Understanding Binocular Magnification

Magnifying Glass raised to the sky

Kate Ter Haar/Flickr/CC by 2.0

Good magnification is essential for birding binoculars to be useful and effective. Understanding binocular magnification can help birders choose the right binoculars for their eyes, budget and birding needs.

What Magnification Means

Binocular magnification is how much larger an object appears when viewed through binoculars compared to how large the same object would appear when viewed with the naked eye from the same distance. If binoculars have 8x magnification, for example, a bird will appear eight times larger through the binoculars than with plain eyesight. This allows birders to more closely observe birds and see details clearly from a greater distance, without approaching the birds and causing them distress or scaring them away.

Magnification is also sometimes called the "power" of the binoculars—binoculars labeled as 8-power have eight times magnification. Most optics have clearly labeled magnification, usually on the large focus wheel between the two long barrels of the binns. The binoculars' manual should also document the magnification.

Best Magnification for Birding

Binoculars can range from 6 to 12 magnification or even higher, but powers from to 10 are generally preferred for birding. There are pros and cons to both higher and lower magnifications, and birders should choose magnification based on what best meets their birding and eyesight needs.

  • Smaller magnification (6 to 7): Optics with smaller magnifications may be ideal for casual birders who are interested in binoculars primarily for the backyard or in easier habitats. Smaller magnification may not show very subtle field marks as clearly, but the binoculars are generally less expensive. When birds aren't too far away—such as approaching feeders—these smaller magnifications are ideal.
  • Larger magnification (10 to 12): Optics with larger magnifications can bring birds very close, but the field of view is smaller and may make locating birds more challenging. Faint shaking from the hands or wind will also seem much greater with larger magnifications. Birders who visit broad habitats, however, such as open fields, mountain ridges or large lakes, will appreciate the stronger power to see birds at greater distances.

Some binoculars offer zoom features with magnification ranging from 7 to 12 or greater on the same pair of binns. While this may seem to be the best option for all types of birding, the lower magnification typically offers the best view. The more the birds are magnified, the dimmer the overall view may be, making the zoom feature less useful. Zoom binoculars are also more expensive, and the cost may not be worthwhile for most birders.

Beyond Magnification

Magnification is undoubtedly one of the most important numbers to be aware of when purchasing and understanding binoculars. There are other numbers birders should consider, however, to find the best binoculars for their birding needs.

  • Lens width: This is the second number listed with magnification, and gives, in millimeters, the diameter of the binocular's lens. Binns labeled as 8x40, for example, have eight-power magnification and a 40-millimeter lens. The wider the lens, the brighter the image and the easier it will be to see fine field marks or color variations in birds' plumages.
  • Exit pupil: This number is not usually given, but is easy to calculate. The exit pupil is the small aperture closest to the eye and determines exactly how bright and clear images appear. Calculate the exit pupil size by dividing the lens width by the magnification—8x40 binoculars will have a 5-millimeter exit pupil. In comparison, 10x40 binoculars may have a greater magnification (10), but will only have a 4-millimeter exit pupil, which provides a dimmer, darker image.
  • Focus depth: This number, given in feet, describes how closely binoculars can focus. Ideally, birders should opt for a focus depth of 5 to 8 feet. A longer depth may make the optics impossible to use effectively at close range for observing backyard birds. This number has no impact on distance views, however, so binoculars with a shorter focus depth are still equally valuable to watch birds further away.
  • Weight: Most binoculars do not readily list weight, but how heavy they are can make a great deal of difference to comfort, particularly on long birding hikes. A heavier pair may be difficult to hold steady for long observations, and heavy optics can cause neck, shoulder or back pain. Using a binocular harness can help distribute the weight more evenly across the torso, but unsteady hands can have trouble with heavier binns. Testing out several types of binoculars can help birders choose a pair that has a comfortable weight.
  • Cost: The most critical number many birders consider is the cost of the binoculars. Prices can range from $20 to $2,000 or higher, and the general rule of thumb is to purchase the most expensive pair that fits within your budget. It is best to try several pairs of binoculars at a nature store, sporting goods outlet or another retailer to see what features are available at what prices. Then select the best possible model without paying for unnecessary bells and whistles that add to the cost but won't add to your birding.

Magnification is one of the most critical components of a good pair of birding binoculars. Understanding how magnification works and how it relates to other features such as lens width and exit pupil can help birders select the perfect pair of binoculars for all their bird watching.