"A true zoom lens, also called a parfocal lens, maintains focus while changing the focal length. Varifocal lenses require refocusing after changing the focal length."
- Axis Communications Academy, Network Video Fundamentals, 2022
"Zoom lenses allow you to vary the focal length and keep the image in focus."
- Axis Lens Guide White Paper
References:
Axis Communications Academy, Network Video Fundamentals, 2022 (p. 33)
Axis Lens Guide White Paper