Cleaning the primary, how often do you do it?

[Varangian]

I am sure there has been a poll for this before but I am wrestling with a decision to clean my primary. I have a good strategy and intend to set up properly to do it. Potentially no soap and no cloths/cotton balls, just tap water and hand cleaning followed by distilled water to finish up.
What are your thoughts on this? Cleaning the primary mirror seems to create a bit of a division amongst amateur astronomers. I have a film of dust over mine, nothing major, but if I can optimise my scope's performance through a good clean I think it may be worth while, plus, I'm kinda excited by the proposition of getting the primary in my hands and give it a good clean to feel more connected with the scope (i.e. nurturing).

[bojan]

You do it when it's dirty.. but some dust will not affect performance so much that cleaning is REALLY needed..
I cleaned mine fist time after 10 years, then again after 5 and then after accident when secondary get smashed and pieces of glass fell on the primary.
Now I have some marks on it, but mirror still performs OK and I have big plans for it when I retire ;) (it is 10" f5.6 Coulter Optical, I bought it back in 1980)

[big_dav_2001]

I agree with Bojan, if it ain't broke, why fix it?? Better to have a dirty mirror that still give good views than a clean mirror that's scratched. I've had my scope for almost 10 years and although there's a bit of dust, it still gives views as clearly as when I bought it.

[Varangian]

Sound advice. I wouldn't say the mirror is dirty and I guess I'm just looking for things to do it because of the constant cloud cover here in Melbourne:D

Ultimately though it appears that cleaning your mirror at certain times might be warranted.

Thanks to the both of you.

[MrB]

If there was a foolproof way to do it that was 100% guaranteed to cause zero damage, I'm sure we would all do it regularly!

[MattT]

Every now and then....but it's a refractor does that count? Fracs probably get dirtier being up the other end of a tube.
Matt

[Amunous]

When i went to Wiruna the first time i got a coating of frost on my primary that dried into this awful crust. My views were rubbish for months until i researched how to clean the mirror. The first time i did it i was freaking out that i would scratch the mirror. Being gentle and thorough thou there were no issues. Suffice it to say that the views were a million times better. I have cleaned my mirror a couple of times since then and the more i do it the more confident i am. Even with a small coating of dust there is a massive difference in viewing capabilities.

So long as you are gentle and methodical there should be no issue cleaning it.

[astro_nutt]

I've had my 10" Dob for about 10 years now and I have washed the primary mirror 5 times and the secondary mirror twice. If I see dust on the primary and it doesn't affect the image quality, i'll wait 12 months before I'd think about washing it. The amount of dust covering a primary mirror wouldn't even cover the centreing ring in the middle.
I agree with Michael...as long as you're gentle and methodical, no worries!

[Satchmo]

Theres no option for `as often as i feel necessary' . If my mirrors collect dust from a lot traveling I would wash as often as monthly. Many mirrors based around cities and bushy areas have a grease film from pollution and eucalyptus oil that is pretty tenacious, and cause quite a bit of glow around brighter stars. Breathe on the mirror edge and if the breath pattern comes up blotchy then you have grease to remove.

[Varangian]

Yep I thought of that option post-post. I meant 'all things being equal' kind of scenario (i.e. natural accumulation') rather than the more obscure residue like eucalyptus oil.

The poll is saying, wash your mirror.

[Varangian]

Okay I'm cleaning this bad boy today. I have removed all the screws from the back of the Dob and have lifted out the entire back end holding the primary. I have then loosened all the clips and removed the housing of the mirror and the mirror is now sitting on a shelf in my cupboard waiting for the next step.

My strategy for cleaning includes acquiring a plastic bucket large enough to house the primary. I plan on rinsing it under tepid tap water to loosen up grit followed by immersing the mirror in tepid tap water in the bucket, adding some organic dish washing liquid and gently working my way around the mirror with the pads of the middle finger area. I will then withdraw the primary from the bucket and rinse with tepid tap water and finish up by pouring a bottle of distilled water over it to throughly remove all soap residue and to ensure I get a streak and spot free clean. It will then be left upright to dry before being fitted back into the back end of the dob.

Any thoughts? Anyone got a better strategy for this? Many thanks.

