Parfocal
The term parfocal describes an optical property of zoom lenses .
Zoom lenses whose focus remains the same while zooming, namely while changing the focal length , are referred to as parfocal lenses.
A parfocal lens allows video cameras to zoom in and out while recording without having to focus.
A parfocal lens enables photo cameras and video cameras to focus more precisely by focusing with the largest focal length and then zooming (with constant focus) on the desired larger image section.
Most commercially available interchangeable zoom lenses are parfocal lenses.
Lenses with a changeable focal length that are not parfocal lenses are known in technical terms as varifocal lenses. In colloquial language and in advertising, such lenses are also often referred to as zoom lenses.
Interchangeable variofocus lenses were manufactured before 1980 and did not play an important role. Built-in lenses that are zoomed and focused by an electric motor can be variofocus lenses. However, this feature should remain hidden from the user.