zoom focus shift

Zoom focus shift (also: zoom-induced focus shift) is the name for the phenomenon that the effective focusing distance of a zoom lens changes when the lens’ focal length/angle of view is changed. Zoom focus shift happens with most zoom lenses and whether zoom focus shift occurs or not is the differentiating factor between parfocal zoom lenses (no to almost no zoom focus shift) and varifocal zoom lenses (has zoom focus shift).

Zoom focus shift should not be mixed up with (plain) focus shift, which is the shifting of effective focusing distance due to a change in aperture. See more on focus shift in the JAPB article on focus shift.

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