Bifocal
by-FOH-kuhl
/baɪˈfoʊ.kəl/
Having two focal lengths, typically featuring one section for distance vision and another for close viewing.
Usually describes lenses that assist people who require vision correction for both distance and reading.
The story behind the word. Combines Latin 'bi-' (two) with 'focus' (hearth/fireplace, later adopted in optics for converging light points). Benjamin Franklin popularized split lenses in the 1780s so he could observe both near objects and distant rooms.
Word relationships
- dual-focus lens: Descriptive synonym highlighting the two focal areas.
- monofocal: Having only one single focus point.
Commonly confused with
- Trifocal: Trifocals feature three focal zones (distance, intermediate, near), whereas bifocals feature two.
Word family
- bifocals (noun): Eyeglasses with bifocal lenses.
Collocations
- bifocal glasses
- bifocal lenses
- wear bifocals
Example sentences
- "Benjamin Franklin is widely credited with inventing bifocal lenses to avoid switching between two pairs of glasses." Eyewear selection
Memory hook
BI = two, FOCAL = focus points; two focus areas in one glass. Two focal zones.
When not to use
Do not confuse with progressive lenses, which transition seamlessly without a visible dividing line.
Fun facts
- Benjamin Franklin called his invention 'double spectacles' long before the word bifocal was coined.
Related words
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