Eyecup

A: The eyecup is the extendable rubber or plastic tube (or shield) that surrounds the eyepiece at the viewing end. It may be extended outward and is used to set eye relief.

For those who do not wear eyeglasses, simply back out (extend) the eyecup until the full field of view is visible in the eyepiece. Eyeglass wearers do not extend the eyecup. As is, PENTAX eyepieces offer sufficient eye relief for most users.

An eyecup offers the added benefit of shielding the eye from unwanted light entering from the periphery of the eyepiece.