MKS Instruments has developed a lightweight, compact, continuous zoom lens designed specifically for thermal cameras on UAVs, writes Nick Flaherty.

The Ophir FoldIR 25-275 mm f/5.5 MWIR continuous zoom lens is designed for the latest cooled 15 μm VGA thermal detectors. It uses a double folded optics design developed by MKS that shortens the optical path. This significantly reduces the length of the lens, and minimises the overall size and weight of the optical system.

The lens has dimensions of 107 x 101.5 x 96 mm (including the IR detector) and a net weight of 302 g (or 360 g including the detector).

It provides long-range detection capability of over 14.5 km and a sharp image across the entire field-of-view with continuous zoom. This allows the optics to be mounted on a 5 in (127 mm) aerial gimble.

The folded optics provide a long optical path but also reduce sensitivity to tolerances using fewer optical elements. It maintains sharp focus over the entire zoom range, allowing detection, recognition and identification (DRI).

The DRI range reflects the maximum range at which an object can be either detected, recognised or identified based solely on geometrical parameters: the target size, distance, lens focal length and camera detector pixel size. Signal level, detector sensitivity, atmospheric conditions and other factors are not considered.

Detection of an object with two pixels is possible at 14.5 km, recognition can be achieved with 8 pixels at 5.6 km and identification of a specific object can be realised using 12.8 pixels at 3.4 km.

The mechanical and electrical interface provides for easy integration into camera systems.