How Do Zoom Binoculars Work?

Binoculars are the world’s second most used optics besides eyeglasses. But these devices are sometimes the least understood piece of equipment. Today, I will look at one of the most common questions that I get often and which is How do zoom binoculars work?.

But before we look at these devices, let’s get to know what zoom binoculars really are. Here is my recent post, I compiled some of the top-rated zoom binoculars you will find in the market today.

What are Zoom Binoculars?

Zoom binoculars simply refer to binoculars that have variable magnification. These types of binoculars are designed such that you can alter their magnification range. Unlike their fixed magnification counterparts which have only one magnification, with the zoom binoculars, you can change the magnification from low to high or from high to low.

An example of such binoculars is 10-30×60 and 12-36×70. As you can see the objective lens diameter is fixed for both examples but their magnification is changeable. You can zoom out or zoom in with them. They are different from fixed binoculars which only have one magnification (e.g 10×).

how do zoom binoculars work

How do Zoom Binoculars Work?

These binoculars have adjustable oculars that allow you to move the magnifying power either from low to high or from high to low. The eyepiece lens which consists of several lens elements in housing makes the zooming function possible.

Zoom binoculars work by synchronizing the two telescopes that binoculars have using the zoom mechanism – which consists of moving lens elements with each eyepiece. This function is accomplished by the use of a flexible metal band ( as seen in the image above) that passes through the ocular arms, thereby connecting the zoom mechanism on the left to the zoom mechanism on the left side.

Unlike fixed binoculars that have pre-determined magnification and field of view, zoom binoculars have interchangeable eyepiece which allows you to reduce or increase the magnification while also altering the field of view. The zoom element makes this possible

Zoom Binoculars Advantages

Their major advantage is you can easily change the magnification from low to mid to high and vice versa with just a flick of your fingertips. This is useful when you are viewing long range targets in areas such as wetlands, on boats or from other activities such as sports events and concerts.

Zoom binoculars are great for stationary viewing. You can mount them on a tripod or any mounting device and be able to view stationary objects at any magnification without any problems. Unlike if you are moving, your body movements also get magnified when you increase the magnification.

Zoom binoculars are also good for applications like astronomy and surveillance. They are great at watching the planetary stars. This is because the stars and other heavenly bodies move slowly and their movement is not easily noticeable hence zoom binoculars work great when watching them.


After reading the advantages of zoom binoculars you might ask yourself why then buy fixed binoculars when you can get a single binocular with different magnifications?.

Well, because zoom binoculars use moving lens elements in each eyepiece, each image will shift slightly in same direction as the lens elements move.

The image shift typically moves the opposite way as the direction of the zoom lever changes. The result is binocular that is never in “perfect” alignment. As magnification increases, good alignment becomes increasingly important.

One of the reasons why people choose low magnification binoculars is because they offer a wider field of view. But because of the inherent design limitations of using moving elements within a zoom eyepiece lens, the field of view at the low-end range of the magnification becomes severely limited compared to fixed magnification binoculars.

If you compare a fixed-power binocular field of view with a zoom low magnification field of view, you will notice that the fixed magnification binocular has a wider field of view compared to the zoom.

For instance, let’s take the famous Nikon Action Zoom and Nikon Action Extreme binoculars fixed 10x binocular with a zoom 10-22x at the 10x magnification with the field of view compared at 1000 yards. The results are below.

  • Nikon 10-22×50 Action (Zoom): 199 ft
  • Nikon 10×50 Action Extreme (Fixed): 342 ft

You can see that the Nikon Action Extreme which has fixed power has a field of view almost twice that of the Action Zoom Binocular.

Zoom binoculars work great for some applications and might not be ideal for some. They work very well if the activity you want to use them for is not a fast-moving action. But if the action is fast moving, then you may have to weigh your options. They also work well with a pair of fixed power binoculars. Having the two is a good idea.

Beware of the marketing hype that some manufacturers project out there.  Manufacturers push the magnification levels to unrealistic levels in the effort to make their product appear most powerful or the best. Some as high as 100x which is ridiculously high such that the image quality is very degraded at these levels and getting an alignment is almost impossible.




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