Numbers on Binoculars [How to Use Them] – Nov, 2022

Many products seem to have something that has some hidden meaning printed on it. In fact it seems that apart from safety warnings, manufacturers are never keen to explain numbers printed on their products. The numbers on the binoculars are no exception. Here is what the numbers on the binoculars mean and how you can use them to choose the best binoculars. The two number printed on the binoculars tell you about magnification and transmission of light. Read on to find out more.

What Do the Numbers Mean on Binoculars

Magnification Diameter

All binoculars are generally referred by two numbers with an “x” separating them, e.g. 8×42. The first number always represents the magnification of the binocular, which in this case the object will appear 8 times closer than when viewed using our naked eye. When using binoculars that got a magnification of more than 10x, it is recommended to always use a tripod as bare hands will make the object appear shaky.

Objective Diameter

The second number always represent the objective diameter, this allows the transmission of light that is going into the binocular. The size here matters as large objective lens will allow more light through compared to the small ones.

Exit Pupil

An exit pupil is a number that is always seen at the specification table of binoculars. This refers to the amount of light that is visible in the eyepiece, the amount of light always depend on the size of exit pupil as large exit pupils make images brighter. The size is determined by dividing the objective diameter with the magnification.

An exit pupil of 2.5 or 3mm is ideal for normal daylight viewing while 5-7mm is preferred for astronomy. More than 7mm of the exit pupil is waste of light as the human eye cannot open to that extent. Light transmission in a binocular is the ability of the optics to deliver maximum light entering the objective lens to the eye.

Relative Brightness

The relative brightness is simply the square of an exit pupil. Therefore, an exit pupil of 4mm in a binocular will have an RE of 16.relative brightness treats all binocular regardless of their optical quality and lens coating as if they are equal. A test conducted revealed that some premium grade compact having low relative brightness were indeed brighter than binocular that are full size.

Twilight Factor

The twilight Factor is a mathematical formula that estimates the amount of detail visible in low light condition. It’s derived by multiplying the magnification and the objective diameter then finding the square root of the answer. e.g. 10×40=400 (square root of 400 is 20 which is the twilight factor).as with relative brightness and exit pupil, the twilight factor cannot be taken literally as it treats all binocular regardless of their optical quality and lens coating as if they are equal.

Eye Relief

The eye relief is the distance between the eye and the binocular. Extended eye relief is ideal for sunglasses wearer as they reduce eye strain. Diopter adjustment can be used by those who don’t wear eyeglasses and don’t have 20/20 vision.

Field of View (FOV)

The FOV is the side-to-side measurement of the field area. This is always determined by two things, first, it is magnification which, as it goes up, the field of view narrows. The second thing is the design of the eyepiece, the wide angle is known for their good quality of optics on the eyepiece though they are expensive.

Binocular Types

There are only two prism systems that binoculars come with, that is roof prism and Porro prism. The roof prism binoculars we find that the prism overlap making it able for the objective lens to line directly with the eyepiece. In the Porro prism, the objective lens is always offset from the eyepiece. The Porro prism design offers a wider field of view and greater depth perception. Majority of the optical systems are made from borosilicate (BK-7) barium crown or glass (BAK-4) glass. This is the best quality glass for high edge sharpness and brighter images:

  • Standard size binocular, which can be used for anything from sport to nature observation
  • Compact binoculars which are light in weight and smaller ideal for theatres, concert, hunting or even hiking
  • Wide-angle binoculars are the best for tracking fast moving actions. They are ideal in wilderness terrain, football field, and racetracks
  • Zoom binoculars allows the user to increase the magnification of an image to view the object in detail.
  • Waterproof binoculars are ones, which deliver clarity even in bad weather condition such as fog, rain, and ice. They are O-ring sealed and purged with nitrogen.
  • Armored binoculars are the kinds that have a rubber or a synthetic material fabric to protect the casing from mechanical damage. This makes the user comfortable while holding them and protects them from scratches and breakage resulting from falls.
  • Center focus binoculars are the ones that use single wheel to focus on an image.it is versatile as it can focus on both far away and close objects.
  • Individual eyepiece focus binoculars are the kind that allows the user to focus on each eyepiece when looking at an object. Objects that appear from 40 yards are always on focus and doesn’t require focusing. It’s ideal for medium and long range objects.
  • No focus or focus free binoculars are the kinds where the eyepiece are set and cannot be adjusted. This implies that you can’t focus on an object appearing below 40 yards and can’t adjust the strength in each eyepiece.

Optical Coating and Light Transmission

Objective Lens of Binocular

The optical coating is the most important element in a binocular. This is because, as light hits the lenses, some of it is lost and cannot be transmitted, coating, therefore, will help to achieve a higher light transmission. Binocular is always identified as coated, fully coated, multicoated and fully multicoated lenses. The type of coating will, therefore, determine the level of light transmission in a binocular.

Binocular Tips

Binocular weights- binoculars that weighs 30 ounces and below are comfortable to carry around on the neck. If your binocular is more than 35 ounces, it’s good to look for other places like shoulder to carry them.

Tripod mounting-binoculars with the magnification of over 10x should be attached to the tripod to avoid shaky images. Also, binoculars last number being 70mm or more needs a tripod.

Cleaning the lenses-its recommended using microfiber cloth when cleaning lens surface in a circular motion so as to protect the coating. Avoid using finger and sharp objects