After one telescope has been adjusted, other telescopes, aiming circles and quadrants may be adjusted by merely measuring the site of some distant point. The other telescopes and guns, being in position near the adjusted telescope, are then made to read the proper site when laid upon the distant point.
FIELD ARTILLERY RANGE FINDER, 1 METER BASE
(Bausch & Lomb.)
The instrument and accessories consist of the range finder proper, the tripod mount, the tripod, the adjusting bar, the carrying-case and the storage box.
The optical parts of the range finder are embodied in a seamless, steel tube (A) covered with canvas and asbestos, to minimize the effects of the change of temperature. The eyepiece (B) is located in the center of the instrument and is equipped with a focusing device graduated in diopters. A soft rubber eye cap is furnished to protect the observer’s eye from shocks and stray light. A ray filter having two sets of glass is operated by a small lever (C) situated to the lower left of the eyepiece housing.
DIAGRAM TO ILLUSTRATE THE
GENERAL PRINCIPLE OF RANGE-FINDERS.
The objective openings on the end boxes are opened and closed by means of rotating shutters (D). Buffers (E) are provided on the ends as a protection against shocks.
The range finder is of the type known as the fixed base, invert, single coincidence. The magnifying power is 15; actual field of view 50 mils; shortest distance measurable 400 yards. The instrument weighs about 20 pounds. Under favorable conditions and with expert operators the average errors are:
| 1000 yds. | 5 yds. |
| 2000 yds. | 15 yds. |
| 3000 yds. | 30 yds. |
| 4000 yds. | 55 yds. |
| 5000 yds. | 90 yds. |
| 6000 yds. | 130 yds. |
| 7000 yds. | 175 yds. |
| 8000 yds. | 225 yds. |
In practical use under ordinary conditions and with average operators, the errors are three times as great.