If you observe during a night when the temperature and humidity are right for condensation to form, sometimes you’ll notice it on your eyepieces (or telescope optics) at the end of your session. The best way to avoid any ill effects from condensation is to leave your optics uncovered when you bring them inside. That is, don’t put lens caps on eyepieces or tube caps on scopes. If you leave them uncovered for even a few hours, the condensation will evaporate and you won’t have any problems. (The same holds true for cameras and their lenses.) Be sure to cover them when they’re dry — the next morning will be fine — so you also don’t have issues with dust.
Michael E. Bakich