The market offers a wide catalog of binoculars where we can compare and choose the best binocular for a wide range of applications including bird watching, nautical, camping, hunting, sports, concerts, surveillance, astronomy, etc. Whatever the needs of the user, there is a binocular whose design and features are suitable for this purpose.

To choose the most suitable binoculars, we must take into account various variables such as the environment, particular preferences, activity, etc.

Very important: if the observation distance is greater than 1 km, it is more than possible that what you need is to buy a terrestrial telescope. If so, we recommend reading our guide on Terrestrial Telescopes, selection criteria.


The brightness and definition of an image observed through the binocular in particular, are determined by various factors. Magnification, lens treatment, and objective lens diameter are just a few of the factors that affect the performance of binoculars.

However, the fundamental criterion concerning the binocular is the quality of its optics. Celestron is a brand that offers Quality-Price ratio offers high quality optics thanks to a careful selection of the glass and the optical treatment used, a precise manufacturing process, and exhaustive quality control.



Magnification is the degree of magnification of the observed object. For example, on 7×42 binoculars, the number 7 represents the “instrument magnification”. A 7x binocular magnifies the size of the object seven times relative to the naked eye. The degree of magnification affects the brightness of the image, so that the lower the magnification of a binocular, the brighter the observed image. As a general rule, an increase in magnification results in a reduction in the field of view.


The objective lenses of binoculars are located in the front of the same, and are those with the largest diameter.

The diameter, expressed in millimeters, of one of these lenses is the second characteristic number of binoculars. In this case, 7×42 binoculars have 42mm diameter objective lenses. The diameter of the objective lens determines the light-gathering ability of the binoculars, so the larger the diameter, the brighter and more detailed the image. This is especially useful at night and in low light conditions.

This may lead you to assume that the larger the diameter the better the instrument, but in reality, lens diameter must be considered along with other parameters such as exit pupil and binocular use to determine the most suitable one.


The“exit pupil”can be defined as the diameter, in millimeters, of the light beam exiting the eyepieces of a binocular.

The larger the exit pupil, the brighter the image obtained. Having a large exit pupil is advantageous for observations in low light and at night. In astronomical applications, the exit pupil of binoculars should be equated to the degree to which the observer’s pupil dilates after it has adapted to darkness.

To calculate the exit pupil, divide the diameter of the objective lens by the magnification. For example, the exit pupil of a 7×42 binocular is 6mm.


The field of area visible through binoculars is called the field of view. The angular field of view is usually indicated on the outside of binoculars, in degrees.

for linear field of view refers to the area visible at 1,000 yards (915 meters), and is expressed in feet. A larger field of view translates into a larger area seen through the binoculars.

The field of view is related to the magnification, at higher magnifications, the smaller the field of view. Also, a larger field of view causes a reduction in eye/eye distance. A wide field of view is convenient in situations where the object is moving. To calculate the linear field of view, multiply the angular field of view by 52.5.

For example, a binocular with a field of view of 8o covers a linear field of view of 420 feet (126 meters).


This concept refers to the distance, in millimeters, at which binoculars can be separated from the eye while maintaining a comfortable field of vision. Spectacle wearers will benefit from long distances.


It is the distance between the binoculars and the nearest object that can be focused, while maintaining a good image.


The ability of a binocular to capture and transmit enough light to obtain a bright and sharp image determines its luminosity.

The brightness of binoculars also enhances the differentiation of colors in the observed image.

The Relative Luminosity Index (R.B.I.), the Twilight Factor and the Relative Light Efficiency (R.L.E.) are common indices used in the binoculars industry, however, in many cases they are concepts that are misunderstood or applied meaninglessly.

Brightness is a concept to take into account when choosing binoculars, but it is not the most important factor.

The luminosity depends on several parameters including the diameter of the objective lenses, the magnification, the type and quality of the glass used, the treatment of the optics and the type of prisms used. As a general rule, large diameter, low or moderate magnification, fully multi-coated lenses are best suited.


The prisms in binoculars are used to invert the image and are available in two designs: roof and porro. By design, roof prisms are lighter and more compact. The prisms are designated as BK7 (boron-silicate) and BaK-4 (barium crystal). Both are inexpensive and very effective. BaK-4 design glass has a higher density (refractive index) and virtually eliminates internal stray light, producing high-definition images.


Contrast refers to the degree of differentiation between two light and dark objects and the background of the image. High contrast helps to see faint objects and discern subtle details. Contrast is affected by resolution.
The better the resolution, the higher the contrast. High-quality optical treatments offer high contrast in images. Other factors that affect contrast are collimation, air turbulence, and the quality of objective lenses, prisms, and eyepieces.


It is the measure of a binoculars ability to distinguish fine details and produce sharp images. A good resolution offers a greater color intensity. Resolution is directly related to the diameter of the objective lenses. Generally, a larger diameter lens offers more detail than a smaller diameter lens, regardless of the magnification of the binoculars. Actual resolution is determined by the quality of the optical components, the type and quality of optical processing, atmospheric conditions, optical alignment (collimation), and the visual acuity of the observer.


Collimation is understood as the alignment of the optical elements of binoculars in relation to their mechanical axis.
Good collimation prevents eye strain, headaches and double image sensation while improving resolution.


As the distance between the eyes of the observers is variable, the eyepieces of a binocular have to be adjusted for each observer. Most binoculars have an adjustable bracket that allows the eyepiece tubes to be pushed together or separated. This process is called “inter-pupillary distance adjustment”(IPD).


The focusing mechanism enables precise focusing of objects at different distances to be achieved. Most binoculars have a central focus or a separate focus mechanism.

Center Focus

This mechanism uses a single knob to move the eyepiece tubes until a defined image is obtained. However, since each person’s vision is slightly different in each eye, center focus drive binoculars use a diopter corrector to compensate for this difference. The diopter corrector allows one of the eyepieces (usually the right) to be individually focused.

Independent Approach

It allows high-precision adjustments acting on each eyepiece independently.


The optical elements (10 to 18 surfaces) of binoculars are treated to reduce internal light loss and glare. Below are various optical treatments of the binoculars, from lowest to highest quality:

Uncoated – No optical surface is treated. Less than 50% of the light is transmitted through the binoculars, which causes a lack of contrast with parasitic brightness that makes observation unfeasible.
Coated – One or more surfaces are treated. The overall quality is poor.
Fully Coated – All air-separated surfaces are treated with an anti-reflective magnesium fluoride coating(MgF2). The transmission capacity approaches 80% and is acceptable for most users.
Multi-Coated – One or more surfaces are treated with multi-layers of a chemical compound and the rest with Magnesium Fluoride.
Fully Multi-Coated – All air-separated surfaces are treated with multiple layers of a chemical compound.
Binoculars that include this treatment offer a transmission of 90 to 95%. The result is an extremely bright image with maximum contrast.

There are many brands that offer binoculars with a good quality-price ratio, but if we have to recommend one, it is undoubtedly the Uscamel binoculars. This brand is of China origin and manufacture where it maintains a very good balance in resistant design and optical performance.

You may also like:
Binoculars Buying Tips for Choosing the Right Binoculars
The Best Binoculars for Bird Watching
Binoculars Basics & Purchase Advice
Uscamel Entry into Digital Astronomy
Should I Choose 8×42 or 10×42 Binoculars
How to Choose an Ideal Pair of Binoculars for Hiking?
The Right Binoculars for Bird Watching
Monocular or Binocular, Which is Better?