Ocular Lens
Also: Eyepiece
The rear lens of a riflescope, the one you look through, focused to your individual eye using the diopter adjustment in the eyepiece.
The ocular lens is the glass at the back of a scope, nearest your eye, and it is the final element the image passes through on its way to your pupil. Where the objective lens at the front gathers light and forms the image, the ocular lens magnifies and presents that image along with the reticle. It sits inside the eyepiece, the part you bring up to your face when you mount the rifle.
Getting the most from the ocular lens depends on two things working together: the diopter setting, which sharpens the reticle for your particular vision, and proper eye relief, the distance your eye must sit behind the lens for a full, clear picture. A correctly adjusted eyepiece makes the reticle crisp and lets you find the image quickly under recoil and time pressure.