Lens

google

ref

late 17th century: from Latin, ‘lentil’ (because of the similarity in shape).

wiktionary

ref

Borrowed from Latin lēns(“lentil”), in Medieval Latin later taking on the sense of "lens".

etymonline

ref

lens (n.)

1690s, "glass to regulate light rays," from Latin lens (genitive lentis) "a lentil," on analogy of the double-convex shape. See lentil. Anatomical use, of the eye part, from 1719. Lens-cap is from 1857.

In the vernacular of the photographer, anyone crowding to the front of a group, staring into the lens, or otherwise attracting attention to himself is known as a "lens louse." ["American Photography," vol. xl, 1946; the term dates from 1915]