Fungus ?

[banjaxed]

I have just been looking at my 8” skywatcher Dob and noticed some spots on the primary mirror, could it be fungus or just dust marks, looks like small patches of condensation to me. It is kept in my garage which is dry but not heated and I always keep the lens cover on.

[Ruud]

If you google for 'fungus on mirror' and you find that the images you get resemble what you see, then indeed, you probably got some fungus growing on your mirror.

Keeping a mirror in a garage is probably a bad idea. Still, clean the mirror with a disinfecting agent (alcohol and propanol work - the two active ingredients of Baader's cleaning liquid). The spots may improve a bit and at least won't keep growing.

After that, keep your mirror in a dry place and also avoid places that have a combination of (occasional) large temperature drops  combined with (occasional) high humidity. It's also a good idea to use a hair dryer to warm up your lens, corrector plate or mirror after bringing it in.

[banjaxed]

17 minutes ago, Ruud said:

If you google for 'fungus on mirror' and you find that the images you get resemble what you see, then indeed, you probably got some fungus growing on your mirror.

Keeping a mirror in a garage is probably a bad idea. Still, clean the mirror with a disinfecting agent (alcohol and propanol work - the two active ingredients of Baader's cleaning liquid). The spots may improve a bit and at least won't keep growing.

After that, keep your mirror in a dry place and also avoid places that have a combination of (occasional) large temperature drops  combined with (occasional) high humidity. It's also a good idea to use a hair dryer to warm up your lens, corrector plate or mirror after bringing it in.

Thank you for your information Ruud, I will check it out.

[banjaxed]

Did my first mirror clean today and fortunately it did not appear to be fungus as the marks cleaned off very easily. It turned out to be a lot easier than expected which is probably a first for me.