Binocular Magnification

Understanding Magnification for Birding Binoculars

Magnifying Glass
Do your binoculars use the best magnification?. Jeffrey Beall

Good magnification is essential for birding binoculars to be useful, and 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. 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 barrels of the binns. The binoculars' manual should also document the magnification.

Best Magnification for Birding

Binoculars can range from 6-12 magnification or even higher, but powers from 8-10 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 needs.

  • Smaller Magnification (6-7): Optics with smaller magnifications may be ideal for casual birders who are interested in binoculars primarily for the backyard. Smaller magnification may not show very subtle field marks as clearly, but the binoculars are generally less expensive.
     
  • Larger Magnification (10-12): Optics with larger magnifications can bring birds very close, but the field of view is smaller and that may make locating birds more challenging. Faint shaking from the hands or wind will also seem much greater with larger magnifications.

Some binoculars offer zoom features with magnification ranging from 7-12 or greater on the same pair of binns.

While this may seem to be the best option, the lower magnification typically offers the best view, and 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

While magnification is one of the most important numbers to be aware of when purchasing binoculars, there are other numbers birders should consider 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-millemeter lens. The wider the lens, the brighter the image and the easier it will be to see fine field marks or color variations.
     
  • 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 5-8 feet, because a longer depth may make the optics impossible to use effectively at close range for observing backyard birds.
     
  • 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 or back pain. Using a binocular harness can help distribute the weight more easily across the shoulders, but unsteady hands can have trouble with heavier binns.
     
  • 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 other retailer to see what features are available at what prices, and select the best possible model without paying for unnecessary bells and whistles.

Magnification is one of the most critical components of a good pair of birding binoculars, and 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 binns for all their bird watching.

Photo – Magnifying Glass © Jeffrey Beall