FIELD GLASSES AND TELESCOPES ISSUED BY THE SIGNAL CORPS.
The Signal Corps issues four standard field glasses, viz, Type A, Type B, Type C, Type D.
Field glasses issued by the Signal Corps are not supplied for the personal use of an officer and will not be used in lieu of the officer's personal field glass prescribed by paragraph 97, General Orders, 169, War Department, 1907 (Par. 1, G. O. 16, War Dept., 1910).
Under paragraph 1582, Army Regulations, as amended by paragraph I, General Orders, No. 207, War Department, October 16, 1909, the Signal Corps will sell field glasses to officers of the army for their personal use.
Application for the purchase of field glasses should be addressed to the Chief Signal Officer of the Army, Washington, D. C., inclosing post-office money order or check on the Treasurer or Assistant Treasurer of the United States for the amount, payable to the Disbursing Officer, Signal Corps, and Signal Corps Form No. 240 accomplished in duplicate.
The Government does not pay transportation charges for the shipment of articles sold to officers. Field glasses are sent from the Signal Corps General Supply Depot, Fort Wood, New York Harbor, by express, charges collect, unless purchase request is accompanied by funds so that field glasses may be sent by registered mail. Forwarding by registered mail is somewhat cheaper than by express, and the amount of postage required is 40 cents for Type D glass, 46 cents for Types A and B, and 74 cents for Type C. Express charges depend upon the distance from New York.
The Signal Corps has purchased many samples of field glasses from various manufacturers with a view of testing their suitability for the military service. These samples may be examined by officers of the army at the signal office in Washington. Among these samples there are many excellent glasses especially suitable for the military service, but the higher grades are too expensive for general issue to line organizations in large quantities. Officers desiring an especially fine field glass should inspect the samples referred to; these, however, are not for sale by the Government, but information will be supplied concerning dealers and cost.
No advice or fixed rule can be stated as to what constitutes the most suitable characteristics of a field glass. No single field glass can furnish maximum results under all conditions on account of varying conditions of the atmosphere.
A high-power glass is unsuitable for use at night, hazy atmosphere, or for use of a mounted man where the glass can not be rested against a firm support. A low-power glass with large object lens to permit as much light as possible is a necessary condition for use at night. The double power glass which is issued as a part of the visual signaling outfits was designed for the military service as a compromise for conflicting conditions.
A brief description of the field glasses issued by the Signal Corps, together with the cost of the same, is given below.
Type A:
This glass is the current result of the efforts of the Signal Corps to provide a field glass that will meet the greatest variety of conditions, and insure efficient service to the greatest number of military observers. It is really two glasses in one—a day glass of medium power, and a night glass of low power.
Fig. 31.—Type A. Showing the field glass and case with sling cord, shoulder straps, belt loops, and compass
It is to be clearly understood that while this glass is considered superior for moderate ranges, it does not replace, under special conditions, for long ranges, either the porro prism glass or the telescope.
When held as shown in [figure 32] with the tubes drawn out about 1 inch to secure proper focus, the glass has a power of about 5.6 diameters, and a field of about 5.4 degrees.
Fig. 32—Signal Corps field glass, Type A.
If the glass is turned into the position shown in figure 33, the small plus lenses, just in front of the eye pieces, drop automatically into position and reduce the power to 3.8 diameters, and increase the field to 8.3 degrees. This position requires a different adjustment, the tubes being drawn out about one-third of an inch to get the proper focus. It will be observed in the illustrations that the rear bar of the frame is not only lettered to indicate which power is being used, but the bar itself is shaped with a hump on one side, and hollowed on the other. When the hump is up, the low power is in use. This is to facilitate adjustment in the dark.
The action of the small automatic lenses is free and positive. Neither the eyepieces nor the sections containing the small lenses should be unscrewed, except in case of necessity, and then not by unskilled hands.
Fig. 33.—Signal Corps field glass, Type A.
The frame, of aluminum and brass, is composite, to give lightness and strength; and while it is constructed to withstand the rough handling of field service, no field glass is proof against careless or wanton treatment. The tubes are covered with tan leather, and a round sling cord, braided from four strands of pliable tan leather, is fastened by snaps to eyes in the frame.
The case is of tan calfskin, provided with shoulder strap, and has an efficient small compass set into the cover. Two loops are sewed to the back of the case so that it may be worn on a belt.
The glass, complete with case, cord, and straps, weighs 21.5 ounces.
Two of these glasses are issued to each company of infantry and coast artillery, Philippine Scouts, and Signal Corps, and to each troop of cavalry for use in instruction in visual signaling. Below is a brief description of the type A glass.
Magnification, 3½ and 5½ diameters; Galilean type; object lens, 1½ inches; tan leather finish; tan leather carrying case with compass; weight of glass, complete, with case, cord, and strap, 25 ounces. At a distance of 1,000 yards the field of view includes a diameter of 123 yards for the 3½ power, and 73 yards for the 5½ power. Length of glass closed, 4 inches. This glass is issued as a part of the visual signaling kit to each company of infantry, coast artillery, and Philippine Scouts, troop of cavalry, machine-gun platoon, and Signal Corps field company. Price, $12.15.
The latest issue of this glass known as the Type A, model 1910, includes provision for interpupillary adjustment, the two barrels being hinged to accommodate the glass to the distance between the pupils of the eye. The price of the model 1910 glass is $14.75.
Type B:
This field glass is similar in appearance and construction to the Type A glass, and is issued to the field artillery organizations upon requisition. The following is a brief description:
Magnification, 4½ and 6½ diameters; Galilean type; object lens, 1¾ inches; interpupillary adjustment; tan leather finish; tan leather carrying case with compass; weight of glass, complete, with case, cord, and straps, 26 ounces; length of glass closed, 4½ inches. At a distance of 1,000 yards the field of view includes a diameter of 90 yards for the 4½ power, and 60 yards for the 6½ power. This glass is issued as a part of the fire-control equipment to field artillery. Price, $17.50.
Type C:
The type C is a high power glass of the porro prism type and is issued only to certain organizations of the field artillery, Signal Corps, and to all machine-gun platoons.
Description.—Magnification, 10 diameters; prismatic type; object lens, 1¾ inches; interpupillary adjustment; tan leather finish; sunshade; tan leather carrying case; weight of glass, complete, with case, cord, and straps, 46 ounces; length of glass closed, 7¾ inches. At a distance of 1,000 yards the field of view includes a diameter of 80 yards. This glass is issued to reconnaissance officers of field artillery. Price, $39.90.
Type D: Purchase has been made for delivery in the near future of a supply of a new type of high power prismatic field glass for sale and issue. This new type of glass, to be known as type D, is considerably smaller than the type C glass, as is shown by [figure 34]. The glass in a tan-colored carrying case weighs 15 ounces, the field glass without the case weighing but 9 ounces. The magnification is 8 powers and the field of view (with both eyes) 5° 40′. The estimated cost will be $27.