Collimating and mirror cleaning

[Dave-7]

I searched the forum on some info regarding collimating and mirror cleaning but couldnt find anything. My mirror needs cleaning and collimating, ive seen some youtube vids of people cleaning their mirror with dish washing liquid and their hands however does this not scratch the mirror? Could someone please point me in the right direction.

Dave

[sn1987a]

http://www.youtube.com/watch?v=9Y8xFnXFVGQ


this video is the one I follow.

[Dave-7]

He is touching the surface of the mirror with his hands, does this not scratch the surface?

[Allan_L]

These are the guides I follow

Collimation

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide .htm

Mirror Cleaning

http://www.iceinspace.com.au/63-345-0-0-1-0.html

Good Luck :thumbsup:

[Varangian]

No there is some trepidation involved in this no doubt (I had some myself the first time) but I have cleaned both my 10" and 12" mirror surfaces in the past using warm water and a biodegradable dish liquid with cotton balls / my hands followed by a good rinse. My mirror comes up very clean and, most importantly, undamaged. I rinse the mirror with distilled water to finish and touch dry the spots with a very soft cloth. They're not as fragile as some would have you believe. No probs at all.

[mak15]

I just looked at the collimation site from Alan(above). If it is correct I have spent hour after hour after hour trying to achieve the perfect concentric collimation with my f4.5 12" DOB only to discover that some 'offset' is quite normal in fast Newtonians. If this is correct I will sleep a lot more easily tonight!
Thank you Alan

:thanx: Stew

[RAJAH235]

Yes. Offset is needed.
See > http://www.skyandtelescope.com/howto/diy/3306996.html
& > http://www.skyandtelescope.com/howto/diy/3306876.html

[Pinwheel]

There is caustic soda in dish washing detergent. Use it at your own risk.

[OzStarGazer]

I didn't find out immediately either, but luckily just after a couple of days. Being a perfectionist, I was starting to lose my sleep too. It was a relief to find out!

[OzStarGazer]

About cleaning, I use the same liquid I use to clean camera lenses and it works well. I still have the one they sent me with my camera, but you can buy it at OfficeWorks for little money I think.

[smith89]

For making the mirror cleaning liquid at home, use the pump spray and mix equal parts (http://centurionbarriersystems.com.au/centurion-delineator-barrier/) of water,preferably distilled, and methylated spirits, and spray on the targeted mirror.

[Pinwheel]

If you must use a detergent the safest is a good quality "NON WAX car wash detergent. Car wash detergents are Caustic soda & Acid free, after all who wants a rusty car!!:P

[Renato1]

Last time I cleaned my 14.5" mirror I read everything I could find about the process. One thing I read was NOT to use cotton balls, but to use surgical cotton that comes rolled up in layered paper, because apparently cotton balls may have extra particles in them from the manufacturing process.

That done, I still got some very fine scratch marks on the mirror.

I wish I'd taken the advice of a guy at my club who said he just cleaned the mirror by taking it out and aiming a hose at it, and turning on the tap - then rinsed with distilled water.

My advice, only wash the mirror when it is really, really dirty.
Regards,
Renato

[Steffen]

Are you sure those are scratches, not scuffs or smears?

I almost always rub my mirror when cleaning it (after the initial rinse and soak of course), to get rid of stubborn stuff. I rub with isopropanol and kitchen paper or my fingers, and have never caused the slightest scratch or swirl. That is not surprising either, since the coating of the mirror is silicon dioxide (essentially quartz). That stuff is hard and doesn't scratch easily.

All this talk about cleaning and collimating made me pull apart my Dob for some TLC, incl. mirror wash. It is like new again :) I also fixed a flaw inherent in Bob's Knobs (on the secondary) that has bugged me for ages, and rounded the tips of the screws...

Cheers
Steffen.

[julianh72]

Sorry to be pedantic, but caustic soda is not aggressive to steel, it actually protects steel from corrosion.

(It will chew up just about everything else, though, including paint, aluminium - including aluminised mirror coatings - fats and grease, etc, so yes, many good reasons to avoid caustic soda, but rust ain't one of them.)

[OzStarGazer]

I use a lint free cloth.

[Pinwheel]

Who's talking about steel, I'm concerned about the sensitive mirror coating..Re-read Posts 1 & 8 then 12. You have jumped the gun here!

[Steffen]

Sensitive mirror coating? You may confuse those with anti-reflection coatings on lenses. Those can indeed be damaged by careless cleaning.

