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At the front of each telescope is a lens—either an objective or a field lens. This gathers light from whatever it is you’re looking at. Let’s says you're looking at a bird. The objective or field lens magnifies the image of the bird, but this image is upside-down. Not very useful at this point.
If you’re using prism binoculars (and most likely you are—they’re the most popular kind), a prism in each tube reverses and inverts the image of the bird. In field glasses, there’s a second lens instead of a prism.
The light then travels down the tube, and through a lens in the eyepieces. The bird is magnified even further. Good binoculars will give you an accurate and detailed look at the bird.












binoculars are, two identical telescopes placed next to each other.
At the front of each telescope is a lens, called the objective. Its role is to gather light from whatever it is you're looking at and bring it to a focus in the eyepiece, where the light is formed into a visible image and magnified to take up a large portion of the retina. The magnification depends on the focal length of the eyepiece, and for binoculars it is usually between 5x and 10x.
Prisms used in binoculars are blocks of glass that function as mirrors, but without a mirror's reflective backing. They come in two models and use different types of glass. Their role is to bring the light beams from the objective closer together by means of internal reflection, and also turn the image right-side up and orient the view properly left to right.
the image above shows the path of the light as it enters the objectives, passes through a set of prisms that turn the image right side up, and finally leaves the eyepieces to enter the observer's eyes.
This applies to all binoculars, no matter what z da model or size.