Keep them capped and in a case, keep eyelashes and fingers off the eye lens, and let a dewed eyepiece dry before it goes back in a closed box. The eye lens is the surface that gets touched, and it is the one that actually affects the view.
Eyepieces are the accessories most handled and least protected, and both facts show at resale.
The surface that matters
The eye lens. It sits closest to the eye, gets touched by eyelashes, and collects the moisture from a breath on a cold night. A smear there scatters light exactly where contrast is most needed.
Between sessions
Caps on both ends and a case with dividers. Loose eyepieces in a coat pocket collect lint and scratches, and a case is a small purchase beside what it protects.
After a damp night
Leave them uncapped in a dry room until they are dry, then cap and box them. A dewed eyepiece sealed in a case grows the film that everyone later tries to clean off.
The mechanical detail
Insist on compression-ring clamping in diagonals and focusers. Thumbscrew marks are permanent, and a set of scored barrels is the first thing a second-hand buyer notices.
The questions that keep arriving
Why does the eye lens matter more than the field lens?
Because it is close to the eye and to the image, so anything on it — a smear from an eyelash, a fingerprint — scatters light right where it is least welcome. Dust deeper inside the eyepiece matters far less.
What marks a barrel?
Thumbscrews. A diagonal or a focuser that clamps with a bare screw scores the barrel of every eyepiece it holds, permanently and visibly. A compression ring grips without marking.
Last reviewed 17 September 2026