Cheers
Steffen.

[bobbyf]

Whilst we are on the subject of collimation, could i have some opinions as to whether mine is in good shape?
Its a 10" F4.7, and the picture was taken with my phone up against an old film holder with a hole in the centre.
The focuser was all the way out, as per the instructions on one of the above links, but i cant see any mirror clips until i move the focuser inwards. They look Ok when i do, but i wondered whether i need to move my secondary mirror to see the clips when the focuser is all the way out.
Any advice you could give would be appreciated
Cheers

Bob

[julianh72]

The post that I responded to:

"who wants a rusty car"

Caustic soda actually PROTECTS exposed steel from rust, so it won't make your car rust, but it is EXTREMELY aggressive to aluminium, and it might damage the paintwork and plastics - and it could well be damaging to at least SOME (but by no means all) optical coatings and mirrors.

Yes, I would definitely avoid using caustic soda products in cleaning any sensitive equipment.

Like I said - "sorry to be pedantic"! :)

[doppler]

I have recently aquired a 10" f4.5 dob salvaged from the tip. The mirror was in bad condition but the scope was not worth spending much $ to get the mirror proffesionaly recoated. I have had reasonable success in doing a home re-silver on the primary. The hardest part was removing the old coatings. Caustic soda is supposed to dissolve aluminium, and yes it did remove a little bit of the coating (I could feel the chemical reaction heat through the rubber gloves) Nitric acid is recomended to remove mirror coatings, but is not an easy chemical to obtain in Aus. My final resort was hydrochloric acid mixed with a trace of copper sulphate (copper reacts with the hydrochloric acid to make a weak nitric acid). Even then it took a lot of hard rubbing to fully clean the old coatings off.

The point here is, the overcoatings are very durable but the area of caution is to avoid scratching the surface. Soak the mirror first then run water over it, I use a spray bottle to remove large dust particles. Then I use cotton wool (under water) to remove the fine dust. I then stand the mirror nearly vertical on a towel and rinse with distilled water.

Cheers Rick

[Steffen]

That's basically what I do too, only I use kitchen paper instead of cotton wool. I also usually need to use isopropanol to get rid of the eucalyptus oil film that deposits on my mirrors.

Cheers
Steffen.

[julianh72]

Errr .... no! There's no nitrates in copper sulphate, so it can't make nitric acid. (Nitric acid passivates aluminium, so I wouldn't have thought it was ideal for stripping aluminium from glass.) Sulphuric acid perhaps, but the hydrochloric acid should do the job anyway, I would have thought.

[Pinwheel]

I worked in the technical division at Selley's Chemicals and the point was never wash a car with dish washing detergent because the Caustic soda causes rust, "So who wants a rusty car" statement was supposed to create a mental image that Caustic Soda is a corrosive not to be used on a Primary mirror surface for cleaning.

[doppler]

My bad....I loved chemistry at school but was never good at formulas for reactions. Caustic soda can remove the aluminium coating but nitric acid is used to disolve silver from a silver coated mirror. A really stong acid is needed to remove the protective overcoat put on commercially manufactured mirrors. I surprised myself that I was able to make a usable coating for the mirror through improvising chemical sources, due to the unavailability of quality chemicals.

"Chemically, nitric acid is made by bubbling nitrogen dioxide into water. So the objective in this approach is to generate nitrogen dioxide. This can be done by reacting hydrochloric acid, a nitrate salt and copper. Around 80grams of sodium nitrate, over 30 grams of copper and 100mL of hydrochloric acid are the quantities needed. The exact amount is not critical. For useable concentrations, the amount of water being converted should be small, around 20-50mL."

[sn1987a]

So strap your mirror to the bonnet and drive through a car wash. Clean mirror, clean car. :P

[doppler]

I found this interesting post about using acetone to clean optics. http://www.rfroyce.com/cleaning_new.htm

[Steffen]

Interesting comment about the Viva towels, they happen to be my medium of choice, too!

Instead of acetone I use Diggers isopropanol, it's easier to work with, doesn't evaporate as quickly and still does the job.

Cheers
Steffen.

[sn1987a]

Hi Bob,

For what it's worth I skipped all that film canister stuff. If you invest in a Glatter laser collimator and the Catseye tool with sight tube all your collimation problems are solved. These tools will last a lifetime so are well worth the investment and make collimation a breeze.:thumbsup:

[bobbyf]

Thanks for your reply Barry, i'll take a look at your suggestions :thumbsup: