Author Topic: Dobsonian primary mirror cleaning  (Read 284 times)

Adam Washington

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Dobsonian primary mirror cleaning
« on: December 29, 2017, 01:31:54 PM »
While collimating my Z12 dob yesterday, I noticed what appeared to be a build up ofdust/dirt/grime/organics on my primary mirrorcaught in the stray light of my laser and red LED headlamp. Thereis not like a ton of stuff on it but enough to notice it in the light. At what point would you remove and clean the primary?

I know there are basically 2 schools of thought on this. One being DONT EVER CLEAN IT, and the other being that its required every couple years or so especially with dobs being that their optics are exposed to the elements.

I found this video on youtube, https://www.youtube....h?v=8rZP7mTEutE ,and these guys seem to know what they're doing and the results looked good but just figured I'd run this by the forum and get some opinions and experience that's superior to my own.

Thanks again...

Alan



pernogori

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Re: Dobsonian primary mirror cleaning
« Reply #1 on: December 29, 2017, 03:16:49 PM »
Can you blow off the buildup gently with compressed air? Can you post a picture of the buildup so we can see how dirty it is?

bersrorexnutg

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Re: Dobsonian primary mirror cleaning
« Reply #2 on: December 30, 2017, 06:20:25 AM »
Alan:

I used to use the cotton ball method that is shown in the video but I now use a simpler, safer and more effective method..

Cleaning your telescope mirror

The mirror is cleaned under water and you use your fingertips rather than the cotton balls. Your fingertips are extremely sensitive and very soft so you can feel any particle that might be on the surface. I have cleaned mirrors up to 25 inches with this technique and I have been very happy with the results.

Jon


risodachest

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Re: Dobsonian primary mirror cleaning
« Reply #3 on: January 01, 2018, 08:04:01 AM »
Quote
Can you blow off the buildup gently with compressed air? Can you post a picture of the buildup so we can see how dirty it is?

While I'd like to post a pic of it, I am also not into removing the primary at this moment. I'll see if I can get a pic of it down the tube using the red LED. Like I said, its not a gross amount and I don't think its adversely affecting my viewing, but just enquiring minds want to know for future reference.

I like the compressed air idea as long as the "dirt" isn't stuck to the primary.

rackramasca

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Re: Dobsonian primary mirror cleaning
« Reply #4 on: January 03, 2018, 08:10:00 AM »
Quote
Alan:

I used to use the cotton ball method that is shown in the video but I now use a simpler, safer and more effective method..

Cleaning your telescope mirror

The mirror is cleaned under water and you use your fingertips rather than the cotton balls. Your fingertips are extremely sensitive and very soft so you can feel any particle that might be on the surface. I have cleaned mirrors up to 25 inches with this technique and I have been very happy with the results.
Jon
I also ran across this video myself. One of my first thoughts that came to mind was the abrasiveness of fingertips vs cotton. On one hand, pardon the pun, I could see excessive pressure from my fingertips catching and dragging particles across the mirror thus resulting in scratches and on the other, I could also see cotton being more abrasive than the skin on of my fingertips.

What to do, what to do...only one shot to get it right or else send the mirror off for recoating if I screwed it up.

Dave Matthews

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Re: Dobsonian primary mirror cleaning
« Reply #5 on: January 03, 2018, 02:02:24 PM »
If it's not too bad leave it alone. Generally I give mine a cleaning once a year using the method Jon Isaacs recommends. In fact that's the method Gary Seronik recommends.

Ronald Bryan

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Re: Dobsonian primary mirror cleaning
« Reply #6 on: January 11, 2018, 06:33:21 AM »
Quote
Quote
Alan:

I used to use the cotton ball method that is shown in the video but I now use a simpler, safer and more effective method..

Cleaning your telescope mirror

The mirror is cleaned under water and you use your fingertips rather than the cotton balls. Your fingertips are extremely sensitive and very soft so you can feel any particle that might be on the surface. I have cleaned mirrors up to 25 inches with this technique and I have been very happy with the results.
Jon
I also ran across this video myself. One of my first thoughts that came to mind was the abrasiveness of fingertips vs cotton. On one hand, pardon the pun, I could see excessive pressure from my fingertips catching and dragging particles across the mirror thus resulting in scratches and on the other, I could also see cotton being more abrasive than the skin on of my fingertips.

