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A 50mm right-angle finderscope mounted on a 150mm telescope. Tour guide points out the double Finderscope on the 24.5 inch Cassegrain Telescope at the Goldendale Observatory State Park . A finderscope is an accessory sighting device used in astronomy and stargazing , typically a small auxiliary refracting telescope / monocular mounted ...
This means that, for a triangle with a given angle, the ratio of opposite side length to adjacent side length (tangent [broken anchor]) is constant. By using a reticle with marks of a known angular spacing, the principle of similar triangles can be used to find either the distance to objects of known size or the size of objects at a known distance.
In 1881, the British Royal Artillery adopted the depression range finder, which had been developed by Captain H.S.S. Watkin for use by coastal artillery. It used the measurement of the angle of depression from the observer, sited on a high vantage point, to the waterline of the target vessel. [5]
Two sides and an angle not included between them (SSA), if the side length adjacent to the angle is shorter than the other side length. A side and the two angles adjacent to it (ASA) A side, the angle opposite to it and an angle adjacent to it (AAS). For all cases in the plane, at least one of the side lengths must be specified.
The observer would first use this device to measure the angular width of the target. Knowing the angular width of the target, the range to the target, and the known length of that ship class, the angle on the bow of the target can be computed using equations shown in Figure 2. Human observers were required to determine the angle on the bow.
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The position of the lenses A and B are known, and the angle of the lenses α and/or β is set by the operator so that both are aimed at the target. Because the distance between A and B on a coincidence rangefinder is typically fixed, once the angle is set correctly the operator need only read the range from the scale.
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