Primary mirror cleaning

[jdg600]

I've noticed that the primary mirror on my 2 year old Skyliner 200p has aquired a few spots of dust or dirt and I'm wondering if I should attempt to clean it. If so how do I remove the mirror and how should I clean it.

Any advice would be much appreciated.

[malc-c]

Have a look at Dion's video

[Steve Ward]

If there are just a few spots on it then leave well alone ,

Steve.

[earth titan]

If it's dirty, leave it!

If it's really dirty, leave it!

Having said that I've cleaned 2 of mine. Only after removing centre dots to improve accuracy, so they were done to remove sticky residue.

Rinse with distilled water. De-ionised water is not the same.

Typed by me, using fumms...

[alan potts]

My advice is leave it alone until such time it really needs doing, if it only has a few spots on it then leave it.

Alan.

[jdg600]

Thanks for all the replies. The consensus seems to be that, since its only a few small spots, to leave well alone so that's what I'll do. How will I know when it really needs doing? What sort of image degradation should I be looking for?

John

[NGC 1502]

Thanks for all the replies. The consensus seems to be that, since its only a few small spots, to leave well alone so that's what I'll do. How will I know when it really needs doing? What sort of image degradation should I be looking for? John

Hi John, now this is a very difficult question to answer. i used to be over fussy with clean optics. 10 years ago, I joined my local astronomy club, and was shocked at how grubby some of the members optics were, and surprised at how good the views were. So I'd say the mirrors need to be very dirty to have a noticeable effect.

Perhaps when there is obvious dust and haze all over the mirrors, then a careful clean is in order. But you can see how hard it is to quantify - how much obvious dust & haze do I mean ?

By what you are saying, you are not anywhere near that stage. Best to relax and enjoy the views.

One tip - most mirrors look horrid when you shine a light down the tube at night, check during the day with natural daylight.

Regards, Ed.

[Moonshane]

you could (literally) glue a black disk of some size (maybe even an inch or so diameter) to your primary and not see any sort of effect at the eyepiece. a mirror has to be very dirty to have an effect other than maybe at high powers for brighter objects and even then it's unlikely to actually affect what you can register with your eyes. don't worry about it and just look through the right end.

[Moonshane]

you can clean a mirror to a pretty spotless state without even touching it. just soak it in tepid water for a few minutes, then rinse off with normal tepid water and then RO water from the aquarium supplies shop - very cheap. I then very carefully dab off any residual water with a new piece of kitchen roll (literally just place it on the mirror and let it's own weight soak up the water then take off).

I only tend to do this when selling optics as people seem to worry about it but I never clean my own routinely. I don't even clean eyepieces or very rarely.

sleaks and even scratches will create more problems than a little dust.

[jdg600]

Thanks to all for the helpful resposes. I think I will just relax and enjoy the views as Ed says. One thing did occur to though, I was wondering wether to try simply inverting the tube and maybe giving it a tap to see if this would dislodge some of the dust. The thing that puts me off doing this is that I'm worried that inverting the tube may cause the mirror to drop out . Is this a real danger? If not I may give it a go.

John

[keithatrochdale]

Leave well alone for now.

[Capricorn]

Inverting and giving it a slap might just dislodge the mirror, they are not held in tight as then people complain of mirror pinch.

As to cleaning it, your choice.

It seems taboo to do so, but if you work in optics then things get cleaned 20 times a day and usually with nothing special.

All our Meade SCT's had their correctors cleaned 2 weeks ago, someone had a handkerchief and went round wiping them all.

Strangely they didn't shatter, they didn't turn into a diffuser, they were simply unmarked and cleaner.

[LukeSkywatcher]

If there are just a few spots on it then leave well alone ,

Steve.

Leave it alone. It wont make a difference while observing.

Have a look at this image. Its the mirror of a 20" scope at Kielder and it is still in use:

I just want to give it a blumming good scrub in the bath.

[Bried]

If it's dirty, leave it!

If it's really dirty, leave it!

Having said that I've cleaned 2 of mine. Only after removing centre dots to improve accuracy, so they were done to remove sticky residue.

Rinse with distilled water. De-ionised water is not the same.

Typed by me, using fumms...

I've been wondering about distilled vs de-ionised water for a while now. Anyway, I took the plunge and cleaned my primary as I accidently spat all over it when I tried to blow a piece of dust off.

I couldn't find distilled water anywhere but there was loads of de-ionised water. My thoughts are that using distilled water ensures no deposits are left to dry on the mirror caused by ions in normal tap water (hardwater). So anyway, I thought sod it I'm going to de-ionised water. At the end of the day I want water with a property that ensures no water spots are left on my primary. I'm not really bothered if the water was distilled or de-ionised but just want to be assured that it doesn't contain any cation/anions such as calcium, iron, chloride, sulfate etc.

Anyway, jobs a good un as I've now cleaned my mirror and rinsed with de-ionised water and it's totally spotless and I'm very pleased with the results. So in my very humble opinion I would have to say that although there is a difference in the process by which distilled water and de-ionised water are produced, I believe they both are pure enough to do the job of rinsing a mirror without leaving any deposits behind. If anyone knows any different then I would be glad to hear.

Regards

Brian

[Moonshane]

I use RO water from aquariums. it's just as good as distilled and cheap as chips.

[earth titan]

Distilled water is 'pure' as all the minerals normally present are left in the parent container.

De-ionised water has had the ions removed and nothing else. Still contains the minerals etc that were in the parent water.

Although it makes little difference, optics would prefer 'pure' water.

Interestingly I'm told the ice that forms in the freezer is 'pure' but mine is contaminated with peas :-)

Typed by me on my fone, using fumms... Excuse eny speling errurs.