What to do, what to do...only one shot to get it right or else send the mirror off for recoating if I screwed it up.

With the cotton, you have no idea how much pressure you are using and if you do catch something, you never know.. With your fingertips, you know exactly how much pressure you are using and you can feel something if you catch it.

I have used both techniques and I'll never use the cotton balls on a mirror again..  With my finger tips, the mirrors come out clean...

As far as when to clean your mirror, shining a flash light on your mirror is guaranteed to make it look dirty.. Just look down the tube with normal room lighting...

Jon

charnhoupito

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Re: Dobsonian primary mirror cleaning
« Reply #7 on: January 11, 2018, 03:34:47 PM »
Last night our kitten crawled inside my 15" dob as I observed Albireo... there were 6 little cat foot prints on the mirror.

For this job I upped my dishsoap content in the water a LOT, and then gently sprayed the mixture on the mirror to lube up the fines (and sand...), let it sit and then sprayed more on to let the junk slide off. This was repeated many times until the stuff was off. Then like Jon I used my fingertips with the water soap mixture on the mirror, very gently moving around. Rinse, repeat etc.

I just got done this job actually and no scratches! The soap is the key (for me, I use Sunlight) and the water is RO.

Freddy Banks

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Re: Dobsonian primary mirror cleaning
« Reply #8 on: January 12, 2018, 04:39:26 AM »
Air compressors MUST be lubricated to survive. Compressed air from those units is contaminated by the lubricants. Multiple stage filtration units can remove most of the contaminants from compressed air. Laboratory filtration can create clean air.

This is the only air compressor I'd use on my mirror and I use it all the time.https://www.walmart....3&wl13=&veh=sem

If you have to shine a light on your mirror to see that it's dirty, it's not dirty.

Eric Lara

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Re: Dobsonian primary mirror cleaning
« Reply #9 on: January 13, 2018, 06:48:53 AM »
Cleaning mirror topics compare well to "oil topics" on a motorcycle forum lolThat said the link Jon provided outlines the method I have used for years now with no issues.....and while it says a final rinse with distilled water is an option, it is not for me....distilled water is cheap and I always use it for the final rinse......I also don't lay it flat for drying but rather prop it up at a steep angle so that most of the droplets run off and those that don't are blown off using a rubber bulb blower.

Nate Flores

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Re: Dobsonian primary mirror cleaning
« Reply #10 on: January 14, 2018, 01:02:25 AM »
My advise is to do nothing if your mirror looks fairly clean under normal daylight illumination. I think more harm can be done by unnecessary
cleaning. If it's just dust (not splotches or blobs) you can use those compressed air cans sold by camera shops, but be careful to to shake the can or hold it in anything but an upright position, or you risk getting some of the propellant sprayed on your optics. In general for dust, I use the compressed air can in conjunction with a broad, very soft sable brush. Good luck!

Ron Abbott

mosretouless

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Re: Dobsonian primary mirror cleaning
« Reply #11 on: January 15, 2018, 10:06:27 PM »
What about the oils in your skin?

telschronexic

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Re: Dobsonian primary mirror cleaning
« Reply #12 on: January 16, 2018, 11:58:21 PM »
The dish soap is a mild de- greaser...

planvelsynchcest

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Re: Dobsonian primary mirror cleaning
« Reply #13 on: January 18, 2018, 06:37:10 AM »
Quote
What about the oils in your skin?
Never been an issue over many many cleanings for me....I do wash my hands well prior to proceeding and since I am using dish soap while cleaning the mirror I wouldn't expect any issues.

Coco Moten

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Re: Dobsonian primary mirror cleaning
« Reply #14 on: January 23, 2018, 01:59:18 AM »
Thank you all, looks like I'll be leaving the cotton out of the equation when the time comes to clean the primary.
How about final rinses?  Distilled water or a 50/50 DW isopropyl alcohol mix?