Fujifilm Optical Division Blog
If you haven’t watched the first two parts of our “Binoculars 101” series, you may want to take a few minutes to catch up on the basics, including the two main types of binoculars. With that foundation of binocular configurations, styles and applications, you’ll be ready for this tutorial on how binocular lenses operate. You can watch the full video by clicking below.

We’ll begin with the Exit Pupils. To locate them, simply hold a pair of binoculars at arm’s length and look for the disks of light that appear to lie on the surfaces of the eyepieces.

The Exit Pupil is the virtual aperture in an optical system. It’s important because only the light which passes through it can enter your eyes. So, all other things being equal, the larger the exit
pupil, the more light will be delivered to your eyes, providing greater brightness.

To calculate the exit pupil of any binocular, take the effective diameter of the objective lens and divide by the magnification. For example, a 7x50 has an exit pupil of 7.1, as you divide 50 by 7. An 8x20 exit pupil is 2.5—the results of 20 divided by 8. If all the other specs are the same, the 7x50 will have a brighter image than the 8x20.

The ideal exit pupil diameter depends on your application. Large exit pupils are an advantage in low light conditions. Most compact binoculars with smaller exit pupils are sufficient for the daytime but quickly degrade as the amount of light decreases.

When it comes to the big picture, your landscape is called the Field of View, or FOV. This is the horizontal width of the image you can see at a given distance. In binocular specifications, it is usually expressed as the number of feet at 1,000 yards. It is also expressed in degrees—as in angles—known as Real Field of View.

The higher the magnification, the narrower the Real Field View will be. To convert the angle into linear form—or feet—simply multiply the angle by 52.5. So, if the angle for a 7x magnification is 7 degrees, then you take 7 times 52.5 to get a Real FOV of 367 feet.

Now that you have a handle on Exit Pupils and Field of View, we can move onto Interpupillary Distance, or IPD. Binocular barrels rotate around a hinge so the user can line up the eyepieces with their eye pupils. Normally expressed in millimeters, the IPD measures the distance between the centers of a binocular’s two eyepieces and the distance between the centers of a user’s eye pupils. When the IPD on a binocular is correctly set, you will see one circle in the viewing area—not two, as Hollywood often incorrectly depicts.

Full-size binoculars work well for the majority of people. Since compact double-hinge binoculars generally have a narrower IPD, they work well for anyone who has a very narrow IPD, such as a child.

Fujinon binoculars have a typical Interpupillary Distance of 53-74mm, depending on model.

If you are reading this through a pair of eyeglasses, it’s important to note that every binocular has what’s called Eye Relief. This is the distance between the eyepiece and your eye, where you can obtain a full Field of View, and it only affects people who wear glasses. If the Eye Relief is insufficient—or short—vignetting will occur around the edges for those who wear glasses. More specifically, binoculars with Eye Relief of 10-12mm typically won’t allow an eyeglass wearer to get the full field of view. On average, you’ll need at least 15mm of eye relief. 

Fujinon binoculars have Eye Reliefs that range from 15mm-23mm, depending on model and magnification. It’s a good idea to test out any pair of binoculars with your glasses on to determine if the eye relief is sufficient.

There’s one final, key aspect to binocular lenses, and that’s Apparent Field of View. This is the angle your eye would move through if you looked at one edge of the field and scanned over to the opposite edge. To get the value of the Apparent Field of View, simply multiply the magnification by the Real Field of View. For example, if the magnification is 7x and the real FOV is 7 degrees, multiply 7 by 7 and the Apparent FOV is 49 degrees. The rule of thumb is that an Apparent Field of View more than 62 degrees is considered to be a wide angle binocular.

If you’ve watched the other two videos in this series, you now have almost all the information you need to make an educated purchase. You know what the two types of binoculars are, how the lenses work, and their basic components and applications. There’s just one more area you need a primer on: coatings. Lucky for you, that’s our next and final video in this series! Tune in to our YouTube channel to view the whole series and visit our website to learn about Fujifilm USA’s full line of binoculars boasting high optical performance and reliability for a vast range of applications.

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Posted: 7/12/2016 1:57:42 PM by Thom Calabro | with 0 comments

You may or may not know that Fujifilm produces a full line of binoculars boasting high optical performance and reliability. From high-grade models for professional users to a whole range of binoculars for enthusiasts of various sports and activities, it takes a little research to keep the particulars in focus. That’s why we’ve created a four-part video series to help you navigate the waters. In the first installment, we start with “the numbers.” Watch the full video by clicking below, and you can watch the entire series on the Fujinon Binoculars YouTube channel.


The digits on binoculars describe the configuration. For example, with the 8x42 binocular, the first number—8— represents the magnification. In this case, an object will be eight times closer with the binocular compared to looking at the same object with your naked eye.

The second number—42— is the size of the Objective in millimeters. The Objectives are the larger lenses at the end of the binoculars. The larger the Objective, the better its ability to collect light.

So, which set is right for you? Start by identifying how you’ll be using them. While a 7x50 or a 10x50 may be ideal for an astronomer, a birder may want to opt for something smaller, like the aforementioned 8x42 or 10x42. There is no one “best” binocular—it all depends on your needs. Let’s take a deeper look into some common applications.

Astronomers want binoculars with magnification that also gather a lot of light. The best choices here are the 10x50, 7x50, or a FUJINON FMT 10X70 or 16X70.

Birders want binoculars with light-gathering ability and to see their objects as closely as possible. For this application, compact sized 42mm, with their large exit pupils, are good choices.

Hunters want low light performing binoculars, as they typically use them at dawn or dusk. The best options here are the 42mm or 50mm binoculars with optimal coating.

For marine use, 7x50 binoculars are generally your best choice. The lower magnification of a 7x binocular makes it easier to hold steady amidst the movement of the waves, while the larger 50mm objective lens is ideal for seeing detail in low light.

Stabilized binoculars are also ideal here, making FUJINON’s Techno-Stabi binoculars—with their high magnification and very effective stabilization—an excellent choice.

Waterproofing and fog proofing are major considerations when choosing binoculars. Those that are both waterproof and fog-proof are highly recommended for environments with high humidity, rain or water. A binocular that becomes compromised by moisture will ultimately become unusable due to the mold growing in the barrels.

Waterproof binoculars are sealed but the oxygen inside the binocular has not been purged. Fog-proof binoculars have been purged and the oxygen inside the barrel has been replaced with nitrogen or argon gas.

Fog-proof binoculars are always waterproof, but binoculars that are waterproof are not necessarily fog-proof.

All Fujinon binoculars are 100% water and fog-proof.  This means they’re sealed with O-rings to prevent moisture, dust and debris from entering the barrel and the eyepiece of the binocular. And, of course, the oxygen has been purged.

Those are the basics of the basics. There are a few other areas you’ll want to brush up on before deciding which binoculars are best for you. Tune in to the rest of the series, right here on our YouTube channel, and be sure to explore Fujinon.com or Fujifilmusa.com for more information on Fujifilm Optical Devices.

Have a question, or something to share? We’d love to hear from you! Connect with us on Facebook or Twitter

Posted: 2/23/2016 11:58:47 AM by Thom Calabro | with 0 comments


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