COMPARATIVE EVALUATION OF POCKET STEREOSCOPES.

The 12 stereoscopes used in this study were sufficient to perform the evaluation and reach conclusions on many of the characteristics. This evaluation of stereoscopes did not cover all the available instruments, although a search was made to try to obtain as many as possible to be included in the tests. If the stereoscope is moved over the stereo model so that the viewer is looking through the center of the lenses, all of the instruments tested have sufficient resolution. If, on the other hand, the stereoscope is placed in one position and the eye moved to look at images near the edge of the field of view, only one brand of stereoscopes approach an acceptable quality. For actual use in the interpretation of stereo pairs of aerial photographs, it is important that the resolution of the lens does not fall below the resolution of the eye. Each stereoscope had its good and bad points with respect to each of the factors other than lens quality, including rigidity, weight, size, the ease with which it may be set up for operation and put away, and its susceptability to wear at critical points. In most cases, simple low-cost modifications could make the poorer stereoscopes much better to use. The particular stereoscope to be used depends largely on the desires to the user. Author