Do reflectors have protective coating on the primary mirror?

[Planetarian]

I've got a SkyWatcher 130p, and just wondering if the primary mirror got any protection on top of the aluminium coating. As I know aluminium gets an oxide later on it's surface after a time. 

In case they coated it with an extra layer of some kind of protective material, then it will stay shiny for a long time. I hope this is the case. 

[discardedastro]

Just now, Planetarian said:

I've got a SkyWatcher 130p, and just wondering if the primary mirror got any protection on top of the aluminium coating. As I know aluminium gets an oxide later on it's surface after a time. 

In case they coated it with an extra layer of some kind of protective material, then it will stay shiny for a long time. I hope this is the case. 

They are coated, yes - this is actually why you must not touch the surface (outside of extremely careful and delicate wet (lubricated) cleaning, very very occasionally).

If the coating starts to go, the mirror surface itself can eventually degrade, until re-coating is the only way to resolve it (dissolving the aluminium coating off, and re-coating it in a vacuum chamber, a very specialist activity). Your 130P will last for years and years before it's at risk of that if looked after properly.

[johninderby]

From the Skywatcher website.

[Planetarian]

Thanks, that's good news. I'm gonna make sure my mirror stays clean but one day if it will be necessary to give it a wash i guess I'm just gonna need washing up liquid, some sterile cotton balls and distilled water to rinse it. 

[ScouseSpaceCadet]

2 minutes ago, Planetarian said:

Thanks, that's good news. I'm gonna make sure my mirror stays clean but one day if it will be necessary to give it a wash i guess I'm just gonna need washing up liquid, some sterile cotton balls and distilled water to rinse it. 

You shouldn't need to worry about mirror cleaning for years.  After use, leave the covers off and let the telescope dry naturally indoors, open end angled down a little, until everything looks visibly dry before putting the dust cover on and storing the tube.

During periods of inactivity, or waiting for it to cool, the same applies. Leave the dust cap in place and the telescope either level or angled open end down a touch.

Some dust, floral debris and a touch of bug splatter won't spoil the view. 😉

[NGC 1502]

As already mentioned most telescope mirrors have a protective coating over the aluminium, if properly done this will give a far longer life for the aluminium.

The overcoat is actually quite hard, although this must not allow us to take chances when cleaning becomes necessary. Lots of correct advice is around that dirty looking mirrors perform well.

The protective overcoat is invisible to the human eye.

Ed.

[Chris]

My father in law has used the same 8" reflector for 40+ years without either cleaning or recoating his mirror, well he might have blown on it once a decade perhaps. It's covered in all sorts but still puts up a lovely bright and sharp image so honestly you have nothing to worry about 

[Planetarian]

Thanks for the replies, I'm feeling more relaxed about the longevity of my telescope now. 

[RT65CB-SWL]

It used be known or had been said, that if you lived near coastal locations that mirrors would need coating more often; than those of inland locations due to the 'salty' atmosphere.

[discardedastro]

5 minutes ago, Philip R said:

It used be known or had been said, that if you lived near coastal locations that mirrors would need coating more often; than those of inland locations due to the 'salty' atmosphere.

This may well be true of mirrors without coatings, but silicon dioxide and friends do not react to saltwater. May well need cleaning more often, mind you, which might lead to quicker coating failure...

[Planetarian]

I'm at about 30 miles from the sea.

Edited September 27, 2020 by Planetarian