noun
eyepiece; ocular lens
The lens or lens group closest to the eye in an optical instrument such as a microscope, telescope, or binoculars.
顕微鏡の接眼レンズをのぞいてみた。
I looked through the eyepiece of the microscope.
対物レンズ is the objective lens (closest to the object), while 接眼レンズ is the eyepiece (closest to the eye).
Compound of 接眼 (setsugan, 'eye-connecting') and レンズ (renzu, 'lens').