Eyepiece UltraFlat 18mm

The optical elements are treated with ultra-thin coatings. Among others, there are anti-reflective coatings for reducing, and dielectric coatings for increasing reflection.

This is the angle of aperture of an eyepiece.

The smaller the focal length of an eyepiece, the higher the magnification when used with a telescope.

Eyepieces with an ED element, as seen in apochromatic binoculars.