What additional safety measures should be taken when observing with telescopes or binoculars?

Extreme caution is required. The lenses of telescopes and binoculars act as giant magnifying glasses that concentrate the Sun’s heat, which can cause instant and irreversible blindness. An approved solar filter must always be fitted to the front aperture of the instrument (where the light enters) and be securely fastened. Never use standard eclipse glasses to look through a telescope, as the concentrated heat will melt the glasses in a second. You can find all the detailed technical instructions here: How to observe eclipses (IGN)