Blow the loose dust off first, never wipe it in. Then, only if something is actually on the glass, follow the cleaning method the maker publishes for that coating — and clean far less often than instinct suggests.
The eye lens is the surface that matters, because it is close to the image and it is the one that gets touched.
Remove what is loose, first
A blower — not breath, which deposits moisture. Anything that will lift off without contact should lift off before anything makes contact.
Decide whether to go further
Look at the glass under a light. Dust scattered across it is costing almost nothing. A dried film from dew, a fingerprint or sap is genuinely scattering light, and is worth removing.
Follow the maker, not a general rule
Coatings differ, and manufacturers publish cleaning guidance for their own. That guidance is what to follow; this page reports that it exists rather than replacing it.
Prevent instead
Caps on both ends, a case with dividers, and letting a dewed eyepiece dry in a warm dry room before it is boxed. Most of what people clean off eyepieces was sealed in by capping them wet.
The questions that keep arriving
What makes cleaning risky?
A particle dragged across a coating scratches it, and the scratch is permanent where the dust was not. Removing the loose material before anything touches the glass is most of the technique.
How often is too often?
More often than once a season is usually too often. Dust costs a negligible amount of contrast; each cleaning carries a small permanent risk.
Last reviewed 17 September 2026