Binocular Selection Factors

If asked, most people would turn down help when selecting a pair of binoculars. Most likely, their predominent selection criteria is based upon either magnification or price. After all that is all there is to it, right?  Well...No. 

A few basic definitions to start. Binoculars are designated by their magnification and the objective lens diameter; for example 7x35 means that the binoculars will magnify an object so that it appears seven times (7x) closer than it actually is. The number 35 represents the diameter of the objective lenses in millimeters, which are the light gathering lenses. Exit pupil is a specification that defines the size, in millimeters, of the light at the eyepiece and should match the diameter of the iris for an unvignetted view. Exit pupil is more important factor when using the binoculars during low light periods. Eye relief is a measurement in millimeters of how far back from the eyepiece the eye should be positioned to enjoy a full clear view. This is an important specification for anyone that will be wearing eyeglasses. Eyecups are included to help position the eyes correctly. The system employed could be as simple as a rubber lip that rolls down or it could have adjustable cups that have twist up presets, which is much more desireable.  Field of View is a measurement of the width of the view at some standard distance downfield, typically at a thousand yards. Depth of View is the total distance into the field that is in focus.

When selecting binoculars, the first thing to consider is how you will be using them. Binoculars are used for birding, hunting, stadium events or even while day hiking scenic or nature trails. How will you use them? Consider if the binoculars will be used during the twilight of dawn or dusk, certainly a critical time period for hunters and birders alike. Binoculars with a larger objective lens (42-56mm) will help draw in more light during this time, however, at around 2 to 3 pounds; they will also be heavier if they will be carried around all day long. A binocular harness can help support the weight of full size binoculars without the fatigue associated with a neck strap. They support the binoculars at the chest when not in use and are reasonably priced. If a full day of lugging around heavier binoculars is not for you then by all means select a mid sized pair with an objective lens that is around 32 to 40 mm. Please keep in mind that the view may not be quite as bright as what the full size models can deliver. Do keep in mind though that higher quality glass in a smaller model can outperform lower quality glass in a larger model.

A binocular body style is based upon the type of prism that is utilized, either porro or roof. Porro prism binoculars are what we would define as the conventional style where the eyepieces are not in line with the objective lenses. Roof Prisms, on the other hand, do have the eyepiece and objective lenses in line. Roof prism binoculars are more compact and rugged than Porros but more costly to build. Some sources will cite that Porros will produce a brighter image and greater depth of field than roof prisms of the same magnification, objective size and optical glass quality. Roof prisms manufactured by Zeiss use a phase coating technique on the prism glass to produce truly remarkable image quality.

Do consider the ease of focusing. Quick focusing is a must for the hunter or the birder. Look for a pair of binoculars that can focus from close up out to infinity with a single stroke of the finger. You need to be able to zero in as quickly as you can so that you maximize the time analyzing the object so you don’t waste precious seconds messing around with the focus wheel. If eliminating the hassle of focusing is important to you, then consider a pair of binoculars that have a greater depth of field. Once the diopter adjustment is set, everything in the view is in focus, whether it is 50 feet away or 500 feet. This style is preferred by the military. Fujinon manufactures high quality binoculars that are "focus free" and also have options for a reticle or built in compass. The close focusing specification of a binocular designates how close to the user the binoculars will focus. Every binocular focuses out at infinity but close focus specification are different for each model. Brunton and Zeiss have models with close focus specifications of three to six feet respectively. The close focus is a critical specification for birders and those who enjoy butterfly watching. If close focusing is important to you, then select a pair that has a specification of ten feet or less.

The next thing to consider is the lens coatings. Coated optics help to reduce light that get reflected within the binocular housing. As more light gets reflected rather than transmitted the result is a view with a reduced contrast of the scene or object.Fully multi coated lenses are most desireable. Be careful here as there are also other coating designations as well.
Coated optics- A single layer on at least one lens surface.
Fully coated optics- A single layer on all air to glass surfaces.
Multi coated optics have multiple layers on at least one lens surface.
Fully multi coated optics have multiple layers on all air to glass surfaces.

What is the likelyhood that you will need to depend upon your binoculars during a rainstorm? Most all of us, when in the field, want to make the most of the opportunity and generally don't let rain get in our way. Unfortunately just like any glass surface, the view may get distorted due to the moisture build up on the glass lenses. Once again this could be a time when seconds matter and stopping to wipe the lenses could result in a lost opportunity or perhaps even scratched lenses if you do not have a soft lens cloth along. Zeiss has an additional proprietary coating called Lotutec coating which actually causes water to bead up and roll of the lenses allowing continued use during a rain. Lotutec coating truly provides a lot of value for the serious hunter or birder.

Now let’s talk more about magnification. When you look through a pair of binoculars your observing the field of view. As magnification is increased, the results are reduced eye relief and a narrower field of view. In addition, as a larger magnification is selected it is more difficult to hold the binoculars steady enough by hand without getting movement. Additionally, in maritime use where the continuous bobbing and rolling produced by the water also creates motion, a smaller magnification and larger objective lens size will allow for more forgiveness for the movement. So select magnification carefully, as 7x or 8x powers will work fine for most applications. If higher magnifications are needed for land applications, then consider purchasing a support such as a tripod. Image stabilized binoculars are ideal for maritime use.

Finally, color and clarity of the view is the most important feature that differentiates premium binoculars from less expensive binoculars. Serious hunters and birding enthusiasts alike demand these quality features. Having a view that allows you to pick out detail and colors from a camouflaged background can mean the difference between spotting the object of interest and missing it completely.

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