris Stacey]

Thanks for the help, Ron.

Now onto my next problem, bought a meade LPI, time to sit down and try and work my way round that now .....i'll look to see if there's any threads on it first before firing questions at people lol.

[barkis]

A little help here for you maybe Chris.

http://www.meade.com/autostar/lpi.html

[Chris Stacey]

Excellent, I see it's got video tutorials at the bottom of the page too. That's what I need.

Thank you again, Ron.

[mdstuart]

Just cleaned my mirror using the water and cotton wool buds and it looks much better...but..just like each time you clean the car you notice more rust, cleaning the mirror has shown me the very minor blemishes on the surface which given the mirror is nine years old it is in good shape...

[haitch]

Yes, that dot sounds best ignored for now. If you're lucky it may soak off when you eventually clean it.

May have missed it being mentioned in a previous post but the cotton wool has to be the surgical stuff for a reason. Even "pure" cotton wool that's not the surgical (or B.P.) variety can contain some man made fibres which are far tougher than the roughest hands.

I must admit to earning my living at this keyboard so if anyone fancies having their mirror touched up... :shock:

[thing]

I've had my scope for a year now and initially it seemed to get covered in black dots. It was just paint coming of the focuser/everywhere else. I cleaned the mirror about 6 months ago and I've only got one more black speck on there since. My guess is it's just paint.