Cleaning Primary Mirror

[shyam]

hi

i dusted the primary mirror with a soft brush also applied a bit water to the tip of the brush and cleaned the mirror, but i see some mild scratches on the mirror may be two on sides. Has this happend due to my dusting of Mirror. i had checked the brush and for any roughness, but found its a good brush. The point of concern are

1. was the process of dusting resulted in scrach

2. how do we maintain the serivice of mirror

3. How tough is the coating on the mirror, is it on the front side or back side of the glass

 

m worried please adivice

thanks

shyam menon

[ronin]

If you applied water with the cleaning I would primarily think that the "scratches" are actually smears of the dust. The water and dust will have formed a bit of a paste and that will have left streaks of dust on the surface.

For dust it is likely best to keep it all dry. You might find that a micro-fibre cloth and a good proper lens/mirror cleaner will remove what I suspect are the streaks that have been left. I have found when cleaning assorted items that cleaning the item is easy, it is getting rid of the smears and smudges left by the fluid takes longer. If you try this then take it easy.

Coatings should be fairly tough, SiO2, the problem is how uniform is it, as any pin-hole errors in it allows oxygen, the other easily attacked area is the edge of the mirror as the protective coating does not really "wrap" around. The aluminium beneath then corrodes fast with the oxygen.

 

[Cosmic Geoff]

Your primary mirror already has a big lump of secondary mirror in front of it blocking part of the light. Think of this anytime you are tempted to clean off specks of dust.  I think you have just found why it is better to leave well alone unless the mirror is so dusty it is hard to see your face in it.

As the previous poster says, it can be difficult to get rid of all the streaks left by wet cleaning.

The coatings are reasonably robust and should not be damaged by cautious brushing, or washing with distilled water or safe cleaning fluids. But scrubbing off gritty dust with a dry cloth could cause permanent damage.   Under normal conditions, little dust collects if the tube is kept capped except when observing. 

[John]

You should really blow all loose material off the mirror with a manually operated puffer (not a compressed container) without touching the surface of the mirror.

I doubt the small scratches will affect the performance of the mirror though.

 

[shyam]

The scratches as mentioned is seen only when i use a torch light beamed to the mirror or else not visible.. as mentioned it could be minute smears left due to water and dust..

[Ricochet]

For future reference this video shows how to clean a telescope mirror. https://www.youtube.com/watch?v=8TObET2F-EA