Abstract

A fixed-reticle stereoscopic range-finding sight, incorporating a reticle in which the elements were distributed in depth and elevation to simulate a trajectory, was evaluated in relation to an optically equal wandermark stereoscopic range finder. Data were obtained on the ranging sensitivity of experienced and naive observers with the two instruments and on the influence of the design of the ballistic reticle upon the observed range of the targets. The primary data obtained with the range-finding sight were in mils of elevation. The primary data obtained with the wandermark range finder were in seconds of arc of convergence. Mathematical transformations were used to reduce the elevation data to equivalent seconds of arc of vergence for purposes of comparison. The problem of repeated measures resulting from the fact that the reticle of the range-finding sight was an in-view range scale was met through the use of optical range adjustment.

For the targets employed in this study, standard deviation sensitivity in parallactic angle for experienced observers with the range-finding sight was five and three times poorer than that obtained for these observers with the wandermark range finder. For naive observers the relative sensitivities were in a ratio of four to one and one to one. The reticle of the range-finding sight as designed required an increasingly more negative internal corrector adjustment with increasing range. This tendency was attributed to the use of reticle elements of constant retinal subtense.

© 1956 Optical Society of America

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