Binocular Parts and Their Functions

Binoculars can have a variety of uses, from looking at distant objects when sightseeing, to birdwatching, to hunting. So, whether you are in your garden trying to identify that small brown bird fluttering in the undergrowth, or on a safari expedition to Africa, or even just sitting on the coast watching the ships sail by, life would be a lot duller if we didn’t have a quality pair of binoculars.

We all need them, but what are the Binocular Parts and Their Functions?

Well, let’s find out, starting with…

binocular parts and their functions

What Are The Different Parts of Binoculars?

Objective Lens

This is used to capture light illuminating a distant object.

Prism (Porro & Roof Prism Type)

This corrects the inverted image through the lenses to recreate the original perspective of the object.

Eyepiece/Ocular Lens

This presents the final image to the eyes.

Casing/Binoculars Barrel

This is used to keep the different parts of the binocular together in perfect alignment.

Diopter Adjustment

This allows customized viewing for different types and strengths of eyesight.

Focus Wheel

This allows you to adjust the focus of the Binoculars for objects at different distances.

Let’s now move on to look at the different components in a bit more detail…

Objective Lenses

This is the lens that is nearest to the object you are viewing, and therefore the furthest lens from your eyes. They are the lenses that catch the light from the object you are looking at.

The larger the lens diameter will result in a larger aperture, and therefore, they will capture more light. However, a larger diameter will also add to the weight of the binoculars. Therefore, you need to weigh up the improved clarity compared to the added weight if you intend on carrying them over longer distances.

binocular parts and their function

How can I tell how big the objective lens is?

They are shown in the binoculars specification by the number after the ‘x.’ Therefore, a 10×42 pair of binoculars would have a 42mm lens, while a 10×50 would have a 50mm lens.

They are made of glass which is then treated with an anti-reflective coating to capture the maximum amount of light to ensure a crystal clear view of the object as well as the best possible contrast.

In order to keep your lenses in tip-top condition, I recommend the excellent Zeiss Lens Cleaning Kit. It contains everything you need and is so easy to use. If you are looking for the best budget lens cleaning kit, I’d go for the Altura Photo Professional Cleaning Kit for DSLR Cameras and Sensitive Electronics Bundle.

Prism Pairs (Roof Prisms/Porro Prisms)

Whenever you look through a pair of binoculars, the object you are viewing appears in the same plane as you see with your naked eyes. However, in order to capture it, ready for magnification, the lenses actually flip the object upside down before returning it to its correct plane.

This function is taken care of by the Prisms, which are a pair of large structural wedges of glass. The first prism flips the object by 90 degrees before it is again flipped by the second prism by another 90 degrees. This makes a total of 180 degrees and therefore corrects the upside-down image that is created by the lenses.

Why are binoculars so heavy?

The prisms are the reason why binoculars are heavy in the middle, with the big lums of glass really adding to the weight.

Prism comes in two arrangements, either Roof Prisma or Porro Prism. Porro prisms are set up at 90 degrees to each other, while roof prisms feature a back to back arrangement.

If the objective lens and the ocular lens (eyepiece) are in line, the binoculars feature a roof prism design. Alternatively, if they are offset from each other, as with more traditional-looking binoculars, it is a porro prism design. The flatter, more modern roof prism designs tend to be more compact and lighter but will also cost you more to buy.

Eyepiece/Ocular Lens

This, as is quite obvious from the name, is the lens that is nearest to the eyes.

In basic terms, the objective lens creates the image, and then the eyepiece magnifies it and presents the enlarged image to your eyes. It is placed near the focal point of the objective lens and usually has a fixed field of view and magnification.

The magnification created by the eyepiece will depend on its focal length.

The eyepiece is a collection of lenses that are enclosed in a housing. In order to get an object perfectly in focus, the eyepiece is moved away from or closer to the objective lens using a thumbwheel.

the binocular parts and their function

Thumbwheel/Focus Wheel

This allows you to focus on objects that are at different distances from you.

It’s obviously important to be able to get a sharp and clear view of an object regardless of how close or far it is from you. This is achieved by rotating the thumbwheel and therefore adjusting the focus of the binoculars.

This will change the distance between the eyepiece and objective lens, allowing the focal point of the eyepiece to match the focal point of the objective lens, which will then bring the image into perfect focus.

The Barrel

This has a very simple but critical function in that it ensures that the eyepiece lenses, objective lenses, and prisms stay in perfect alignment.

Both barrels also need to be optically parallel to make sure that the image merges into one perfect circle. And also that the two barrels remain perfectly aligned with each other, regardless of the size of the gap between the pupils of your eyes.

The housing of most binoculars is covered with Gutta Percha, which increases its durability and longevity.

However, if you want the ultimate in protection, get yourself a pair that have a protective rubber coating. A great option is the Steiner 8×42 Safari Compact Nature/Travel Binoculars, or if you want something a lot more affordable, the CenterPoint Optics 73054 Compact Sporting 8 x 42mm Roof Prism Binoculars are excellent value for money.

Diopter Adjustment Knob

Everyone’s eyesight is slightly different, and when looking through binoculars, the optical system can affect both eyes differently, causing a strain on the eyes.

This will often result in a blurry image and might make you think that your binoculars are not working correctly. This is where the Diopter adjustment comes into play and compensates for any differences resulting in improved viewing comfort and crystal clear accuracy.

the binocular part and their function

Just look for the +/- …

It is usually located near or actually on one of the eyepieces and is marked with +/-. Simply turn it slowly until you achieve the best sight picture. Once set, it should no longer need any adjustment.

However, diopter adjustment will vary from person and person. Therefore if you share your binoculars with someone else, they may need to be adjusted more often if you both want the ultimate in clarity.

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Final Thoughts

You should now be aware of every part of your binoculars and what their role is. This should allow you to enjoy using your binoculars even more, and if you ever have a problem with them, you will have a better idea of what the problem could be and how to solve it.

So, until next time, enjoy your binoculars.

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About William Taylor

William is a U.S. Marine Corps veteran who served two tours in Afghanistan and one in Iraq. His duties included Security Advisor/Shift Sergeant, 0341/ Mortar Man- 0369 Infantry Unit Leader, Platoon Sergeant/ Personal Security Detachment, as well as being a Senior Mortar Advisor/Instructor.

He now spends most of his time at home in Michigan with his wife Nicola and their two bull terriers, Iggy and Joey. He fills up his time by writing as well as doing a lot of volunteering work for local charities.

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