[astro_nutt]

Hi John.
(Disclaimer attached! This is the way I would clean my mirror which has a silicon overcoat)
First, I would prepare the area where I would clean the mirror. In my case I use the laundry trough which has been scrubbed and throughly rinsed clean. Remove the soap holders or anything that may fall into the trough. I have a bench next to the trough in which I place a clean towel.
The other items I need are, distilled water, cotton balls, plain facial tissues, a teaspoon of baby shampoo dissolved in a glass of warm water.
Remove any rings or other jewellary before cleaning.
Soak the mirror in warm water first for about 10 minutes.
Gently lift the mirror out and tilt the mirror to drain the water off.
Rinse the mirror with warm water and put aside on the towel facing up.
Drain and rinse the trough and fill with warm water.
Place the mirror in the water and gradually add more hot water until the temperature reaches about 40 C. (this helps to remove any oil/grease)
Add the dissolved baby shampoo and allow the mirror to soak for another 5 mins.
I gently swish the mirror around for a few minutes, then, rinse with warm tap water and inspect. If it looks clean then it's time to rinse off with distilled water and sit it on it's edge to allow the water to drain off. Any droplet can be absorbed with the corner of a tissue.
If it need a more through cleaning, I would lift the mirror up and out of the water and hold it at a 45 degree angle. I would then soak one of the cotton balls and then, starting from the top edge, draw the cotton ball down across the mirror with only the weight of the cotton ball. As I'm drawing the cotton ball down, I'll slowly lift the cotton ball away from the mirror's surface. When I reach the bottom edge, the cotton ball is place in a container away from the trough.
I'll use a new cotton ball each time, and only clean the area once.
When the mirror has been cleaned, remove, rinse with warm tap water and inspect the surface.
If the mirror looks significantly cleaner then I'll rinse it again with warm tap water followed by distilled water.
If only a few speck of stubborn dirt are still stuck to the mirrors surface, I'll leave them, it's safer!
After rinsing with distilled water, I'll place the mirror leaning on it's edge to allow the water to run off.
Any drops left on the mirror will be soaked up using the corner of a tissue touching the droplet.
When the mirror is cooled, it's then ready to install and collimate!
I hope this helps!
Cheers!

[Varangian]

Thanks astro all done. I took your advice and waited until the mirror had cooled before refitting and collimating.

[GraemeT]

I was faced with this dilemma, as my scope had been in storage for about 3 months. Some bugs and a beetle had managed to find their way into the OTA and the primary was filthy. I was advised years ago not to touch the mirror if it was only dusty, but this was serious carp. Anyway, a bit of moisture on a microfibre cloth worked wonders. As far as I can see, there's no damage to the surface and the image is back to normal!
I guess I'm lucky.

[Pinwheel]

Well after cleaning my primary I caused a much unwanted issue for a whole year, I had bad focus & distortion on my 200mm (8") reflector. I was getting feed up with the problem as it was not fixable no matter how much collimation adjustment I did. Well two days ago I found the problem & thought I'd share my embarrassment but also this may affect other newbies. I discovered that my primary mirror was set back 6mm further back than it should have been. This caused the focal length of the Primary & the secondary mirrors to not focus. Even though my collimation laser showed everything was in line, so moving the mirror forward to 12mm all became sharp & clear. I now know with great hindsight that when I dismantled the primary mirror for cleaning a year ago I failed to note the exact position of the mirror mounted on the primary mirror assembly. I hope this information helps anyone with similar issues. I am now happy to report pin point sharpness of stars & I have been out viewing two nights in a row, & am very happy to be back watching the sky.:D

[astro_nutt]

I know the feeling Doug!..but it's great to find out it wasn't a serious problem and you fixed it!

[rustigsmed]

It would be great if there was a static electricity device you could hover over the mirror (to collect the dust) to minimize risk. I've had my dob since may and am thinking it needs a clean, it's not dirty certainly dusty, my laser collimator isn't a pinpoint anymore when looking at the secondary (due to dust).

[astro_nutt]

Hi Russell.
You could try blowing the dust off with canned air, (available from DS, camera stores, etc) or an air bulb. Use a vacuum cleaner next to the mirror to suck up the dust as you blow it off.

[rustigsmed]

Good ideas ... Will definitely give that a crack, I wonder if a normal air compressor would do the trick. Will investigate, cheers!:thumbsup:

[astro_nutt]

Air sourced from an air compressor may contain traces of oil. (Something you wouldn't want to risk)
An old detergent bottle with a tiny pour nozzle, which has been throughly washed and dried would suffice.
Cheers!

[multiweb]

If you have stubborn stuff on the surface of a mirror or glass your finger tip is still softer than any cotton wool or fabric you'll ever find. You'd be buggered to scratch any coating with soft skin. Added benefit is you can feel any particle on it. When you're done 'shampooing' just rince and blow dry then of course when done keep you finger tips away from it. :)

[MrB]

I recall reading somewhere (may have been the ATMlist) back looong ago when I ground my first mirror, that a clean palm is best when cleaning a mirror?
I know when I was polishing, my fingers left prints or streaks but the plump bit of my palm(muscles for thumb) never did.
Supposedly the palm is soft like fingers, but does not have the greasy/acidic sweat that our fingers do.
This could be complete hogwash due to bad memory tho..... but I must have read it somewhere 'coz I would have done it a hundred times while polishing and it never once scratched or streaked.

