Binocular FAQs

Binocular FAQs

Welcome to! We’ve tried to answer some of the most common questions we receive regarding our binoculars on this page.

What is the Outlet Diameter of a Binocular?

Outlet diameter, also known as the binocular objective lens diameter, is the diameter of the farthest lens from your eye.  A 8×40 binocular has an objective lens of 40 mm (the second number). The larger the lens, the more light the binocular can gather to produce brighter image.

What is Exit Distance of a Binocular?

In case you are holding your binocular a distance away from your eyes and towards the sky, you will see a little bright circle that forms in the middle of each eyepiece to its fullest form. This distance that you have taken the binocular in order to see this “circle” is the exit distance. It is popularly known as ‘eye relief’ and is the distance from the binocular eyepiece lens to your eyes where you will get the best image without eye strain. Those who wear eyeglasses will need a larger exit distance.

What is the Exit Pupil of a Binocular?

This refers to the diameter of the light beam that leaves the eyepiece if you hold your binocular with its objective lens pointed towards the source of light source (It is the diameter of the light circle that is formed when you determine your “exit distance” on your binocular) as we have seen above.

What is Field of view (FOV) of a Binocular?

This is the area of sky or even land that can be seen through your set of binoculars. It is often determined by the type of design of the binocular’s optics. FOV can be expressed as the width (feet) in 1000 yards or in degrees of the field of view.

What is BAK-4 Prism of a Binocular?

Prisms serve as mirrors. They reflect the incoming ray of light between the objectives and the eyepieces in order to invert the image projected by the objective lenses. When the image is inverted you get to see the exact object that you are viewing as it is. We have two types of prism that binoculars use namely the BK-7 and the BaK-4. The BaK-4 is preferred over BK-7 since they’ve got a higher refractive index with brighter and well-defined images.

What is FMC Lens?

Fully multi-coated (FMC) lenses are high-end optics with multiple coatings on their surfaces. FMC doesn’t guarantee top quality but are good indicators of a great binocular set. An FMC 8 x 35mm binocular may perform better than a normally coated set of binoculars that stands at 8 x 42mm.

Why do Binoculars use Green Coatings?

It is used to eliminate the red light effect from the image. This will reduce any apparent chromatic aberration. They also give images the blue-green cast. Nonetheless, some green coating will not give you the clear type image that you may need.

What is the Caliber of a Binocular?

This simply refers to the type or the level of binocular compared to the other sets of binoculars in the market. A higher caliber will have better features than a lower caliber binocular. We can even say that an FMC 8x42mm caliber is better than a normal 8x42mm caliber binocular.

What is a Range Finder of a Binocular?

The rangefinder of a binocular is the part of the binocular that will quickly help you to establish your current bearings and to also find distances. It comes coupled with a compass direction for easier an operation.

What is a Binocular’s Integrated Range Calculator?

A binoculars range calculator also works as a rangefinder. It helps you to determine the distances to objects that you are focusing on. However, it works better if you already know what the object’s height is.

What is a Binocular’s Diopter?

The diopter is the adjustable control knob that’s found on your binocular just right around the frame. The diopter is designed to allow you to compensate for the differences in sight levels between your two eyes so that you can see the image as it is.

In order to use the diopter, you will look at the object through your left eyepiece using your left eye then rotate the binocular’s focusing ring until a sharp image can be seen through it. Do the same with the right lens and the right eye. Then use the binocular once to view through.

What is the Center Focus Knob in a Binocular?

The center focus knob in a binocular is what you use to easily focus both barrels of your binocular at the very same time.

What is an IPD of a Binocular?

Also known as the Pupillary distance (PD) the Inter-pupillary distance (IPD) is basically the distance (measured in millimeters) between your centers of the eye pupils. It is also called the distance between your exit pupils or even the distance between the optical axes of a binocular system.

What is a Spotting Scope?

Spotting Scope is a type of compact telescope that is basically designed mostly for terrestrial observing. It is good for applications that will involve greater magnifications which are beyond the range of any typical binocular. Some binoculars spot this type of telescope.

What is a Binocular’s Aperture?

The word “aperture” comes from Latin word “aperire” which means “to open.” It is one of the most vital specifications of any binoculars that are used for astronomical observations. The aperture usually represents the diameter the objective lenses. A binocular that stands at 7×50 have 50 mm objective lenses in diameter which is also the aperture.

What is the Eye Relief in a Binocular?

This is basically the distance behind your eyepiece lenses when the image is in focus. The eye relief will indicate how far your binoculars can be held away from your eyes without distorting your field of view. A longer focal length of the eyepiece means a greater the eye relief.

What Do You Mean by Magnification in Binoculars?

Every binocular is described using a pair of numbers. A good example is 8×30. The first number, 8 including the x will always represent the magnification or “power” of the lens. It shows the degree to which the object you are observing can be enlarged.

Using the 10×42 as another example, the 10x will means the binocular set has 10x magnification power. This makes the object viewed through them to appear 10 times closer to you than they actually are or that they will appear through the naked eye.

What Does Baffling Mean in Binoculars?

Baffling shields against any stray light and even internal reflections. It can dramatically improve the image contrast.