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cleaning the primary

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#1 steveinitaly

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Posted 24 February 2010 - 06:05 PM

So I just got my Skywatcher Dob 3 weeks ago. I looked down at the primary and noticed what looks like A LOT of dust. Or is it dew that dried up? It doesnt affect the views but its really annoying knowing that its there. What is the best way to clean the mirror? Take it out? Blow it with air? Throw it away and get a new one? (ok maybe not the throw it away option!)

#2 rockethead26

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Posted 24 February 2010 - 06:11 PM

Check out the 3rd entry down in the "Best of Reflectors" that is stickyed to the top of the list of reflector discussions.

#3 FirstSight

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Posted 24 February 2010 - 06:17 PM

Here's how to clean it sufficiently if you feel it needs it:

1) Take the mirror out - ALL the way out of the scope, its mirror cell and clips;
2) Hold onto mirror firmly underneath while rinsing it off with gently running tap water;
3) Rinse with 1 gallon of pure DISTILLED water.
4) Turn mirror on side while holding firmly onto it by edges/bottom, let drain as much as it will.
5) Let the remainder of the mirror air-dry
6) Replace mirror back into cell/clips, and then reattach cell to scope.
7) When reattaching/tightening CLIPS, remember: their PURPOSE IS to provide a *SAFETY* CATCH to limit the potential for the mirror to fall out or have more than a small amount of room to shift. the purpose is NOT TO CLAMP THE MIRROR INTO POSITION ON THE CELL (despite the use of the word "clamp" to describe the part)! To set the gap between each respective and the mirror properly, insert a clean business-card (or similar card-stock thickness paper) between the clip and mirror, and clamp the clip's screws down to the point where both just bind the card from easily pulling out. Now back off each screw until the card just does freely pull out. That's *just* the right clip setting to avoid "pinching" (distorting) the mirror's optics, while keeping it secure-enough from shifting around excessivley or falling out.

CARDINAL RULES OF CLEANING TELESCOPE MIRRORS:
1) DON'T OVERDO IT; THE PERFECT IS THE ENEMY OF THE GOOD (scratches or erosion of the coating will do more harm than a few small specks and splotches here and there):
2) DON'T SCRUB THE MIRROR, it can be easily scratched, and the coating is extremely thin.
3) DON'T ATTEMPT TO CLEAN A DRY MIRROR SURFACE, ONLY CLEAN WHILE THOROUGHLY WET WITH WATER;
4) UNLESS A SPLOTCH OR SPECK READILY DISLODGES WITH RINSING OR A SINGLE GENTLE SWIPE WITH A GENUINE (not synthetic) COTTOM SWAB, LEAVE IT ALONE.
5) NO SPECK IS WORTH REMOVING IF YOU CAN'T DO IT WITHOUT RISKING SCRATCHING THE MIRROR. See rule #1 above about "perfect being the enemy of the good".

#4 jmb4513

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Posted 24 February 2010 - 06:31 PM

If it doesn't affect the views, don't clean it yet. Think: "once a year" if it really needs it.

#5 FirstSight

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Posted 24 February 2010 - 06:50 PM

If it doesn't affect the views, don't clean it yet. Think: "once a year" if it really needs it.


Gently rinsing it in tap and then distilled water won't hurt it, and will remove most of the dust complained of. It's getting obsessive-compulsive about it and trying to wipe off every last small splotch or speck where most of the risk and potential for scratching the surface or coatings lies, and ditto if you get impatient and try to hurry the drying process with towel-drying (which leaves lint even when it doesn't scratch anything) instead of more prudently, patiently letting the mirror air-dry on its own.

#6 Skylook123

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Posted 24 February 2010 - 07:09 PM

For the last dozen years I've been using a great product from Universal Photonics called #33 BLUE PRE-COTE. It's a blue spray on coating for optical instruments that leaves the mirror as though it was in shrink wrap. When it's removed, it pulls all the dust/dirt with it. Normal use is to protect optics for shipping, but it also makes a great surface cleaner for large mirrors.

Universal Photonics #33 Pre-Cote Linky

AstroSystems used to sell a similar product, but no longer carries it.

It should be used in a well ventilated room with no flame sources.

Steps for using are:

1. Set the mirror on newspaper or other surface that you won't care gets "painted"

2. Using painters tape or masking tape, make a ridge like a dam around the outer edge of the mirror. This is to protect the edges of mirror coating from the product getting under any flaws, and also keeps the surface continuous to the edge.

3. With the tape completely around the outer mirror edge, start spraying. It goes on like spray paint. Scary as the dickens at first, but when you see it work, it's marvelous. Spray generously; no penalty for too much, bad news for not enough to be continuous. It will want to run toward the center of the mirror bowl, but not badly. Just keep spraying until you're sure the surface is well covered, then spray some more.

