Periscopic sight is a sight in which the objective lens is at a different height to the eyepiece(s), usually above.
Tank periscopic sights are mounted on the roof of the tank turret.
Until the advent of overhead top attack, the periscopic sight had a distinct advantage over the telescopic sight from the protection point of view, as it preserved the integrity of the turret frontal armour. However, to maintain the alignment of the periscopic sight with the gun, it is necessary to elevate and depress the line of sight, either by moving the sight itself or its top mirror, using a mechanical parallelogram linkage or sensors. The offset between the gun and the sight produces a parallax error, but this can be compensated for by means of the fire control computer. When a parallelogram linkage is used, the accuracy of the system can be degraded if the vehicle is subjected to large changes in temperature.
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15.04.2013