diopter: meaning, definition, pronunciation and examples
C2Technical / Medical
Quick answer
What does “diopter” mean?
A unit of measurement of the optical power of a lens or curved mirror, equal to the reciprocal of the focal length in metres.
Audio
Pronunciation
Definition
Meaning and Definition
A unit of measurement of the optical power of a lens or curved mirror, equal to the reciprocal of the focal length in metres.
In broader scientific contexts, it can refer to an instrument for measuring angles, such as an alidade or a sighting device on a surveyor's compass. It also refers to a type of adjustable eyepiece on optical instruments like microscopes or telescopes.
Dialectal Variation
British vs American Usage
Differences
Spelling: 'dioptre' (UK) vs 'diopter' (US). The standard metric unit symbol 'D' is used identically in both variants.
Connotations
No difference in connotation, both are strictly technical terms.
Frequency
The term is used with equal technical frequency in both UK and US contexts within relevant fields.
Grammar
How to Use “diopter” in a Sentence
[Number] [positive/negative] dioptersa lens of [number] dioptersadjusted the diopter on [optical instrument]Vocabulary
Collocations
Examples
Examples of “diopter” in a Sentence
verb
British English
- You must dioptre the telescope's eyepiece before use.
- The technician dioptred the lens array for optimal focus.
American English
- You must diopter the rifle scope for your eyesight.
- The camera assistant dioptered the viewfinder for the director.
adverb
British English
- The lens was calibrated dioptrically.
- The scale is measured dioptrically.
American English
- The power was expressed dioptrically.
- The system is designed dioptrically.
adjective
British English
- The dioptric adjustment was precise.
- He made a dioptric measurement of the cornea.
American English
- The diopter adjustment knob is on the left.
- She calculated the diopter power needed.
Usage
Meaning in Context
Business
Rare. May appear in specifications for optical products.
Academic
Common in physics, optics, and ophthalmology research papers and textbooks.
Everyday
Virtually unused outside of contexts involving eyeglass prescriptions or camera lenses.
Technical
The primary domain of use. Essential in optometry, ophthalmology, photography, and optical engineering.
Vocabulary
Synonyms of “diopter”
Strong
Neutral
Weak
Vocabulary
Antonyms of “diopter”
Watch out
Common Mistakes When Using “diopter”
- Incorrect plural: 'dioptries' (correct: 'diopters/dioptres').
- Mispronunciation: /ˈdaɪəptər/ instead of /daɪˈɒptər/.
- Incorrect abbreviation: 'dpt' instead of the standard 'D'.
FAQ
Frequently Asked Questions
No, while common in eyeglass prescriptions, it is a general unit for the optical power of any lens or curved mirror, used in cameras, telescopes, microscopes, etc.
A negative diopter value indicates a diverging lens (concave), used to correct myopia (nearsightedness).
A positive diopter value indicates a converging lens (convex), used to correct hyperopia (farsightedness) or presbyopia.
The spelling: 'dioptre' in UK English and 'diopter' in US English. Pronunciation and meaning are identical.
A unit of measurement of the optical power of a lens or curved mirror, equal to the reciprocal of the focal length in metres.
Diopter is usually technical / medical in register.
Diopter: in British English it is pronounced /daɪˈɒptə(r)/, and in American English it is pronounced /daɪˈɑːptər/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “set the diopter”
- “dial in your diopter”
Learning
Memory Aids
Mnemonic
Think: DIOpter = DIstance OPtic meTER. It measures the focusing distance of an optic.
Conceptual Metaphor
POWER IS MEASURED IN DIOPTERS (e.g., 'a strong lens of +6 diopters').
Practice
Quiz
In which field is the term 'diopter' MOST commonly used?