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Cleaning Secondary Mirror


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I noticed this morning my secondary mirror is abit dirty (looks like finger prints!) what is the best way to clean it?

I'm this astro book I have, it says use pure alcohol, but I wouldn't know where to get that from?

I was thinking something like surgical spirit? Or is that too harsh?


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From what i have read the recomendation is awlays to not clean the mirror. In fact one of the books I have read says that only clean the mirror when it is so bad as to be unusable. The reason being you will likely destroy the mirror so you are not loosing by trying!!

If you MUST clean it I would get a bowl with warm de-ionised water (car accessory shops) and a drop or two of fairy liquid. Imerse the mirror and using some (surgical, no I dont know where to get it either! try the chemists?) cotton wool also imersed in the water, very gently wipe in one direction only once then discard and get a fresh bit for the next wipe.

But really I would reccomend leaving it well alone, if it aint broke dont fix it and all that.... :nono:

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I am guessing that (like me) you won't be able to leave alone so....

Genuine cotton wool and distilled water (unless in a soft-water area) with a tiny amount of washing-up liquid (the pure type without creams and waxes). Use sparingly, change the cotton wool regularly and be gentle.

Good luck :thumbleft:

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Maybe get a little puffer, (hand held squeezy thing found in camera shop for a couple of quid), to blow any fine particulate matter off first if you can so that you dont scratch across the mirror.

As everyone has said - be gentle.

Remember that you will have to go through recollimtion from a long way off afterwards and be careful that when you are removing it the tube is horizontal so that nothing drops down onto the primary.

Best advice is probably - leave it till it really needs it. Post a picture on it and let us vote - "yes or no"!

I am guessing that the more times you clean the mirror the quicker it will degrade - (A guess and correct me if i am wrong). Also, I read somewhere that alcohol based cleaner, (such as those that are fine for SCT corrector plates), can degrade the mirror rapidly.

Take care and good luck


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