3. Let it set and dry. For my 18", it probably takes about 30 minutes but I just let it go for an hour or more. As I said, it's used as a protectant for shipping optics and the AstroSystem instructions even recommended spraying it on AFTER the observing session and not removing until the next session for a squeeky clean mirror.

4. When it is completely dry, and then some, pull off the tape around the outer edge of the mirror. Tear a piece of it off and wrap it sticky side out around your fingers. Tap the sticky side against the blue coating anywhere. Pull up. It comes up like shrink wrap, or unwrapping a DVD. Mirror is dust/dirt free.

5. It will not remove stains, like some dew marks. For that I have some special optic cleaner and distilled water. I wet a cotton q-tip or other swab with the cleaner and touch the stain; NO RUBBING! Let it soak into the stain. Then with another q-tip I wet it with the distilled water and retouch the stain. Finally, I use a dry q-tip to wick up any water still remaining, but if I do it right it will be almost too little water residue to see.

I've been doing my 10", 14", and 18" mirrors for the last 12 years with this stuff, about every 18 months since they do get dusty in the Arizona desert. Never had a problem. I even demonstarted it one afternoon when we were bored at the Grand Canyon Star Party. Got some amazed looks when the moderately dusty 18" was just set on my observing table on a couple of layers of newspaper, sprayed with Pre-Cote and nearly caused a few strokes among the astronomers, then an hour later shock and awe as it just pulled off and left a new looking mirror. And not a drop of water on me!

#7 GeneT

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Posted 24 February 2010 - 07:30 PM

Your mirror probably does not need cleaning. Did you look down at the primary using a flashlight?

#8 bobmarleyou812

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Posted 24 February 2010 - 11:01 PM

[/quote]

It's getting obsessive-compulsive about it and trying to wipe off every last small splotch or speck where most of the risk and potential for scratching the surface or coatings lies,
[/quote]

Or cleaning it 3 weeks after you get it. Leave it alone, but in a year don't be afraid to rinse it off.

#9 MrMartin

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Posted 24 February 2010 - 11:49 PM

It's nothing to worry about at all. What is there will have virtually no impact on your observing at all. A few days after getting my XT8i this Christmas I noticed a small black fleck of paint and dust on my mirror when i looked at it in doors. It worried me, until I read on many different websites that the dust will have virtually no effect at all. Everyone's mirrors have dust, no need to worry. Enjoy your new scope!

#10 EJN

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Posted 24 February 2010 - 11:58 PM

Cleaning the primary:

1) Remove mirror from scope

2) Spray with garden hose using a high pressure nozzle
to remove dust particles

3) Apply 1 cap-full of Turtle® ZipWax®

4) Rub thoroughly with a damp clean synthetic chamois,
ShamWow® works well

5) Spray with garden hose again

6) Dry with 1500-watt blow dryer

7) Admire shiny-brite® mirror*











































* :yay:

#11 Alpha Orionis

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Posted 25 February 2010 - 01:02 AM

are you serious^?

#12 Solar Ken

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Posted 26 February 2010 - 05:59 PM

No he's not serious! For those of us who know better, this is kind of funny, but for those who are newcomers and might follow such advice it would be disasterous. For this reason, posts like that one should be immediately deleted by the moderator(s).

#13 steveinitaly

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Posted 26 February 2010 - 06:24 PM

Yeah, I am pretty new at this, but I was pretty sure that EJN was just kidding.

#14 rmollise

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Posted 26 February 2010 - 06:51 PM

So I just got my Skywatcher Dob 3 weeks ago. I looked down at the primary and noticed what looks like A LOT of dust.


Three weeks and you're worried?! :jawdrop:

LEAVE IT ALONE. It will never, ever be free of dust. Forget about dust motes, get the scope outside and drink in the beauty of the sky.

#15 John Kuhl

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Posted 26 February 2010 - 07:30 PM


I don't like to clean my mirrors. Most of the time you will hurt the mirror more than you will help it. However I don't think a dirty mirror will give good views. I use what is called a Rocket-Air. It is a hand held air blower that works very good. Just a quick *BLEEP* and it is good to go. I am anal with my optics being clean, but I try to keep my hands off of them as much as possible. If you are smart about using your scope, you can go a long time without a major clean.

Best, John

#16 DavidC

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Posted 26 February 2010 - 11:05 PM

I would be really carefull about blowing any air on the mirror, for fear of getting moisture on the surface. I lightly spritz my mirror about 3 times a year with a solution of 92% rubbing alcohol and distilled water. Use Brawney paper towels to lightly dab up moisture. Dont use any camel hair brushes, they have been shown to leave micro scratches in the surface.
David






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