Cleaning a Newtonian primary mirror

I too am interested in cleaning my primary mirror. The OCD in me cringes every time I look down at it and I’ve only had it for a few months. I was thinking about getting a squirt gun filled with distilled water and maybe a small amount of detergent to spray it down and the rinse with plain DI water. Would he interested to see what more experienced users do to clean their mirror

Distilled water is a smart choice. You may address some residual not water soluble stuff with Isopropanole. Be careful because this stuff is inflamable and only use it outside. Protect your eyes and try to avoid inhaling its vapor. Avoid any possibility for children to get access to it. It's not a very dangerous substance and easy to handle. It's actually part of a lot of cleaning liquids and you can use it for sensor cleaning too. But it's an alcohol and like any type of alcohol it can act as a poison, can cause dizziness and in bigger amounts unconsciousness.
Admittedly there are better choices to address non-watersoluble residues but they are more expensive, harder to get, harder to handle and harder to dispose so I would not recommend them to anyone who didn't get at least a basic education in dealing with chemicals (Diethylether, Pentane, Hexane).

Clear skies
Wolfgang

andrea tasselli:

Andy Wray:
I'm looking for innovative ways that people clean their Newtonian primary mirror.  In my case I have been totally unable to remove my primary as it seems totally jammed in the OTA tube.

I noticed mine was covered in dust and had some nasty looking things stuck to it (probably just dust, pollen and residue from excessive dew/humidity).  Some of the spots were quite large.

Given I couldn't get at it I resorted eventually to just buying a large bottle of distilled water and pouring it down the tube onto the primary.  I did this repeatedly at different angles and then let it dry.  Whilst it was drying I moved the tube to different angles to make sure the water ran off in different directions.  I surmised that distilled water can't be any worse than all the moisture and dust I see on it from the air.

The result seems pretty good as all the dust and nasty looking things have disappeared and I have no water spots.

This is probably not the recommended way of cleaning a stuck primary, but wondered what other people do?  N.B.  This is the first time I've attempted anything in terms of cleaning the mirror in 4 years.

I had bought some bottles of IPA, but decided that that was overkill and could damage the mirror and/or the inside of the OTA (black paint etc.)

First off, there is no way a mirror cell cannot be removed from a 4 years old scope short of it being soldered down. If you weren't so far down south I'd come myself. This said I wouldn't even start contemplating pouring down water on a mirror cell INSIDE a telescope tube. The proper way is to remove it from the cell, put under the fawcett in the kitchen sink to wash the grittiest bits away then place it in a bowl of lukewarm water with few drops of liquid soap, let it rest for 5 minutes and gently start cleaning the mirror surface with sweeping rolling motions using cotton balls just slightly dragging them on the more stubborn spots, keeping replacing them so that in no case yu're dragging silt over the coating. Wash it with normal water and place it at an angle in the bowl but upright and use a spraying bottle with distilled water and work your way around the whole surface spraying  as you go so that the you replace the whole of the normal water and remove all possible piecses of flint/cotton swab/whatever is left attached to it. The use an hairdryer at no heat setting but at the max power possible and blow away all the water away from the mirro surface. Once this is done, let it to dry. Use surgical gloves in your handling of the mirror all the time.
The end.

BTW, I wouldn't do absolutely anything if the mirror has been used occasionally in a dry environment for just a few years. Dust does not do much of an harm to your images anyways. It needs to be absolutely filthy before you entertain such an idea.

Andrea, I bought the whole caboodle ... gloves, cotton wool balls etc. to do all that you proposed.  I may try just one more time to remove the primary, however it is proving very, very stubborn.  All that said:  it's looking pretty pristine now.  I'm more worried about it being pinched and for that I do need to remove it.  FWIW:  I'm quite a strong guy, so for it not to move at all once I've removed the retaining screws means it is well and truly stuck.  I will try a hot hairdryer on the OTA next to see if I get any movement.

[Update]  Almost burned out my wife's hairdryer trying to get the OTA to expand enough so that I could remove the mirror cell.  It wasn't having any of it.

Andy Wray:

Tim Hawkes:
The method I use is 1) 2 drops of washing up liquid in warm/ tepid water 2) soak for 5 min  3) Support the mirror at an angle 4)  using clean cotton balls - a new one each time - just use the weight of the absorbed water to gently move down the mirror -  start with a new ball of cotton on a new line until all is done 5) rinse and then finally rinse off everything with repeat washes of distilled water.  It has worked so far.

Not being able to get that mirror out is really holding you back I think  -   if you are anywhere near Bracknell UK I would be happy to look at it / compare with my PDS200 to see if it casts any light on the specific problem.

Tim

Tim, I may just take you up on that offer   I live near Yateley, so just down the road.  I could bring my OTA along when you have some time and see if we can work out why my primary is so stuck when so many other people say that it just slides out.

You are welcome .   I don't know how to message privately on this forum but if you send a phone number or E mail  then we can arrange something -  and hopefully I can get my mrs  to relinquish some working space  in the front room :-)

Andy,
I took the mirror mount out of my 200PS this afternoon and washed the mirror. Note its relative position in the scope tube. The mirror mount is a tight fit in the tube and will not budge, so I used a drift on the protruding lip of the mirror mount and gently tapped it all the way round so that it came out bit by bit. It is best to do this with the mirror pointing slightly upwards so that it doesn't suddenly fall out. I have done this before no problem. The emphasis is on gently!

Once out, I took out the mirror, as I was fitting a mask over the clips and filled up the bath with about 6" of tepid water. I  added some detergent which is pure soap and does not contain lanolin. I then supported the mirror in the bath and very gently wiped the surface with soaked cotton wool. Do not press on the cotton wool just let it play gently over the mirror surface. I then removed the mirror and washed it in the shower with tepid water all over, front and back. I finished with pouring triple distilled water all over it and then supported it at an angle to let the water drain off with the mirror sitting on paper towelling. Finally I very carefully picked off any remaining water drops with a piece of paper towel rolled into a point. Keep contact with the mirror to an absolute minimum. Preferably use plastic gloves throughout and wash hands in soap, particularly the finger tips. Do not touch the mirror with your fingers.
Refitting can be tricky because there is a lip on the inside of the scope tube and this prevents refitting the mirror assembly at that point. Very carefully use a flat blade screwdriver to lever out the tube at that point to fit the mirror assembly in. Otherwise it will not fit back in. You may need to ease it in at other points with the end of some feeler gauges, gently tapping as you go.
When refitting the mirror make sure the mirror clips are loose and not pinching the mirror. 
If I am working outside I am very careful to avoid working in sunlight as it is easy to get distracted.

A drift is in this case could be a piece of dowel rod say about 4mm diameter the edge if which is positioned against the rim and the other end is gently tapped with a mallet. Drifts are made of metal and you can look them up on Google.  A metal drift would have a flat end and the whole thing would be tapered so the force from say a pin hammer can be accurately positioned. I used a metal drift I had handy and very gently tapped it with a hammer. Wood may have too much give in it and I haven't tried that I must admit.