The Ideal Birdwatching Binocular

With thousands of options available it can be very difficult for someone interested in finding the perfect pair of binoculars for birdwatching. This guide will be present you with the basic knowledge and recommendations you need to find the optimal pair.

Magnification: The ability to bring an image closer to the eye is what binoculars are fundamentally designed to do and what magnification achieves. Each pair of binoculars is identified by a magnification power number, for example, a magnification power number of 8x means that the object you are focusing on will be appear 8x times closer than it would appear to the naked eye. When it comes to birdwatching the most common magnification powers are between 6x and 12x. Generally the lower the magnification, the less the binocular weighs, which is a big deal when it comes to watching birds, because hand shake (which occurs when the hands/arms become fatigued from holding the binocular for an extended period of time) can greatly disrupt the view the binocular provides, for this reason a 12x magnification should really only be used for birdwatchers who feel they need extra magnification. On the other side of the equation, too low a magnification can make it difficult to view birds that are not conveniently close, for example a 6x power is not going to show great detail of a bird high up in a tree or a hawk soaring in the sky. For these reasons a magnification power within the ranges of 7x-10x are widely considered the best options for viewing birds. At a 7x-10x magnification power hand shake shouldn’t be much of an issue, while the magnification should be strong enough to show impressive detail in birds nearby and from afar.

Ideal Magnification: 7x to 10x

Objective Lens Diameter: Light is a very important subject when it comes to understanding binoculars because it dictates image brightness. No component of the binocular itself relates more to light than the objective lens diameter. The objective lenses are the two lenses at the top of the binocular, the lenses closest to the object you are viewing. The objective lens diameter is simply a measurement of the diameter of the objective lens (measured in millimeters). The larger the diameter the more light the binocular lets in, the brighter the image will be. Image brightness can be crucial in birdwatching with binoculars because the best times to view birds (as discussed in: Birdwatching Tips) are often early in the morning (before the sun is beaming) and towards the early evening (when the sun is getting ready to set). Usually magnification and objective lens diameter go hand in hand, what this means is that a high magnification is generally paired with a large objective lens (+50mm) which results in a heavier binocular and as a result the aforementioned hand shake. For this reason, it better to choose a magnification between 30mm and 42mm, a choice within this range will provide more than enough brightness to view birds early and late in the day. If you are very concerned about hand shake and desire a small binocular than staying in the 30s is the way to go, if you think can handle the slight increase in size, then something in the low 40s will provide a bit more brightness.

Ideal Objective Lens Diameter: Anything between 30mm to 42mm.

Field of View: When it comes to bird watching with binoculars the more you can see, the better. Field of View is a measure of the width of the area (usually measured in feet) you will be able to view from 1,000 yards away. Because birds are always on the move, they will be much easier to track if your binocular choice has a wide field of view. Generally, the higher the magnification power, the narrower the field of view. Which is another reason (in addition to hand shake) to go with a magnification of 10x or below. An acceptable field of view  bench point for birding watching with binoculars is 350mm but in most cases the larger the better.

Ideal Field of View: +350mm

Eye Relief: If you wear glasses (which many bird enthusiasts do) eye relief, which is the distance between the eyepiece and the eye, is very important. If you have glasses it is necessary to hold the binocular’s eye piece away from your eyes, if you hold it too far however it will reduce the field of view. Quality binoculars provide eye relief with an adjustable twist cup (usually made of rubber) that enables the viewer to hold the binoculars at the perfect distance between the eyepiece and eye. Even if you don’t wear glasses this can be helpful and even more comfortable but you don’t have to use the eye relief if you don’t want to. If you have glasses it is widely recommended that you get binoculars with an eye relief of at least 15mm.

Ideal Eye Relief: 15mm (if you wear glasses)

Focus: Nearly all binoculars use a focus wheel or knob, to focus in on the desired object. All focus wheels however are not created equal when it comes to movement and placement. The ideal binocular should feature a focusing mechanism that enables the user to quickly and precisely focus and adapt focus while viewing the unpredictable movements of a bird. To do this the focus wheel must move smoothly, it can’t be too stiff or too twitchy. The focus must also be located in a natural place, so it can be adjusted without having to shift hand position. Focusing shouldn’t be a big production, in fact, it should become something you don’t even have think about. The best way to judge the focusing mechanism is to try it out on a physical pair before you buy.

