mechanical assembly no relation prime lens
A zoom lens is a mechanical assembly of lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed-focal-length (FFL) lens (see prime lens).A true zoom lens (or optical zoom lens), also called a parfocal lens, is one that maintains focus when its focal length changes. Most consumer zoom lenses do not maintain perfect focus, but are still parfocal designs. Most camera phones that are advertised as having optical zoom actually use a few cameras of different but fixed focal length, combined with digital zoom to make a hybrid system.
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