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Primary mirror cleaning

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Anyone tell me their preferred method of cleaning the primary mirror on a newtonian and is there anything to coat it with to keep it cleaner longer i remember years ago MER used to have a spec cleaner stopped glass fogging up that was good stuff cant seem to see it now though ,

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As far as I know, unless the mirror is very very dirty, it is not worth the risk. You will be surprised how well even dirty mirrors perform and you likely won't notice any difference post cleaning.

I will defer to those more experienced than me though.


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I've only done my 12" mirror once but I have done previous scopes and I used the method set out in the 2nd half of this Sky & Telescope article:


Unless it's really dirty it's best not to clean.

As far as I know there is no overcoating material you can put on first surface coated optical mirrors to keep them clean and / or mist free. The aluminising should have been overcoated with a special protective coating by the manufacturer. I don't think it would be sensible to add any further coatings yourself - far to much risk of impacting the performance of the optics.

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this is the method and vid I use. To be honest, I've only done it the once as mirrors tend to handle quite a lot of dust build-up without any loss of image quality. If however there is something such as bird poo, pollen etc that may erode the surface of the mirror then by all means remove it :)

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There has been various methods mentioned here


I actually wonder if some one tried an anti fogging substance in a newtonian I recently cleaned. A very light finger touch left smears that wasn't down to grease on my fingers. The mirror in an LX90 was interesting as well as was the corrector. It's has improved significantly since I cleaned it.

What I think is important irrespective of method is to make sure things are very wet as this significantly reduces the chance of dust causing scratches. Using a blower bulb first helps too. Then as little as possible pressure. Sadly getting refractive optics very wet isn't a good idea at all as it may run into the cell the parts are held in.


One thing I will add is that there is all sorts of gunk kicking about in the atmosphere and it does settle on optics over time and it wont come off that easily. In some areas where optics are used they get cleaned every 12 months to ensure that they never get that dirty. Some optics need it more often  than that. The solution ideally used for this is nothing other than triple distilled water and some sort of wetting agent. I've no idea which one.



Edited by Ajohn
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