Parfocal Lens
A zoom lens that holds focus on the same subject as the focal length is changed.
In depth
True parfocal behaviour requires precise mechanical design and is largely confined to cine zooms, where a focus pull during a zoom must stay sharp. It also enables a useful technique: zoom in to focus critically, then zoom back out to compose, knowing focus will hold.
Examples in practice
A parfocal cine zoom focused at 100 mm stays sharp on the same actor when pulled back to 25 mm.