GB1484620A - Radiation sensing apparatus - Google Patents

Abstract

1484620 Automatic focusing HONEYWELL Inc 4 Dec 1974 [6 Dec 1973 (2)] 52359/74 Heading H4D An automatic focusing system, of the kind wherein the scene to be focused by main lens 43 is also directed by auxiliary lenses 27, 29 on to corresponding linear arrays 1, 3 of photodetector elements, lens 29 being moved in its plane until comparison of the outputs of corresponding ones of the elements in each array determines that the two images cast on the arrays are equal, the resultant position of lens 29 being indicative of the scene's range by triangulation, is calibrated for inequality of sensitivity of corresponding elements by intertuption of the two images by a diffuser 46 such that any inequalities in the images on the arrays are smoothed out and equal light falls on said corresponding elements. A calibrating signal (which should be zero) is then produced from the comparison of the outputs of said corresponding elements and is stored for correction of the normal comparison signals when the diffuser 46 is removed. When the elements are photo-resistive, Fig. 1, corresponding elements in the two arrays, e.g. 5 and 13, are connected in series between a positive and a negative source 21, 23, with the junction points 21, 33, 35, 37 giving the difference between the elements outputs and the difference signals being fed to respective balancing circuits 32, 34, 36, 38 which store the calibration signals produced from each element pair with the diffuser in position and subsequently subtract same from the difference signals. The resulting calibrated difference signals are summed in signal processor detector 39 (see Fig. 2) to give a focus adjusting signal F for control of the motor 41 driving the ancillary lens 29 and the main lens 43. When the elements are photovoltaic, all the elements are connected to ground to one side and corresponding elements have their other terminals fed to difference amplifiers, Fig. 5 (not shown). The storage of the calibration signal may use a simple long time constant RC circuit, Fig 3 (not shown) or the signal may be fed to the capacitor via a switch, e.g. an F.E.T., closed only during the calibration (Fig. 4, not shown).