Dirty Primary Mirror

[Kedvenc]

I recently bought a Skywatch 200 and having a great time with it. First nights viewing was great. The second night was, hmmm, ok. I realised later when bringing the scope back in that everything was covered in dew including the primary. After leaving to dry I can see that the primary is basically quite grotty/dusty. Is this normal with a new scope or is it a result of the moisture? I'm not sure if the primary 'dewed up' outside or when I brought it into the (slightly) warmer room (its an out house with no heating). Will this grot have an effect on the performance?

I'm not intending to clean the mirror myself but considering taking it a local shop to let them clean it. Any advice is most welcome.

[MikeWilson]

I recently bought a Skywatch 200 and having a great time with it. First nights viewing was great. The second night was, hmmm, ok. I realised later when bringing the scope back in that everything was covered in dew including the primary. After leaving to dry I can see that the primary is basically quite grotty/dusty. Is this normal with a new scope or is it a result of the moisture? I'm not sure if the primary 'dewed up' outside or when I brought it into the (slightly) warmer room (its an out house with no heating). Will this grot have an effect on the performance?

I'm not intending to clean the mirror myself but considering taking it a local shop to let them clean it. Any advice is most welcome.

How grotty is grotty? Do you have a picture?

Primary mirrors can get quite grotty with dust and pollen and still deliver good views. Generally speaking though it's possible to give them a brief clean yourself without touching the delicately coated mirror surface. Use a bulb blower to blow off any obvious debris and wash with distilled water - there are instructions on the forum somewhere...

All the best,

Mike

[steppenwolf]

If this is a new instrument, it is extremely unlikely that there is anything serious on the mirror -looking at any mirror with direct illumination will make it look terrible so don't fall into that trap!

You'd need a fair amount of dust and 'grot' on a mirror to justify having it cleaned so I'd check out the dewing first and in particular see if the secondary mirror is dewing up.

[Kedvenc]

Thanks for the replies and advice. Next time out I will check for dew before coming inside to make sure. Skies are clearing here at the moment so hopefully tonight!

[Kevdan]

Hi,

Dew shouldn't cause any problems as it's "dirt" content is literally trace element as it is almost pure water, it should when dried off leave no traces or water marks, as Mike Wilson has said if needed take the mirror out and clean with distilled water, I think astronomy shed have a video on you tube on how to do this, and dont forget you'll have to collimate when you reasemble.

Kev.

[MikeWilson]

Kev's right - there's a YT video showing the process. It's not scary but don't use any harsh chemicals and a nice soak in some warm soapy water ought to clean almost all the gunk off the mirror.

But I'm still not sure you actually need to clean the mirror. Mirrors get rather dirty and still hold up well - whereas dew on the mirrors can stop an astro session with the cleanest of mirrors.

If you do have to take the mirror cell off, you might find that using a bulb blower gets rid of a layer of surface dust. I used to do this with my Newtonian every now and again to blow the large dust particles off.

[Kedvenc]

ok, thanks. Current plan is to not worry too much and see how it goes, hopefully tonight. I'm continually checking out the window these days to check the sky, gonna get neck problem if not careful.

[steppenwolf]

Current plan is to not worry too much and see how it goes,

Can't help but think that is the right course of action for now!