Making sense of all the binocular jargon

How to Choose the Perfect Pair of Binoculars

When you are reviewing or shopping for a good pair of binoculars, you’ll find that although many styles are similar, the price ranges are expansive. Why so? When it comes down to it, the price tends to reflect the quality of the optics. But what really matters when making your choice is what your intended usage is. That will determine the right set of binoculars for you. With this binoculars buying guide, I hope to educate you so you can make the right choice.

The Various Types & their Specs at a Glance…

Power of Magnification

The magnification and diameter of a pair of binoculars are identified by two numbers. The first is the magnification, and the latter is the front-of-lens diameter.

Let’s consider these now:

As by way of example, let’s take a set of binoculars with a magnification of 10 and a diameter of 32. The magnification, in this case 10x, offers information with respect to how close an object would appear in comparison to the unassisted eye. For this example, the object would be 10 times closer. Thus, if you were to view a deer that was standing 300 yards away through a 10x binoculars, it would appear as though it was 30 yards away.

In other words, 300 yards divided by 10.

Binoculars inside

Therefore, the higher the magnification the better you’d expect the view to be, right?

This is not necessarily the case because with respect to binoculars that possess a magnification of greater than 10x, they tend to amplify hand movement, which in turn makes steady viewing potentially rather tricky.

Objective Lens Diameter

The objective lens diameter is given in millimeters.

Taking the same example as above, 10 x 32, the objective lens measures 32mm.

The diameter of an objective lenses generally determines the amount of light the binoculars are capable of gathering. The higher the lens diameter, the more light will be gathered, which means that in low-light conditions, you’d be best served with a higher diameter.

Exit Pupil

The exit pupil provides an indication as to how bright objects will appear when they are being viewed in low-light conditions. The higher the number, the brighter the image will be.

How do you tell what the exit pupil is?

If you direct your binoculars at a source of light and hold them around a foot in front of your eyes then look into one or other of the eyepieces, you’ll notice a small, bright dot. That dot is the exit pupil. The exit pupil is an opening in the lens that permits the light to exit the binocular barrels and then reach the eye pupil.

Again, the exit pupil size is given in millimeters and can be calculated by taking the objective lens diameter and dividing that number by the magnification number.

As by way of example, a 10 x 32 binoculars will have an exit pupil of 3.2mm (32 divided by 10).

The wider the exit pupil diameter, as you’d expect, the more light that can pass through, which in turn makes a brighter, easier-to-see image when lighting is poor. Thus, if you anticipate that you’ll regularly use your binoculars in low-light – perhaps within dense tree cover, or at dawn or dusk, you’d be best served by investing in a model that has a higher exit pupil number – 4mm or higher.

Nevertheless, with respect to standard daylight viewing, the size of the exit pupil becomes that much less important. When lighting conditions are good, the human pupil narrows to around 2mm. The size of the exit pupilin all binoculars is this size or larger.

However, when the light is dim, our pupils can dilate up to 7mm. For instance, with a 7 x 50 binocular, the size of the exit pupil would be 7.1mm, and that would offer a good choice for use in low-light conditions.

Furthermore, a larger exit pupil will make it easier to maintain a full image irrespective of hand-shake or movement.

Relative Brightness

If you square the exit pupil number, you’ll be able to determine the relative brightness. With a higher relativebrightness, the brighter the image you will see. Again, this is a useful attribute when using binoculars in low-light conditions.

So, for example, a binocular that offers an exit pupil of say, 4.5, when you square this number (4.5 x 4.5)you’ll find that the binocular has a relative brightness of 20.25.

A question that may be on your mind right now is, will an exit pupil size on one pair of binoculars which is identical to that of another pair of binoculars produce identical levels of brightness? Actually, no.

Particularly with respect to the higher-end binocular models, manufacturers will assert that there are a varietyof refinements to take into account – lens elements, prism type, optical coatings, and quality of components – they all impact the relative brightness.

Eye Relief

The eye relief represents the distance between the eyepieces and your eyes at the time that the whole field of view is visible. With longer eye relief, there’s an increase in user comfort because you are able to hold the binoculars away from your face.

If you wear spectacles or regularly use sunglasses, a higher eye relief spec becomes particularly useful.

Binocular manufacturers will generally recommend that those who use glasses ought to roll the rubber eyepiece collars down prior to use. However, do note that there are some exceptions to this rule.

Should you use eye glasses, it’s advisable to invest in binoculars that provide an eye relief of at least 11mm.

Field of View

The field of view lets you know the width of the area, which is normally given in feet, that you are able to view at a glance at a distance of 1000 yards from where you are located. A wide field of view is good for viewing wildlife like birds or deer. In general, a higher magnification will result in a narrower field of view.

Making Your Decision

Once you’ve made a decision with regards to the category, the choice of a particular model depends on budget and then the variable factors such as those given above. It also depends on whether you will be using your binos to hunt deer, or to look at birds. But do keep in mind that any set of binoculars is only as good as the optics they utilize.