BINOCULARS IN IDENTIFICATION OF AIRCRAFT
Once an aircraft has been detected, ground observers should use binoculars to aid visual recognition. Time for identification is limited. Identification of a fast-moving jet aircraft must be completed within about 5 to 15 seconds. The observer will lose valuable time if he fumbles or tries to readjust his binoculars at this stage of the game. This appendix tells how to adjust and use binoculars in identifying aircraft.
Loss of efficiency occurs if the binoculars are not held correctly to the eyes. Binoculars are held as shown in illustration below.
They should be held tightly, with the monocles resting on and supported by the heels of the hands. The thumbs block out light that would enter between the eyes and eyecups. The eyecups are held lightly to the eyes to avoid transmission of body movement. When observing with the binoculars, use a stationary rest for the elbows, if possible.
Binoculars must be prefocused and adjusted prior to use.
The distance between the eyes of individuals varies. The two monocles that make up a pair of field glasses are hinged together so that the lenses can be centered over the pupils of the eyes. The hinge is equipped with a scale which indicates in millimeters the interpupillary distance. To find the correct setting, look through the binoculars and adjust the hinge until the field of vision appears as a single, sharply defined circle. Once the interpupillary adjustment is correctly made, remember the scale setting so that no time is lost when the glasses are used again. Record the setting for future use.
Each eye of an individual requires a different focal setting. Adjust the focus for each eye as follows:
Polarized filters eliminate glare and should be used if available.
Binoculars are a positive aid in aircraft recognition. By magnifying the aircraft's image, they aid the observer in distinguishing recognition features at long distances. In contrast, use of binoculars for search and detection tends to reduce detection range because of their limited field of view. Some tips on using binoculars are as follows:
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