Located or occurring outside the main focus or focal point, especially in optical or medical contexts.
From Latin 'extra' (outside) + 'focalis' (relating to a focus or hearth, from 'focus' meaning fireplace). The optical sense emerged in the 19th century when scientists studied light behavior outside focal points.
When you wear glasses, the extrafocal regions are the blurry areas around the edges—but new lens designs actually use this blur strategically to slow down myopia in children!
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