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Old 13-07-2020, 08:47 PM
bluesilver (Peter)
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bluesilver is offline
Join Date: Jul 2018
Location: Australia, Tasmania
Posts: 207
Dobsonian primary mirror cleaning

Hi, I had a strange issue tonight when observing the planets with my 16" Skywatcher dobsonian with goto.

Rolled the scope out about and hour and a half or so before nightfall, around 4 pm here, to get it acclimatised to the air as it cools.

As the night went on, i found that right in the centre of the eyepieces i was getting what looked like a slight fog issue, kind of like when your glasses fog up.
But it was right dead centre of the eye piece, Only noticed this when viewing the bright planets.

I thought i might have some issues with the eye piece internally fogging up, So swapped it out for another and same issue.
Got me thinking a bit, so i got a torch and had a look at the main mirror only to see that there was condensation / fog right around the centre of the mirror and then also right around the outside of the mirror,
The rest of the mirror appeared to be fine, forgot to take a look at the secondary.

The night was very cold and there was condensation all over the outside tube.

So i am thinking, do i need to clean my primary as i was getting that odd due/ fog on the primary but only around the outside and centre.
And if so, what is the best way to clean them?

Or is it just one of these things that happen?
I have fans for it, but in my error, didn't have them on.

Any advice is appreciated.
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