Transfocator
Varifocal lens - a device allowing to change the focal length over a wide range (zoom function). Lenses equipped with varifocal lenses are called varifocal lenses. The focal length can be changed manually or via servo control. Due to their high cost, varifocal lenses are used only in cases where it is necessary to quickly enlarge an image of a small detail (for example, personal identification)
Source: "Selection and Application of Television Surveillance Systems. Recommendations. Р 78.36.002-99"
(approved by the Ministry of Internal Affairs of Russia on 04.10.1996)