eyepiece

eyepiece — noun

1. the round glass part at the top of a telescope, microscope, binoculars, or other

1.nounB2
Definition

the round glass part at the top of a telescope, microscope, binoculars, or other optical instrument that you place your eye against to see an enlarged or clear image

Example

Xiu adjusted the eyepiece of her microscope to see the bacteria more clearly.

collocation: adjust the eyepiece

The telescope’s eyepiece had a small scratch, so the stars looked slightly blurry.

Common collocations
  • adjust the eyepiece
  • look through the eyepiece
  • eyepiece of a microscope
  • eyepiece of a telescope
  • clean the eyepiece
  • focus the eyepiece
Synonyms
  • ocular lens

    the formal technical term, more common in scientific writing than in everyday speech

  • eye lens

    describes the same part by function; less frequently used than 'eyepiece'

Antonyms
  • objective lens

    the lens at the opposite end of a microscope, closest to the specimen being viewed

Grammar Patterns

the eyepiece of [instrument]

Usage Note

Often paired with a specific instrument name in a prepositional phrase (e.g., 'eyepiece of the microscope'). The counterpart on the opposite end of a microscope is the objective lens.

Common Mistakes

❗ 'Look at the eyepiece' (when the intended meaning is looking through it). ✅ 'Look through the eyepiece.' — 'at' suggests examining the object itself; 'through' describes using it to see something else.

❗ 'Change the eyepiece of the telescope to a stronger lens' ✅ 'Replace the eyepiece with a stronger one.' — 'change [part] of [thing] to [thing]' sounds unnatural for optical components.

Synonym discussion

Sense: noun/1

Eyepiece is the everyday word for the glass part you look through on a microscope, telescope, or binoculars. Ocular lens is the more formal technical term, often found in scientific manuals and product specifications — it carries a more precise, academic tone. Eye lens is rarely used on its own; it usually appears as part of a compound description ('the eye lens assembly') in engineering contexts. In classroom science and hobbyist use, 'eyepiece' is the natural choice. For example, a teacher would say 'Look through the eyepiece,' not 'Look through the ocular lens.'

eyepiece ↗ocular lenseye lens

Common collocations

Nouns

Adverbs

Phrases

  • look through the eyepiece
  • adjust the eyepiece
  • clean the eyepiece

Prepositions

Etymology

Old EnglishOld FrenchEnglish

The word 'eyepiece' is a compound formed in English from 'eye' (from Old English ēage, meaning the organ of sight) and 'piece' (from Old French piece, meaning a part or portion). It was first used in the early 1800s as optical instruments became more common and people needed a specific name for the part placed near the eye.