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Dust on a primary Mirror


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Now this may well seem like a bit of a stupid question but it comes from someone that has all his mirror covered with glass plates of one type of another.

 I now have an open mirror sitting here on the floor awating some other parts to turn it into as fine scope.

What is sites view on blowing dust from a Mirror using these cans of compressed air that I guess are for removing dust from laptops keyboards and covering the nearby scope mirror. I know someone that blows dust off camera lenses with such but maybe this is a more refined type than the supermarket sells.

Alan.

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HI Alan,

I was going to give you the three steps to cleaning mirrors, but a can of compressed air should shift the loose stuff. Keep it upright as if you do not the propellant will hit your lovely coated optics. You need a proper photograhic quality puffer brush to get the rest off. plenty of vids online if you are going to wash the mirror, oh and Baader wonder fluid is not recommended for mirrors.

Good Luck

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I once used such a can - never again 

It left a nasty streak across the mirror. I then had to remove the mirror and gently wash it (following the steps for cleaning a mirror).

If you are going to use the can then make sure you start "squirting" the air out away from the mirror and then move the can towards the mirror (hope that makes sense).

Most of the liquid comes out in the first moments of squirting.

Lee

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It don't seem to sound like a good idea, The mirror doesn't need a clean, it's new, but I always like to know these things well before I am ever going to do the job. I took the front off the SC a while before Christmas took one look at the primary and left it alone, the secondary had a few marks on it at I used to store it vertical, so it got a wash.

I am sure all you members of the Dob Mob will keep me on the straight and narrow. The othe part of the scope must be close now as we have 4 solid days of a mix of snow and rain just starting, weather don't you just love it.

Alan

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hi alan, as all others have said, the cans of compressed air do expel liquid propellant and will leave a mark, it wont damage it but will annoy the hell out of you. just use a bulb blower :smiley: hope the rest turns up soon. look foward to your report

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If you keep the can vertical you do not get propellant egress from the nozzle. If you shake the can or hold it off the vertical = propellant.

Good point Damien although its not always easy holding a can upright when trying to blow dust of a large mirror, Alan's an 18" 

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Bulb blower for sure, there is then 100% nothing to go wrong.....and after this I wouldn't touch the optics physically, with anything.

A bit of dust won't effect the performance of your scope.

I have a couple of newts (no-where near the size of yours though!) and my own personal rules are:

1) If mirror looks dusty, it's ok. 

2) If mirror looks very dirty, then postpone cleaning it for 12 months.

3) When 12 months comes around, refer again to (2). 

The ever so slight degrade in mirror performance from a huge amount of dust is greatly preferred to the risk of fine micro-scratches on the surface.  Which totally knacker your views, trust me.

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I think Mike it was in a thread with Richard and yourself I joked about the scope going to the UK. Well two parts, mirror box and poles came last week but the base and secondary cage went to England from Holland, this clearly a mistake, they happen, too often but they happen.  It was shipped to Germany from the UK but it was heart set on coming to see you so went back to England for the second time in 4 days, something I have never done myself once being a fitting on a KLM aircraft. England then thought it had better go back to Germany, I had money on it going back to Holland as well.

Anyway it's on it's way being in Romania last night but it could still make a last ditch effort to come over again, it clearly wanted to be with Richards Sumerian. Maybe it was love!

Alan

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I think Mike it was in a thread with Richard and yourself I joked about the scope going to the UK. Well two parts, mirror box and poles came last week but the base and secondary cage went to England from Holland, this clearly a mistake, they happen, too often but they happen.  It was shipped to Germany from the UK but it was heart set on coming to see you so went back to England for the second time in 4 days, something I have never done myself once being a fitting on a KLM aircraft. England then thought it had better go back to Germany, I had money on it going back to Holland as well.

Anyway it's on it's way being in Romania last night but it could still make a last ditch effort to come over again, it clearly wanted to be with Richards Sumerian. Maybe it was love!

Alan

i have read your reports alan, what a nightmare , i would suggest you just send it to me as we have good skys at the moment and its a barmy 14* outside. i can then do a first light report for you :smiley:

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I read on another thread that (ignoring heat plumes) if you put your finger in front of the objective, this would not create a discernible decrease in contrast or anything else. Therefore a little dust being much less dense and covering less area will hardly be different.

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The three steps I was going to provide the OP with was omitted as, not only is the OP a moderator with a gozillian posts, he had already detached the mirror from the housing and was asking the opinion of the site, and as the vastness of the mirror was not mentioned. He received the original reply.

I should have sent the three steps to cleaning the mirror and not be suaded by his status :--

1. Make cup of tea.

2. Think about cleaning mirror.

3. If thirsty goto step 1.

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Another danger is having the thin blow tube blow off the nozzle from the pressure and hit the mirror surface. Don't ask me now i know this. Never again for me. Hand blower only. I do use a hair drier no heat to dry mirrors right after cleaning them and rinsing them with distilled water.

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Brillo pad?

:eek:

I read on another thread that (ignoring heat plumes) if you put your finger in front of the objective, this would not create a discernible decrease in contrast or anything else. Therefore a little dust being much less dense and covering less area will hardly be different.

Well, you can't see the gert big secondary, so I wouldn't get too excited by a few spots of dust.

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I think Mike it was in a thread with Richard and yourself I joked about the scope going to the UK. Well two parts, mirror box and poles came last week but the base and secondary cage went to England from Holland, this clearly a mistake, they happen, too often but they happen.  It was shipped to Germany from the UK but it was heart set on coming to see you so went back to England for the second time in 4 days, something I have never done myself once being a fitting on a KLM aircraft. England then thought it had better go back to Germany, I had money on it going back to Holland as well.

Anyway it's on it's way being in Romania last night but it could still make a last ditch effort to come over again, it clearly wanted to be with Richards Sumerian. Maybe it was love!

Alan

CRICKEY Alan, so your parts have had 2 "sling shots" around the UK, 1 "slingshot" around Holland - the speed the parts are going to be travelling you'll have a job attaching the mirror - just wait for the "skype" from the surface of Mars at this rate!!! - surface detail will be nice - may even get a rover or 2 in the background - not even a speck of dust in sight!!

Paul.

Just thought a well Alan - with you now joining the DobMob- could this be the next location - just think of it - Dobfest 6 (How the Martians do it!!) - virtually no light pollution - come to think of it No Atmosphere, No Air - but really clean mirrors!!

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The trouble with spay cans is that they are not all made equal you can get proper ones for cleaning optics that contain no propellant and are perfectly safe for mirrors, sensors etc,

Dust in itself is fine provided its not mixed with any gooey subsance that can provide a medium for acid or fungus deposits to take hold.

Alan

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I reckon a new mirror is purposefully pre statically charged at no extra cost, so that it successfully attracts a dismaying amount of dust in the first few mins - to get the new owner to face into the anxiety of a dirty mirror straight away! Likewise all dobs are shipped intentionally miscollimated... :) :)

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I reckon a new mirror is purposefully pre statically charged at no extra cost, so that it successfully attracts a dismaying amount of dust in the first few mins - to get the new owner to face into the anxiety of a dirty mirror straight away! Likewise all dobs are shipped intentionally miscollimated... :) :)

LOL, I've got one of them too!

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