TLDR: Binoculars are like two small telescopes that you hold up to your eyes. They help you see faraway things up close and in 3D.
Binoculars are a pair of telescopes that are mounted side by side. They are designed to be held with both hands, although they come in different sizes. When you look through binoculars, you use both of your eyes, which gives you a three-dimensional image. This is called binocular vision. Binoculars are used to view distant objects, like birds, animals, or even stars.
There are different types of binoculars, each with its own optical design. One type is called Galilean binoculars, which have a convex objective lens and a concave eyepiece lens. These binoculars provide an erect image, but they have a narrow field of view and can't magnify very much. Another type is Keplerian binoculars, which use a positive eyepiece lens to view the image formed by the objective lens. These binoculars can provide higher magnification and a better image quality.
Binoculars also have different optical parameters that determine their performance. The magnification of binoculars tells you how much closer the object will appear. The objective diameter refers to the size of the front lenses, which affects the amount of light that enters the binoculars. The field of view is the width of the area that you can see through the binoculars. The exit pupil is the size of the beam of light that enters your eye, and it should match the size of your pupil for the best image quality. The twilight factor and relative brightness are measures of how well the binoculars perform in low light conditions.
Binoculars also have mechanical features that affect their usability. The focus and adjustment of binoculars allow you to bring the image into sharp focus. There are different types of focusing mechanisms, such as independent focusing and central focusing. Binoculars can also be adjusted for the interpupillary distance, which is the distance between your eyes. Some binoculars have image stabilization technology to reduce shake and improve image stability. The housing of binoculars can be made of different materials, such as metal or plastic, and can be rubber armored for a better grip.
In summary, binoculars are a pair of telescopes that help you see faraway objects up close and in 3D. They come in different types and have various optical and mechanical features that affect their performance and usability.