Abstract: The presence of an operating helicopter within a given field of view is remotely and passively monitored by optically imaging the field of view at a focal surface, using an infrared detector to produce an electrical signal. The electrical signal is filtered with a narrow pass-band having a center frequency which is adjustable over a range which spans the respective modulation frequencies of characteristic infrared radiation emitted by the rotating blades of each of a plurality of helicopters of different type. Provision is made to indicate such component of the electrical signal as survives the filtering step.

Abstract: The invention contemplates circuit arrangements to protect the target of an image-producing tube from injuriously high local current densities, wherein detector means is responsive to produce an electrical pulse at onset of an unacceptably high local-illumination intensity condition at the cathode. The target-cathode excitation circuit includes switch means with a resistance-changing characteristic, and so connected to respond to the electrical pulse as to rapidly reduce electron flow between the cathode and target of the tube, upon occurrence of such electrical pulse output.

Abstract: The invention contemplates improvement in the interpretability of heat-detection data, resulting from scanning a field. One or more heat-detecting devices are caused to scan the field and to create light modulation, superposed on a monitoring display of the field, the monitoring display being the product of observing the field in a band (e.g. visible light) other than that of the scanned heat response. The result is to superpose on the monitoring display brightened light modulations in accordance with heat sources encountered in the course of heat scanning the same field.

Abstract: A device for binocular viewing of, for instance, fluorescent screens, image converters, and image intensifiers. Designed to be hand held, the device is light and compact. A single optical system of at least four lens elements provides the desired magnification. Behind the last element (in the direction of travel of the light from the object being viewed to the eyes of the person using the device) there are two rhombic prisms to spread the light beam to the two eyes of the user. In a preferred form, the prisms are adjustable to match the interpupillary distance of the user. At least one of the lens elements of the magnification system preferably has an aspherical surface.