Also known as binoculars. It is an observation instrument composed of two telescopes with the same performance that meets the requirements of people's eyes. It is a basic military observation instrument, used to observe the terrain, detect the enemy situation, and roughly measure the direction angle, high and low angle, and impact point deviation of the target. Non-military applications are also more extensive. The two lens barrels are generally connected by a hinged shaft as a reference, and the lens barrel rotates around the hinge axis to change the distance between the two eyepieces to adapt to the interpupillary interval of the observer's two eyes. The eyepieces can be adjusted "luminosity (visibility) and are equipped with a filter attachment.