MWIR Very Large Collimator
The Very Large Collimator was designed to project imagery from resistor arrays for MWIR cameras being tested in the Kinetic Kill Vehicle Hardware-in-the-Loop Simulation (KHILS) facility at AFRL, Eglin. In addition to resistor arrays, it can be used to project imagery from a number of different source types, such as LED arrays, and it can be used for device characterization of new projector technologies. The following is a list of the Collimator optical characteristics:
· FOV: 18 deg with FtanΘ mapping function
· Focal Length: 225 mm
· Image Diameter: 71.2 mm
· Spectral Band: 3 – 5 µm
The Collimator was tested by placing a black body with various types of targets at its image plane. A Telops MWIR Camera with a 50 mm focal length lens was used to capture the collimated beam. The resulting images of two targets are show below. They are diffraction limited with < 0.2% distortion.
The distortion was measured and quantified by placing a thermal wire grid target at the image plane of the Collimator.
The Collimator could be used as a long focal length lens by placing the Telops Camera sensor at the image plane. Several night images were captured of high voltage transformers, palm trees, and mountains several kilometers away.
Time sequence images were also captured. The figure below displays 3 groups of 4 image snaps from a video taken at 4 different exposure times ranging from 500 to 4000 micro-seconds. In the first sequence a face is seen viewing a hollow metal tube while a flame from a torch is being brought to it from the right side of the image. In the second sequence two of the exposure times have been shortened. The flame is just beginning to enter the tube (the face is outside the FOV during this sequence). The color green signifies areas of pixel saturation. In the final sequence the two exposure times have been increased again to their original durations. The flame is now aligned to the tube, which has begun to heat up. The face has returned behind the tube. Notice how the rate of saturation across the tube depends on the exposure time. Notice also that the face is visible at 4000 usec but not at 500 usec. The trade-off is saturation of the hot tube at 4000 usec, but with the ability to see the face. At 500 usec the temperature gradients across the tube can be detected, but not the face.
Another set of 3 groups of 4 time sequence images are shown below. In the first sequence a match is lit near a candle with a face behind it. In the second sequence the candle is lit. In the third sequence the face is replaced by a hand that approaches to light the candle from the side. The range of exposure times is increased to improve the visibility of the hand, but at a cost to saturating the flame.
