Cleaning the primary, how often do you do it?

[Varangian (John)]

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 (Davin)]

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 (John)]

Originally Posted by 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)

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

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

Thanks to the both of you.

[MrB (Simon)]

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 (Michael)]

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 (John)]

Originally Posted by 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.

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 (John)]

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 (John)]

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

[GraemeT (Graeme)]

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 (Doug)]

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.

[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 (Russell)]

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 (Russell)]

Originally Posted by 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.

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

[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!