What is a parfocal lens?
A parfocal lens maintains focus as you zoom in or out. Once you focus on a subject, the focus stays sharp whether you zoom wide or telephoto. Most photo zoom lenses are NOT parfocal — they lose focus when you zoom, requiring refocusing.
Why parfocal matters for video
In filmmaking, a zoom during a shot is a deliberate creative choice — the slow reveal, the dramatic push-in. If the lens loses focus during the zoom, the shot is ruined.
Cinema zoom lenses are designed to be parfocal. You focus at any focal length and focus holds across the entire zoom range.
Photo zoom lenses are designed for photographers who refocus after zooming or rely on continuous AF. The slight focus shift is irrelevant because you refocus before each shot.
Parfocal vs varifocal
Parfocal: Focus stays locked during zoom. Standard in cinema lenses. Rare in photo lenses.
Varifocal: Focus shifts as you zoom. Standard in photo lenses. Requires refocusing after zooming.
Some photo zooms are nearly parfocal — the shift is small enough to be handled by continuous autofocus. Modern tracking AF helps compensate.
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Do you need a parfocal lens?
If you shoot video with intentional zoom moves during recording — yes, parfocal is important.
If you use zooms primarily to set framing then shoot, parfocal does not matter because you refocus after zooming anyway.
True parfocal cinema lenses are significantly more expensive. On a budget, use photo zooms with continuous autofocus — modern AF tracking compensates well enough for most use cases.
If you need parfocal behavior on a budget, test your photo zoom for focus shift. Some lenses, especially at longer focal lengths, hold focus surprisingly well during zoom.