Ideal Focusing Mechanism: Smooth movement, natural location

Style: There are two primary styles of binoculars; porro-prism and roof-prism. The porro-prism style is the classic style, but it’s design makes it bulky, which leads to complaints over portability and weight. Roof-prism binoculars on the other hand are more compact and many consider them easier to hold and use. Note that roof-prism binoculars tend to be more expensive.

Ideal Style: Roof-Prism

Type of Glass: There are two glass types used in binocular prisms, they are BaK7 and BaK4, the difference between the two is their respective relationship with light, specifically it’s refractive index rate (I will not get into defining the refractive index rate, all you need to know is that the higher the rate, the better quality the image will be). Bak7 has a lower refractive index rating than BaK4 glass, so the image quality isn’t as good. That said, BaK7 glass is much cheaper and in some cases the difference between BaK7 and Bak4 is not very significant. The reason being is that not all BaK4 glass is created equal, as two types have emerged. The first and authentic BaK4 is barium crown glass – which is the best of the best and has the highest refractive index rating, it also the most expensive. The second type is the Chinese version of BaK4, which is made of phosphate crown glass. The refractive index rating of Chinese-made BaK4 is lower than the barium crown BaK4 but higher than BaK7 glass. So, in summary, barium crown BaK4 is the best, followed by phosphate crown BaK4, and then BaK7. Please keep in mind however that the casual binocular user shouldn’t be too concerned over the type of glass as the difference in image quality can be difficult to discern unless you are experienced with optics. Once you do become a binocular aficionado you will want to create as perfect an image as you possibly can, this will mean eliminating aberrations (distortions in the image). The most common (or at least discussed) aberration when it comes to binoculars is chromatic aberration which is when the imperfections of optics create a colored fuzziness around the object you are viewing. ED glass (which stands for extra-low dispersion) is used by some of the premium binocular brands because it is said to combat chromatic aberration.

Ideal Type of Glass: Bak4 (barium crown or phosphate crown, depending on your budget, ED an additional luxury if you can afford it).

Len Coatings: To increase image sharpness and brightness most binocular manufacturers add special coatings to the lenses. A single layer of coating is defined as “fully coated,” while multiple layers of coating are defined as “fully multi-coated.” These coatings tend to be proprietary and vary from binocular manufacturer to manufacturer, the lack of an industry-standard definition for coating terms can make it difficult to assess the quality of coating. For example, the number of coats a fully multi-coated lens has can vary greatly, a manufacturer can apply 2 coats and technically say the lenses are fully multi-coated, however a different manufacturer may apply 35 coats, under both scenarios both binoculars would be referred to as fully multi-coated. The quality of the coat can vary as well, some of the most expensive binoculars on the market only feature a single layer of coating. On roof-prism binoculars many manufacturers add a special phase coating, which is intended to create a more accurate color representation and a more vivid contrast. 

Ideal Lens Coating: Fully-Multi-Coated w/Phase Coating

Proofing: Most birdwatching is done outside in the elements and every serious birder has been caught in the rain, or worse. For this reason, you should strongly consider purchasing water-proof binoculars, sealed with O-rings because they will be able to withstand water submersion and also prevent debris like dirt and dust from gaining entry into the internal components. The last thing you want to do is drop a +$200 pair of binoculars in a muddy puddle and render them useless. It also makes sense to ensure that the binoculars you buy are fog-proof because internal fogging can damage binoculars. Please don’t assume any binocular you buy will be able to withstand the elements, verify that the item description explicitly states that the binocular is water and fog proof.

Ideal Proofing: Weather-Proof (with O-Rings) and Fog-Proof

 

Summary

So in review, the ideal birdwatching binocular specifications are:

  • Magnification: 7x, 8x, 9x, or 10x
  • Objective Lens Diameter: 30 to 42mm
  • Field of View: +350mm
  • Eye Relief: 15mm (if you wear glasses)
  • Focusing Mechanism: In natural location, moves smoothly
  • Type of Glass: Bak4 (barium crown or phosphate crown, depending on your budget), ED an additional luxury if you can afford it
  • Lens Coating: Fully-Multi-Coated w/Phase Coating
  • Proofing: Weather-Proof (with O-Rings) and Fog-Proof