[multiweb]

I usually immerse the whole glass in a sink with tap water (warmish) and some of the Kodak photo flow solution. When the mirror is underwater if you lightly touch the surface with your index you can feel any hot spot. Just rub gently until lose. It's super quick to find where the grime is. Then I rinse it in cold water under the tap. The stream of water will run straight off the mirror and grab any isolated drops. Any drop that stays will usually stick to something that shouldn't be on the mirror but with a bit of practice you can 'stick' them to the stream. You can actually rinse your whole mirror dry without even touching it because the water will run off it. What ever drops are left just blow them out of the way and that's it. I know there is an argument about distilled water but in my experience running clean water doesn't leave any marks. In my area anyway. Could be a problem if you have hard water.

[Jon]

I had a strange event, before I got a dew heater or shield, in which condensation (dew) formed on both the inside and outside of my SCT corrector lens, leaving quite palpable marks all over the inside of the lens (the outside stuff evaporated cleanly). Very odd.

I cleaned the lens much as Marc cleaned his mirror in the post above. Very gently in a bowl of clean tap water. Seemed to do the trick and the issue has not recurred.

I can only presume there was some sort of residue from the factory ...

[Marcus10]

Just on this topic, I was watching a DVD produced by Dave Kriege of Obsession Telescopes last night. He had a section in which he demonstrated cleaning a primary.

His recommendation was that a primary should be cleaned once a year. The secondary should be cleaned more often given its greater exposure to dust particles etc.

[Satchmo]

Specifying a recommended time between washes is non-sense. If the mirror looks foggy or unclean - wash it . Refractor users would not let their lenses get into the state reflector mirror owners tend to let their mirrors get into. Why ?

Better still let your mirror become a cess pit - take astrophotos then post a picture of your mirror so people may marvel at how good your pictures were with a dirty mirror :)
http://www.iceinspace.com.au/forum/attachment_browse.php?a=145670

[Shiraz]

when it gets dirty - usually every few months, but can be more often if there is a lot of garbage in the air (eg reaping time).

[Marios]

The idea is to clean when absolutely necessary once you scratch the protective coating on the mirror you will get rust spots.

[sn1987a]

This is the method I use, no need to be squeamish. https://www.youtube.com/watch?v=9Y8xFnXFVGQ

I clean my mirrors when they get dirty which is every couple of months.

[gts055]

Strange options in the poll, I think its its best to clean the primary when its dirty, whenever that may be. Could be years, or days depending on the environment and aggressiveness of the material that lands on the mirror. Mark

[rrussell1962]

What do people think about using acetone as the final stage of cleaning. I have never used it but would be interested to hear other views.

[5ash]

It would have to be analar grade otherwise dissolved impurities might be left behind , also acetone is something I'd be wary of in enclosed areas for both health and fire hazard reasons. Can't really see an advantage as acetone is not miscible with water so would only be of use on a dry mirror.
Philip

[raymo]

I agree with Mark, my preference is not listed as an option. I have
never cleaned a mirror in nearly 50 yrs of owning reflectors, but not because I might harm it, just because I have never observed any
deterioration in the image.
raymo

[dannat]

i use acetone -dont have a problem with it -if the coating is applied properly it shouldn't just wash off.

a mirror with overcoating can be washed fairly frequently -the overcoating should last for ages -
the mirrors without overcoating need more care taken, but i still wash at least once a year in the sink before i do the dishes, rinse with water

I think the more important item should be -how you you prevent your mirror getting dirty -seal the tube as much as possible -& look after the OTA

[Shiraz]

Please be careful with ventilation if using acetone, as Philip warns. In 1963, a senior biochemist at Adelaide University was killed when acetone vapour in his lab exploded.

[Steffen]

Acetone is perfectly miscible with water in any ratio, much like alcohols. I use about 25% water and 75% acetone as my cleaning fluid, this makes cleaning easier as the solution doesn't instantly evaporate (like acetone does).

Cheers
Steffen.

[Don Pensack]

Due to my environment, and the haze that builds up on my mirror, I clean it every 3-4 months. Going longer results in a noticeable loss of brightness and contrast. When I clean the mirror, and make a swipe across the wet mirror, then rinse it off, there is always a shiny streak in an otherwise dull surface.
For my scope, that's one cleaning about every 40-50 hours of use. I couldn't answer the poll because my answer wasn't there.