What are Binoculars?

If you have found yourself asking What are binoculars just like the majority of us. Then you definitely need some good explanation. Here I will give a concise explanation of what these devices are. The detailed explanation of what binoculars are made of and the science of binoculars can be found here.

Binoculars also known as field glasses are two telescopes which are usually mounted on a single frame aligned side-by-side. They provide magnification for distant objects. They are handheld devices with each telescope dedicated to one eye.

what are binoculars?

The way binoculars are designed is you can easily adjust the focus of the telescopes by using one hand thumbwheel which is called central focus adjustment.

Once the central focus is adjusted, one of the two eyepieces can be further adjusted to compensate for differences between the viewer’s eyes. This is usually accomplished by rotating the eyepiece of each mount.

You can also still adjust one telescope focus separately if you need to adjust the view of one eye characteristics individually also referred to as independent focus adjustment. You would often find these in heavy field use binoculars such as military usage.

Unlike a monocular (telescope), binoculars are able to provide you with a three-dimensional image. Binoculars are designed such that you can even use them without glasses. For those who might be having vision problems, Most manufacturers have catered for those vision impaired in their designs by adding extra focus ability or larger eye relief.

There are also “focus-free” or “fixed-focus” binoculars that have no focusing mechanism other than the eyepiece adjustments that are meant to be set for the user’s eyes and left fixed.

These are considered to be compromise designs and works well from 40ft to infinity; within this range, they are able to work better, but not well suited for work that falls outside their designed range. They are ideal for uses in harsh environments and so make popular military, marine and skiing usage.

Magnification and Objective Lens

Binoculars are designed for different applications. Depending on the application it is used for, will require certain optical parameters. These parameters which you may often find on the prism cover plate of the binoculars. One of which is a magnification

Magnification which often is the first description you find on the binoculars description. Examples of such are;  7×35, 8×50.

The magnification is the first number (e.g., 7×, meaning “7 times”) and the second is the diameter of the objective lens in millimeters (1 inch is about 25 millimeters). It determines the resolution (sharpness). This figure is a measure of the light-gathering power of the instrument.

The bigger the objective lens number, the higher its ability to produce a brighter image under dim light but on the downside, it will result in a massive or bigger binocular. You will typically find those handheld binoculars that are used for hunting, bird watching, sports watching, nature study, or amateur astronomy range from about 6×30 to 10×50.


Magnification that is higher than these, are usually found in heavier equipment which cannot be held in the hand for a long time, therefore, such types of devices are mounted on a tripod to ease the weight on the user. Astronomical binoculars have diameters ranging from 70 mm to 150 mm.

The lens that is used on binoculars is generally coated to avoid reflections on their air-to-glass surfaces. There are also field glasses which have lower magnifications that are called opera glasses. They are less costly and have narrow fields of view and are usually made with magnifications of 2.5× to 5×.

Field of View

This figure is usually been noted in linear or angular form. The linear value is shown how many feet (meters) in width will be seen at 1,000 yards (or 1,000 m) and if it is noted in angular value, is how many degrees can be viewed. In general is inversely proportional to the magnifying power.

Eye Relief

It is the distance between the eyepiece lens and the viewer’s eye. It the distance that the viewer or user must position their eyes in order to get a clear image from far. Binoculars are designed with people who wear spectacles in mind. Binoculars may have eye relief ranging from a few millimeters to 2.5 centimeters or more. The longer the eye relief the better comfort you will feel while viewing.


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