focal length
US /ˈfoʊ.kəl ˌleŋθ/
UK /ˈfoʊ.kəl ˌleŋθ/

1.
distance focale
the distance from the center of a lens or curved mirror to its focal point
:
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Adjusting the focal length changes the magnification of the image.
L'ajustement de la distance focale modifie le grossissement de l'image.
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A longer focal length results in a narrower field of view.
Une distance focale plus longue entraîne un champ de vision plus étroit.