13 replies to this topic

[stars-Dust]

clean, remove or apply new coat to the small mirror of the telescope

 

 

 

[Jon Isaacs]

I would start by cleaning it using this method:

 

https://youtu.be/9Y8...fa6pSaO9luiTxc8

 

Jon

[Tony Flanders]

The one time my secondary mirror got really dirty -- for reasons to embarrassing to describe here -- I cleaned it with acetone, on the advice of the manufacturer (Rick Singmaster). It's an amazing solvent, but toxic, so use gloves and reasonable caution.

[SeattleScott]

If it is dirt it might clean off. If it is rust, the coating is failing. Nobody recoats small mirrors, because it would cost 10x what the telescope is worth.

So yeah you can try to clean it and hope for the best. If that doesn’t work, you can continue to use the scope, understanding that performance is significantly degraded.

[stars-Dust]

If it is dirt it might clean off. If it is rust, the coating is failing. Nobody recoats small mirrors, because it would cost 10x what the telescope is worth.

So yeah you can try to clean it and hope for the best. If that doesn’t work, you can continue to use the scope, understanding that performance is significantly degraded.

Unfortunately it is not dirt/dust

 

most likely it is silver oxide. I am also suspecting fungus.

 

Thanks everyone

[apfever]

Clean first, you never know. It looks like corrosion spots but maybe not. It might work surprising well for the time being if the rest of the coating cleans up OK and only leaves the nice round dark dots. 

[SeattleScott]

Fungus can be cleaned but often damages the surface below. Either way, likely the mirror is permanently damaged. It will still work, but the view won’t be as bright as with a new scope.

[jragsdale]

Unfortunately it is not dirt/dust

 

most likely it is silver oxide. I am also suspecting fungus.

 

Thanks everyone

What is the size of the secondary? What scope is it from?

[stars-Dust]

What is the size of the secondary? What scope is it from?

About 3.5" (9cm)

[Oldfracguy]

You can buy a new one later this month:

 

https://agenaastro.c...rror-88-mm.html

[Bill Weir]

About 3.5" (9cm)

In which direction? Narrow axis or long?

 

Bill

[jragsdale]

In which direction? Narrow axis or long?

 

Bill

I think it's for an SCT.

[stars-Dust]

In which direction? Narrow axis or long?

 

Bill

It is the same scope as the one in this thread

 

the prime/large mirror at the observer side  while the small mirror we talking about is at the sky side .

 

the small mirror is reflecting the prism back inside a narrow tube located at the centre of the large mirror

 

https://www.cloudyni...meade-2080-sct/

[Oldfracguy]

It is the same scope as the one in this thread

 

the prime/large mirror at the observer side  while the small mirror we talking about is at the sky side .

 

the small mirror is reflecting the prism back inside a narrow tube located at the centre of the large mirror

 

https://www.cloudyni...meade-2080-sct/

I was just going to say that if the mirror was from an SCT it would either be from a C9.25 or a C11, but the secondary mirror on the C9.25 is a little smaller, and the one on the C11 is a little larger.  I then figured it might probably be a Meade SCT, and so it is.