chapter 6, Refractive Infrared Zoom Lenses

Excerpt

6.1 Target Simulators

Considerable progress has been made in the development of infrared target simulators with zoom optics. One important application is in the realistic testing of advanced missiles. This can be achieved with an electro-optical system that operates in the 3- to 5-μm or 8- to 12-μm waveband and reproduces an object moving with respect to a sky background, as it is seen by an approaching missile with a FLIR. The radiance texture of both object and background are achieved by an infrared transparency, whose pixel level can be chosen from as many as 256 gray levels. An infrared zoom lens simulates the closing distance between the missile and the target. The block diagram of an example of a target simulator is presented in Fig. 6.1. The target scene generator, background scene generator, and flare scene generator combine to present a varying image of the target at the entrance aperture of the unit under test.

6.1.1 CI Systems

CI Systems of Agoura Hills, California, has been a leader in the realistic simulation of infrared scenes for testing of advanced missiles. This has been achieved by building a completely automatic PC-controlled electro-optical system which operates in the 3- to 5-μm waveband and reproduces an object moving with respect to a background. The radiance texture of both the object and background are achieved by an infrared transparency, whose pixel radiance can be chosen from 256 gray levels. In one implementation with a 10:1 magnification ratio, a modulated infrared image passes through an array of nine lens elements that make up the zoom optics. The focal length range is from 150 to 1500 mm. The beam that exits the zoom optics is a collimated image of the simulator target. An optical schematic of the zoom lens is presented in Fig. 6.2. Although depicted going left-to-right toward the focal plane, in reality the light proceeds in the reverse direction. In order to match the 75-mm entrance aperture of the rest of the simulator system, the zoom lens exit pupil is by design positioned 200 mm in front of the first lens of Group I. Group I forms a fixed intermediate image.