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binocular faq

People have lots of questions when it comes to binoculars. Looking over the different brand names and varieties, it can be quite confusing trying to understand what all the different features mean. With our Binocular FAQ, we will cover all the basics of what you need to know about binoculars. This will dispel all the confusion and help you choose the right pair with confidence.

To skip to a specific topic just click on a link below or continue to read the article in order

What Do the Numbers Like “8×40” Mean?

These numbers are the primary way that manufacturers classify their binoculars. They are also probably the most important numbers you should pay attention to when you are considering which binoculars are right for you.

The first number refers to the level of magnification offered by the binoculars. If the number is “8,” it means that when you look through the binoculars things will appear 8 times larger than when just looking at them with the naked eye. So, for example, if you see a deer 300 yards away and look at it through binoculars with 8x magnification, it will appear as if it were 37.5 yards away (300 ÷ 8).

The second number in “8×40” refers to the diameter of the objective lens, or how large the lens taking in the light is. This is measured in millimeters. The larger the lens, the more light is able to enter into the binoculars. While this might sound like you would want really large objective lenses, there is not really much advantage going beyond 50mm. These lenses are more than enough in most situations to let in plenty of light to see in even low-light situations.

What Do the Numbers Like “8-24×50” Mean? What About “8/24×50”?

When numbers like this appear in the description of the binoculars, it means that the zoom of the binoculars is variable. When it is separated by the dash “-” it means that the zoom can be adjusted manually with a dial between those ranges (i.e., between 8x and 24x).

When it is separated by a slash “/” it means that the zoom can be adjusted by switching the lenses out. This would mean you would need to carry more than one lens set to make the zoom change. Unless you are shopping for very high-end binoculars, these figures usually do not come in as a factor.

What Is “Field of View”?

This is another figure you will often find listed by manufacturers in the specifications for binoculars. The “field of view” refers to the width of the area you can see when you look through the binoculars. This is usually measured at 1,000 yards. So, if the field of view is 280 feet, you can see that far across at 1,000 yards when looking through the binoculars.

Generally speaking, the larger the magnification, the narrower the field of will be. The field of view will also depend on how far the objects actually are away from you. If you will be tracking things that move, a higher field of view is a good idea since you can capture more in a single glance.

What Does “Exit Pupil Diameter” Mean?

The exit pupil diameter is the opposite of the objective lens measurement. That is to say, the exit pupil diameter refers to the lens you look through directly. More properly speaking, it refers to the shaft of light that finally comes through the lenses after coming through the binoculars and finally enter the eyes.

Manufacturers do not usually list the exit pupil diameter in their specifications because you can calculate it yourself by dividing the objective lens size by the magnification. So, for binoculars which are 8×40, they would have an exit pupil diameter of 5mm. The more light that is coming through the binoculars, the brighter the images will appear.

What Is “Eye Relief”?

Eye relief refers to the optimal distance that the eyes should be from the binoculars for viewing. The shorter the eye relief, the closer the binoculars have to be to your eyes in order to see through the binoculars well.

This is a factor you should pay attention to if you wear eyeglasses. You need to look for an eye relief of at least greater than 11mm. If the eye relief is less than 11mm, then you will not be able to see through the binoculars while wearing your eyeglasses.

What Is “Multi-Coating”?

This is something that you will find listed on most binoculars today. When light passes through a lens, as much as 5% of the light will be reflected and scattered (i.e., lost). To correct for this, manufacturers add a layer of preventative coating. This coating reduces the amount of light loss due to the natural conditions of the glass.

The number of layers of coating determines the degree to which the scattering effect is minimized. Binoculars which are listed as “fully multi-coated” means that the maximum amount of coatings have been added which reduce the scattering of light down to .25%.

What Does “Roof Prism” Mean? What About “Porro Prism”?

Both “roof prism” and “Porro prism” refer to the way in which light is reflected inside the binoculars. Light does not simply travel from one lens to another to magnify an image. This can easily be seen by the fact that on most binocular lenses do not line up perfectly.

“Porro Prism” refers to an older method of reflecting light in binoculars that were the standard well up until the 1960s. Most binoculars today use roof prism reflection which is far superior in transmitting sharp and clear images.

How Are Binoculars Made Fog Proof?

Most quality binoculars today are made both waterproof and fogproof. The waterproofing is easily accomplished by using seals that resist water penetration.

To fog proof binoculars, manufacturers purge the internal chambers of the binoculars of all air and replace it with an inert gas like nitrogen. As humidity levels rise and fall, this means no moisture will gather on the binoculars. This is particularly useful is you plan to use your binoculars in the early morning when the glass has a tendency to fog.


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