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Glass cleaning


chn
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Hi

I dusted the scope off last night and when I looked at the end I can see a brownish mark on it, looks like some sort of liquid thats dried on the inside of the glass. The lense itself is 90mm in diameter and the mark is about the size of a 1 pence piece.

Whats the recommended process for cleaning this?

The scope is a Meade Bresser Messier R-90

Edited by chn
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If the mark is between the lens elements, then I'd leave it be. If you dismantle

the lens elements and cell, it all has to go back exactly oriented as originaly,

not easy to do.

If it is on the surface of the rear element and you can get at it without disasembly

of the elements/cell, then on most refractors the cell assembly unscrews as a unit,

allowing you to clean that innermost surface. I'd put some tape on the cell and tube,

with adjacent pencil marks, so that when you replace, it will screw on exactly as

originally.

I'd use isopropyl alcohol (good chemist) and a microfibre cloth (Jessops or similar)

plus great care !

Please be cautious, whatever action you take !

Regards, Ed.

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Thanks for the advice, I thought it wouldn't be easy.

I'm really not familiar with the technical terms of the scope, so not sure about lense elements and cells? Excuse my ignorance but as I look down the scope from the wrong end, it looks as though the mark is on the inside of the objective lense?

I can get some isopropyl from the local chemist I hope.

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I think what Ed says about the inside means the surface between glass elements in a doublet or triplet. If you look at your scope from the focuser end, that surface facing the inside of your scope is still consider the outside of the lens cell.

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Hi.

Adding to Ed & Keith's good advice.

An alternative cleaner to consider is 'Baader Wonder Fluid'.

Terrible name but a good product.

Look at FLO for a package deal on the cleaner and a good cloth.

It is not as aggressive as isopropanol (IPA) but still effective.

The IPA will rapidly move grease out of screw threads, fingers, focussers and anything it touches, then leave it behind where the IPA evaporates.

So IPA with care is fine, but if you are messy, it can leave a mess.

Whatever you use. Work in a warm comfortable place - the house. Solvents take an age to dry off when its freezing!

Hope this helps.

David.

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I think what Ed says about the inside means the surface between glass elements in a doublet or triplet. If you look at your scope from the focuser end, that surface facing the inside of your scope is still consider the outside of the lens cell.

Yes, the quote is what I meant, sorry I wasn't clearer.

The lens elements are the separate bits of glass, there will be two

in your refractor. The cell is the machined unit that contain the

glass elements, and usually screws onto the main telescope tube.

Hope this helps. If not, please come back for more clarification.

Best regards, Ed.

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