our Better Nature Home

The goal of this site is to provide you with useful, clear and accurate information about conservation and environmental protection.

printer friendly page
- by Stephanie Trementozzi

There are many different types and styles of binoculars, and it can be confusing when you are shopping for them.  However, if you will be using them mostly for birding, there are certain attributes that will help you choose what is best for you.

How heavy should they be?

Birdwatching.  Wikimedia Commons
Birdwatching in Central Park, NY. Wikimedia Commons photo

First of all, they should be lightweight.  You will be carrying them around your neck most of the day.   Also, if they are too heavy, you'll find that your hand will start to shake after you've held them for awhile.

What do the numbers mean?

There are two numbers that are part of the description of every pair of binoculars that you see, such as 8 X 32 or 10 X 42.  The first number is the degree of magnification in the binoculars.  If it is 8, then it means that the object you are looking at is 8 times larger than you can see with the naked eye.  This also determines the field of view.  The higher the magnification, the narrower the field of view will be.  Since birders are often looking at birds in flight, a wide field of view is an asset.  The second number is the diameter of the objective, or light gathering lens.  It is shown in millimeters.  The diameter of the lens determines how much light enters the binoculars.  However, as the lens diameter increases, the weight of the lens will also increase. 

What are the prisms for?

When light enters the end of the objective lens, the object you are looking at is upside down.  That light is sent to the prisms which turn the object right side up and send it to the eyepiece, which is the magnifying part of the binocular.  So three essential parts of the binoculars are the objective lens, the prisms and the eyepiece.

What does all this coating mean?

You will see in the description of the binoculars that they are either coated, multi-coated or fully multi-coated.  Without coating, light is reflected back and the object appears dim.  Here's what the different types of coating mean.

  • Coated:  A single layer of air to glass surface on some lens elements is coated.
  • Multi-Coated:  Some of the air to glass surfaces are coated by more than one coating.  Plastic surfaces cannot be coated.
  • Fully Multi-Coated:  All surfaces have received multiple layers of coating.

In the better roof prism binoculars, you will see the phrase "phase coated".  This is a coating applied to the roof prism to keep the light waves flowing through the lenses in sync.  Of course, the more coatings that are applied to the lens, the more the price goes up.  But remember, the more light that makes it through to your eye, the sharper and clearer the image will be.  This is especially important for birders who want to see clearly the markings on the birds to identify them correctly.

What is the exit pupil and why is it important?

The exit pupil refers to the amount of light that is allowed through the objective lens.  It reminds me of what an aperture does on a camera.  While the aperture on a camera can be adjusted to adapt to available light, the exit pupil is static and determined by the diameter of the objective lens.
This is important only if you are shooting in dim light.  This could be a common occurrence for birders because they are often out at dawn or dusk, or in shady areas with lots of trees.  In daylight, the average pupil is small, perhaps 4 or 5 mm.  However, when your light diminishes, the pupil in young adults expands to perhaps 7 mm.  However, as we age, our pupils expand to only 4 or 5 mm.   If the exit pupil is smaller than the diameter of your pupil, the amount of light that gets to your eyes is severely diminished.  You can determine the exit pupil by dividing the diameter by the magnification of the lens.

Are there other things I should look for?

There are several features that you need to think about.

  • Your binoculars should be 100% waterproof and fog proof.  You will be using them outdoors and you know you will be wet or at least damp at some point.
  • They should have eye relief for eyeglass wearers.  Because glasses hold the eye farther away from the eyepiece you need a longer cup.  However, the longer the cup, the less field of view you have.  Some binoculars have fold down eye cups, so your eyes are closer to the eyepiece.
  • A central focusing wheel is easier and quicker to use than a binoculars that requires you to focus each eye individually.
  • And last, but not least, they should be sturdy and rugged to handle any bumps they might encounter in the field.

There are many brands of binoculars to choose from but now that you have some knowledge of what to be looking for, your task should be easier.  Good luck!

Stephanie Trementozzi is the publisher of www.always-outdoors.com.   She resides in Culpeper, VA where she enjoys the great outdoors.

Related Our Better Nature articles: