The function of binoculars is twofold. They allow to swell the observed objects and increase their apparent brightness. This brightness gain enhances colors and contrast of the observed objects, and sometimes can see the stars invisible to the naked eye. Moreover, contrary to telescopes, they offer a stereoscopic vision (with 2 eyes).

Optical Designs

Binoculars are composed of two symmetrical telescopes connected in parallel. The light passes through:
1. The main lenses that magnify and reverse the image.
2. Then the prisms that straighten the image to provide a right side up vision, and reduce the focal length.
3. And finally the eyepieces that enlarge the image.

There are 2 types of binoculars, each with different prisms :


With this type of prism, the light rays undergo orthogonal trajectory, and the eye are not aligned with the main lenses. The porro prism binoculars give the image a great relief effect. The developed system is outside.

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Binoculars with roof prisms are also called straight binoculars. The light rays follow a path in acute angle and the eye are aligned with the main lenses. In this type binoculars, the focusing system is located inside the tube. The latter type of development allows a more solid construction and protection against moisture.

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Binoculars Settings

Spacing Eye ] A central mechanical axis to adjust the distance between the eyes, in order to adapt the pupillary distance of the observer. It is essential that eye are positioned exactly opposite to each eye, otherwise the images of the two eyes appear edged with black, or will overlap. The pupillary distance (PD) is expressed in millimeters.

Focus ] The binoculars have a central focusing ring that allows you to adjust the sharpness of the image. High-end binoculars enjoy a depth of greater scope binoculars lower qualities, which reduces the need to re-focus.

Diopter Correction ] Moreover, most binoculars has an adjustment knob that allows you to compensate for any difference in visual acuity between the left eye and right eye. Depending on the model, the diopter adjustment is carried out on an eye (mostly on the right eye) or by a knob close to the focus knob. Some binoculars can block the diopter adjustment to avoid unintentional changes.

> How to adjust the binoculars?

1. Operate the hinge optical tubes to adjust the eye to him.
2. Close the eye that is in contact with the eyepiece with diopter adjustment dial and adjust the central wheel for a clear view.
3. Now close the other eye and adjust the diopter adjustment dial.

Eyecups (or studding) ] The twins have, at the eye, the eyecups for imposing a distance between the eye and the lens (eye relief) to minimize the entry of stray light and provide more stability, the twins being raised against the eyebrows. So they significantly improve visual comfort. The eyecups can be with or without wings; It all depends on the shape and width of the face of the observer.

For eyeglass wearers, there are many models on which are retractable eyecups.
We distinguish two types:

► Soft rubber eyecups which can be folded. Very convenient and comfortable, but as softening agents evaporate over time, they can become brittle.
► The eyecups hard plastic that can retract, turning. They have the advantage of being very durable and often have multiple breakpoints to block their position.


Here is our selection of the best binoculars for terrestrial observation and astronomy.