Please take a look at this picture. It shows a Soviet anti-aircraft battery team in action at Kursk in August 1943. I am curious to know more about the device that the soldier on the right is using.
From the looks of it, I imagine that it may be some sort of optical equipment that gives a stereoscopic view of distant targets (although that is a total guess). But, if I am right about that, does it work by the parallax principle? Given the relatively short distance between the two ends of the tube, is it even possible to exploit the parallax phenomenon? Bottom line is that I don’t really have a clue!
As the Wikipedia article notes, you do indeed get enough parallax from that distance to get a meaningful reading. The pentaprism they refer to bends the light path through a 90 degee angle, reardless of the angle of incidence (unlike , say, a right angle prism, in which the angle between the incoming and outgoing ray depends on the angle of incidence). Typically, there was a thick glass plate or another prism inside that you rotated to get the two images to coincide. The readout on the rotating knob gave you the range to target.
How far away parallax is good for depends both on the length of the baseline, and on the angular resolution you have available. These devices are presumably designed to maximize the angular resolution.
