ZOOM LENS SYSTEM

WIPO Patent Application WO/2014/132864

A1

A zoom lens system suitable for use as a day/night lens for observation that is short in total length, maintains a high variable power ratio by having a long focal length on the long focus side, and can achieve excellent optical performance by favorably correcting chromatic aberration from the visible range to the near infrared range across the total zoom range. The zoom lens system has, in order from the object side, at least a first lens group with a positive refractive power and a second lens group with a negative refractive power, with the space between the first lens group and the second lens group increasing during changes in magnification from the short focal length end to the long focal length end, and is characterized in that the first lens group has at least one doublet in which a diffractive surface that satisfies conditional expression (1) and has a rotationally symmetric shape with respect to the optical axis is formed as an interior surface of at least one of the doublets, and in that the lens system satisfies conditional expression (2). Conditional expression (1) 130<|fD/RD|<10000 (fD>0) and conditional expression (2) 0.15