Bird Watching Binoculars

How Do Binoculars Work?

1. Light moves through the objective lens (that's the lens furthers from your eye).
2. Then light travels through the prisms (prisms are inside the binocular barrels and manipulate light)
3. Light moves through the eye piece (that's the lens closest to your eye) which magnifies the image.
4. Light then reaches your eye.

Prism Types

For our purpose, we'll review the two major binocular designs:

1. The Porro Prism is characterized by the objective lens (that's the lens furthest from your eye) being spaced wider than the eyepiece.

2. The Roof Prism is characterized by the alignment of the eyepiece and objective lens.

Image Quality

Like all binoculars, many factors impact the quality of a bird watching binocular. Generally, the quality of the glass used (dense glass is better) and the type and number of anti-glare coatings greatly impacts clarity.

In the end, the numbers on a binocular are what your really need to know. Read on...

Numbers, Numbers --What Do They Mean?

8x42 (read as 8 by 42), 7.2 degrees (378 @ 1000 yards). Ik. All those numbers. Let's break it down.

1. The first number, 8, is the magnification--how many times larger the object will appear. This number varies--from about 4 to 12, with 8 and 10 being most common.

   Here is a rule-of-thumb

   As magnification increases, image clarity decreases. An unsteady hand makes this worse at higher level magnifications such as 10x or 12x. 7x or 8x is generally held as adequate for most bird watching binoculars, while 10x is a better choice for viewing long distances (for instance if you're bird watching over water).

2. The second number, 42 in this example, refers to the diameter of the objective lens (the lens furthest from your eyes) in millimeters. The objective lens can vary from 15mm to 50mm and beyond. The largest lenses normally require a tripod.

   The importance of the objective lens is directly related to light (the larger the lens, the greater the amount of light). However, the size of the lens will also determine the physical size of your bird watching binoculars (and the weight too).

   Here's another rule of thumb for you regarding your bird watching binoculars:

   If you use binoculars during the bright hours of day, or in well-lit areas, then an objective lens of about 25 is sufficient. If however, you want a brighter image or will be using your bird watching binocular at dusk or dawn, you'll want to choose a larger objective lens--say, around 35mm to 40mm.

3. Let's talk field of view, in our example 7.2 degrees (378 @ 1000 yards). This number refers to the widest dimension from left to right that you can see when looking through the binocular. It is expressed as either:

   1. A degree to indicate what "slice" you are seeing out of the 360 degrees scene surrounding you. In our example, the angular degrees is 7.2. Bird watching binoculars typcially fall within the 5 to 11 degree range.
   2. A number of feet @ a certain number of yards. In our example, we can see 378 feet wide when standing 1000 yards away from the object being viewed. Most bird watching binoculars fall with in the 250 to 600 feet range.

   A wider field of few is desirable for a couple of reasons:

   • It's easier to follow fast moving action
   • It's easier to find birds in denser backgrounds

   IMPORTANT NOTE: Field of view narrows as magnification increases (4x, 6x, 8x, 10x).

4. The exit pupil is the beam of light that exits each eyepiece of the binocular and enters the user's eyes. The larger the exit pupil, the brighter and clearer the image (especially under low light conditions).

   The exit pupil is measured in millimeters. Calculate it by dividing the objective lens by the magnification. For instance, a 10x42 binocular has a 4.2mm exit pupil (42 divided by 10 = 4.2).

There are other less critical, yet still important, specifications as well. Click here to learn about other bird watching binoculars specifications.

In the end, for the backyard, you should get either a:

• Compact binocular (one that is small and can fit into a pocket. Look for typical specs of 8x25. This is usually sufficient, but you will struggle to see at dawn and dusk.

• If you want a full-size backyard bird watching binocular, look for specs around 8x40 and 8x42. These will gather light better and show color at dusk and dawn.

  However, my final thought is that you may use the compacts more often due to their lighter weight and smaller size.
  
  
  I hope you found this article about bird watching binoculars useful. Click here for more great information about bird feeders and bird houses.