Zoom lens requiring manual refocusing after each focal length adjustment, as focus and zoom are mechanically independent.
Technical Details
Varifocal lenses use a three- or four-group lens system where the variator and compensator groups are moved independently. The mechanical construction requires separate focus and focal length rings that are not coupled. Modern servo motors allow zoom speeds from 0.5 to 120 seconds for the complete focal length range. Cinema variants typically offer 300° focus ring rotation and 90° zoom ring rotation for precise operation.
History & Development
The first varifocal lenses were developed by Zoomar Corporation in 1947 for US television, based on Frank Back's patents from 1932. Angenieux launched the legendary 12-120mm f/2.2 Type 12x12B in 1956, which remained the standard for 16mm documentaries for over two decades. Canon revolutionized the broadcast sector in 1976 with the J8x6 8mm-48mm, the first fully servo-controlled varifocal lens. Since the 1990s, varifocal systems have dominated the ENG (Electronic News Gathering) sector.
Practical Use in Film
Varifocal lenses are particularly suitable for documentaries and news, where rapid focal length changes are required without lens changes. Haskell Wexler extensively used the Angenieux 12-120mm for "Medium Cool" (1969) to capture spontaneous street scenes. In modern filmmaking, documentary directors like Errol Morris rely on varifocal lenses for interview situations, where discrete reframing is possible without interruption. The disadvantage lies in reduced optical quality compared to prime lenses and the necessity to refocus with every focal length change.
Comparison & Alternatives
True zoom lenses maintain constant sharpness across the entire focal length range but are more complex and expensive. Prime lens sets offer superior image quality but require frequent lens changes. Modern cine-varifocal lenses like the Angenieux Optimo 24-290mm combine varifocal mechanics with improved optical correction. In the high-end segment, true zoom systems are increasingly replacing varifocal designs, while the ENG and documentary sectors continue to rely on varifocal solutions.