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Cleaning A Newtonian Mirror.

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During an observing session on Friday night, after the primary had dewed slightly I noticed the mirror covered in brown marks and finger prints.

This must have been done at the factory as the scope was brand new from Steve at Flo. (It was originally his and I don't think he ever used it.)

Whilst having a coffee at Flo's this morning I chatted to James about cleaning the mirror, he tried to dissuade me by saying, "Is there anything I can say to stop you taking that mirror out!"


So I had a few spare hours this afternoon and decided to have a go.

First of all let me say that it's not as daunting as you first think. However only remove the mirror if it's really dirty or really, really dusty.

The first thing you need to do is prepare the area. Make sure you have lot's of time and no distractions. take the phone off the hook and send the wife and kids to the zoo or something. Allow an hour for removal and washing of the mirror and allow the mirror to dry overnight in a fairly dust free environment.

Use quality tools....And make sure the screwdrivers and allen keys are the right type and fit correctly, you don't want a chewed allen bolt!


The first thing I did was to mark the orientation of the mirror cell using some masking tape and a pencil.


I removed the 4 allen bolts that secure the mirror cell...They are really small and easy to chew with the allen key.


After carefully lifting the mirror cell off it ventured to the worktop and placed on a tea towel.


Next I removed the retaining ring. The mirror is retained in the cell with six long screws, they were removed along with the three rubber bushes.



I placed some soft kitchen cloth in the bottom of the sink.


I had dificulty removing the mirror from the cell as it was glued in with silicone so in the end I washed the mirror in the cell.

Once the mirror is in the sink gently run the tap and allow the water to flow over the mirror.


Using pure cotton wool (From the chemist) I gently washed the surface of the mirror, I didn't use any soap or detergent. I changed the cotton wool every sweep of the mirror to avoid scratching and or re-contaminating the mirror.

Once I was happy I rinsed the mirror with distilled water to avoid water spots.

Once I was happy I placed the mirror on a tea towel to dry.


Once the mirror and cell were completely dry I replaced it into the OTA making sure I aligned the marks. A quick collimation and et voilà...Squeaky clean!

My OTA is a Schmidt Newtonian, but the principal for cleaning will be the same, removing it from the OTA may be a little different.

Hope you find this useful.


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Excellent (and confidence inspiring) mirror cleaning instructions Greg!

Just shows, it can be done - with the right preparation (having time completely on your own, with absolutely no distrations).



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Good, detailed procedure Greg :undecided:

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