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Sometimes you can be trying to observe very faint or very small objects in the sky and it wouldn't pay to have these obscured or marred by a scratch or dust on the lenses.

I keep to good practices and make sure to replace the cap on the lenses when finished in order to stop dust buildup but inevitably it will get a little dusty and dirty, taking this into consideration:

What steps do I need to take to ensure that my lenses are kept in top condition?

Can I simply use a damp cloth or sponge and dab the lenses or should I use a softer material, like someone with glasses might have a softer lens cleaner?

Do I require a special cleaning fluid or can a good quality clean be done without any additional cleaning agents?

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  • $\begingroup$ Honestly, I would go with compressed air. Even with a damp cloth you can risk either scratching the surface, or you could leave residue as the moisture dries from the surface. I'll leave the answer to this question to a more knowledgable person. $\endgroup$
    – astromax
    Oct 25, 2013 at 0:12
  • $\begingroup$ I wouldn't use a compressed air canister as I'd be worried that it might play too rough. Get a photographic air blower bulb instead. $\endgroup$
    – MartinV
    Jul 24, 2017 at 11:01

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Clean your eyepieces in the same way you would clean a camera lens. An air blower, soft (i.e. camel hair) brush, lens tissue or microfibre cloth, and a solvent or alcohol will do the trick.

When I was an undergraduate I did some work with lasers and very expensive dielectric coated mirrors. The techniques here will show you how to carefully clean optics. Never completely wet your lens tissue or cloth. One drop on a lens tissue is usually enough, or a couple of drops on a microfibre cloth.

Essentially, you need to:

  1. Use a blower to blow off as much dust as you can.
  2. Then use a soft brush.
  3. Dampen a small square of lens tissue with pure alcohol or acetone (see warning below). Gently draw or wipe the tissue across the surface once, and then discard. Repeat if necessary.
  4. You may need to fog the lens with your breath to help remove water-soluble gunk.

Be insanely careful if you are using a solvent such as acetone. Although a good for cleaning optics, it's not very nice to paint and plastic so it should be a last resort for very stubborn marks well away from the edges of the lens (so you'll never touch the paint with it). Methyl or isopropyl alcohol are safer but less effective, or a generic lens cleaner from a camera store.

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  • $\begingroup$ ...and while damage to the paint done by acetone will be merely an insignificant matter of aesthetics, acetone-diluted paint smeared over the lens will be a problem. $\endgroup$
    – SF.
    Oct 25, 2013 at 10:40
  • $\begingroup$ Indeed that is even worse. Solvents are something to use only when you really know what you're doing and you are aware of the risks. $\endgroup$
    – Moriarty
    Oct 25, 2013 at 21:56

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