Fig. 418.—Reconnoitring glass, India pattern.
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863.—Reconnoitring Glass.—At present it is customary to use a binocular field-glass in preference to a telescope. The telescope gives greater penetration from its higher power; the field-glass is preferred for its wider field of view. The field-glass the author has supplied to the Indian Government has neutral-tint glasses centred on the eye-pieces to take off the glare when looking towards the sun, Fig. 418. These have also hinge joints between the pair of bodies, which permit adjustment of distance of centres to the distance of the eyes. The object-glass should be 1¾ inches, not over this. Where a telescope is used, the 30-inch—the original, not the present—India military telescope is to be recommended, Fig. 419. This is portable, has a sling case and a good 2-inch object glass. For lightness, aluminium bodies are preferred by many for both field-glasses and telescopes; at present the price of this metal is very low, so that it is probable it may become in a short time general for the purpose.
Fig. 419.—Army telescope.
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864.—Prism Binoculars.—These will be found a great improvement on the old form of field-glasses, as owing to the optical arrangement a high power is obtained combined with a larger field of view and good illumination. Fig. 420 shows the most modern form with all refinements; hinged body, central focussing and separate focussing to suit each eye. It has a very compact and strong body, and the size magnifying 8 diameters or about 64 times weighs only 13 ozs.
Fig. 420.—Stanley's prism binocular.