Binocular Basics

Whether you are a bird watcher, wildlife enthusiast, sports or concert fanatic, hunter or you're just out site seeing, binoculars are the most important piece of equipment you can purchase.  Binoculars will allow you to examine birds closely and to see their field markings and color.  It will allow you to observe animal behavior and the natural habitats in which they live.  You can see your favorite player close-up or watch your favorite band as if you were in the front row.  Whatever your passion is, binoculars will bring you closer to the action and therefore afford you greater enjoyment of these activities.  However, before rushing out to buy yours, you should learn about some basic guidelines to help you purchase the right binoculars for you and your intended use.

 

There are many things you should consider when purchasing binoculars but probably the most important terms to understand are magnification and diameter.  The most common full-sized binocular would be 7x35mm.  The number before the “x” represents magnification.  The higher the number the closer the object will appear.  So using the most common binocular as our example, the image viewed will appear 7 times closer than with the naked eye.  The number after the “x” refers to the diameter (in millimeters) of the objective lens.  The objective lenses are those on the binocular that are the farthest from your face or the larger two.  The diameter of the objective lens gives the ability to gather light, which translates, into sharpness or clarity of the object viewed.  The larger the lens, the clearer or brighter the view will be. 

 

With both of these numbers, it is important to note that bigger is not always better.  For instance, higher magnification also magnifies unsteady hands resulting in an unsteady image.  It also results in a smaller field of view (only wide angle binoculars will provide a wider field of view), a darker image and a shallower depth of field.  And a larger diameter of the objective lens, the more glass required.  More glass means a heavier binocular.  This can be tiresome and make them more cumbersome to use, especially when trying to react quickly to a bird.  Most folks, especially birders, will use binoculars between 7x and 10x.  7x offers a very nice crisp and bright picture.  10x offers better performance over distance without compromising too much clarity.  8x is becoming popular since it offers a nice compromise of both.

 

Another key point to think about when choosing your binoculars is the type of coating on the lens.  By adding coatings to glass lenses, the amount of light reflected away from the lens can be reduces.  This will allow more light to enter in through the lens, which in turn will give you a brighter and clearer view.  You want to have a high quality coating or “multi-coating” to get the brightest image possible.

 

Good quality binoculars should have center focusing.  That is, there should be one central wheel that adjusts both barrels of the binoculars simultaneously.  There are also dioptic adjustments to adjust for the differences between the operator’s left and right eye on both eyepieces.  Bird watchers should watch for binoculars with the capability to focus down to 20 feet or less.  This will allow for better viewing under some circumstances in the field as well as in your backyard.

 

Although we have covered the basic things to consider, I would like to mention two more that are often talked about.  First is exit pupil.  Exit pupil refers to the magnified image in the eyepiece as it enters your eye.  The main importance of this is how it relates to the pupil size of your eye.  The pupil of the human eye changes in size from about 2mm to 8mm depending upon the existing light conditions.  Generally a 5mm exit pupil will provide enough brightness over many conditions but in low light conditions it will not provide enough light to see, as your own eye pupil may want to.  The result is a darker image and you may not see as much detail.  To calculate for exit pupil, you simply divide the magnification of the binocular into the diameter of the objective lens.  So, a 7x35mm binocular has an exit pupil diameter of 5mm (35 divided by 7).  A 10x50 binocular also has an exit pupil of 5mm (50 divided by 10). 

 

The last term I want to mention is eye relief.  Eye relief is the distance from the surface of the eyepiece at which the whole field of view is clearly visible.  Eye relief is especially important for eyeglass wearers.  Because they are already set 10-15 millimeters behind their corrective lenses, they require a binocular that offers a minimum of 15mm of eye relief.  This would also be helpful for people who would be wearing their sunglasses while using binoculars.

 

In closing, with this information you should be able to find binoculars that fit you.  Buying binoculars involves “trade offs”.  No one binocular will meet the needs of every situation.  It will require some compromises.  Just try to buy the best pair you can for what you can afford and soon you will be enjoying the rewards. 

 

To see our selection of binoculars click here:  Sheltered Wings Audubon Binoculars