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<p>[QUOTE=&quot;springfld.arsenal, post: 114235, member: 54&quot;]My latest thoughts:</p><p><br /></p><p>Operation:&nbsp; User first sets the density filter wheel to the appropriate setting of the four filter glasses provided.&nbsp; The darkest filter allows direct observation of the sun with no discomfort.&nbsp; The variable-density filters only filter light entering the optical port facing directly to the user&#039;s right.&nbsp; The user adjusts each eyepiece separately for focus.</p><p><br /></p><p>User looks into the larger eyepiece to see a split image formed by two small telescopes of about 4-power magnification mirrored at objective end so their axes point directly to user&#039;s right and left respectively, through small round glass windows in either side of the device.&nbsp; The two small telescopes are articulated so their axes may be diverged within the range of -2 to +2 degrees to obtain image coincidence, and the exact angle read-off as described below.</p><p><br /></p><p>When the images from right and left telescopes are brought into coincidence by the user adjusting the divergence by turning the small black knob, the divergence angle may be read by the user through the smaller eyepiece.&nbsp; The divergence angle scale is graduated in minutes and is read where the black cursor line crosses the -2 to +2 degree scale.&nbsp; The scale and cursor are illuminated by light entering a small, round, frosted glass window in the front of the device, opposite the two eyepieces.&nbsp; The device has no provision for night-time illumination of the scale and cursor, which may mean it is only possible to use it during daytime.&nbsp; That fact may help narrow down the list of possible uses for this device.</p><p><br /></p><p>Conversely, if the user has a pre-calculated angle of divergence, he may set the angle on the scale, then looking through the large eyepiece, mark the time at which the two target objects&#039; images coincide.</p><p><br /></p><p>The most striking feature of the operation of this device, as opposed to most other military optics, is that it was designed only for optical targets on opposite sides of the user.&nbsp; Since it was probably designed for use aboard a warship or submarine, the use may involve at least one horizon and perhaps a celestial body at the time of day that it is within two degrees of the horizon.&nbsp; If this was the intended use, note that, for example, the device would could determine the angle between the rising sun to the east and the western horizon.&nbsp;&nbsp; Since eastern and western horizons viewed from a ship in open ocean would be at the same distance, in sextant-user terminology, the sun could be &quot;brought down&quot; to the horizon opposite to the one from which it was rising.&nbsp; The instrument would measure the same angle above the horizon when comparing eastern sun vs. western horizon, as it would if it could compare eastern sun vs. eastern horizon, given that the two observations were made at the same time and date.&nbsp; The device may have been invented to solve a chronic difficulty of observing the exact time of sunrise or sunset with a hazy horizon adjacent to the sun.&nbsp; The sun is only used here as an example; another celestial body&#039;s rising and setting may also figure into this.&nbsp; The device may have been developed for use by surfaced submarines where the observer is very close to the water and hazy horizons may have been more of a problem than aboard surface ships.[/QUOTE]</p><p><br /></p>

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