Mirror coatings - how quickly do they deteriorate?

[MortonH]

Realise there's no correct answer to this question because obviously it depends on the frequency of use, exposure to moisture, etc. but am wondering in very general terms how much reflectivity might be lost over time.

Reason I'm asking is that I'm currently looking for a 10" Dob. My previous Dob was 8" so I'm looking to increase the aperture. But if I buy a used 10" Dob that's had a few years of use, am I really buying 10" of aperture? Or would a brand new 8" show just as much?

Any thoughts?

Cheers

Morton

[GrahamL]

My 12" gso coating is approx 5+ years old
I used to live quite close to the beach and probably more often than I realised there was a fair bit of salty air floating around at times.

The coating is definately showing signs of time , but is still very much usable and in probably another 3/4 years would still be .

10 " scopes pop up now and then with minimal use , but still used;)but then your buying at a reduced price arn't you ?

good luck

[multiweb]

I'd say the wetter they get the sorter the life of the coating. If you manage to ventilate your primary and keep it reasonably dry it should last longer. I had to recoat my 5" newt after about 4 yrs of use. It did get out a lot though during that period and I did a lot imaging with it. The new coating has a quartz overcoat which is supposed to last a long long time. The original coating was from Celestron factory and I don't know what it was.