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Binoculars: valuable tool for bird watchers

After bird watchers discuss all the birds they’ve seen, the next topic is their binoculars, a birder’s most valuable tool. If you wish to find a new pair for yourself with that Christmas bonus you’ve just received but don’t understand optics then read on.

The basic property of a binocular is the magnification or power, the common numbers are seven through ten. Thus a scene that is 200 feet away appears to be at a 25-foot distance when viewed by an eight-power magnifier.

The first surprise is bigger is not always better for several reasons. Most birders carry a seven to eight power binocular. They are usually lighter, and the image is less affected by shaking hands than the higher powers. The field of view is often larger, meaning that you can see a greater area with a lower power.



The next most important feature is the size of the objective lens, the lens furthest from your eye. There is a large range in objective size ranging from 25 mm to 50 mm and beyond. Again, a middle ground of roughly 40 mm is best. The larger the objective, the more light your binoculars gather and the greater the field of view.

However big lenses are heavy and expensive particularly when made from some or coated by the exotic materials. Light gathering ability is very important when one is trying to identify something like a Song Sparrow hidden in the underbrush.




The field of view, the size of the view,

is quoted as an angle or the diameter in yards of the scene viewed at 1,000 yards. A little trigonometry will convert between the two and is left as an exercise to the reader. The 1,000-yard measure is useless to birders who are mostly interested in much closer objects.

The minimum focal distance, the closest object that can be focused, is much more important to birding. The thing that is shaking some leaves may be a Huttons Vireo only six feet away. Here the smaller the better and low numbers run from five to 15 feet.

A heavy binocular will quickly fatigue the user leading to loss of acuity and enjoyment. Larger objective lenses will trade off against the weight and cost. A three-pound pair of binoculars on a thin strap can take all of the joy out of birding.

This brings us to the all important question of money or just how big was that bonus check. The authoritative review on the web (http://birds.cornell.edu/publications/livingbird/spring99/binos.html) by the Cornell Ornithology lab states, “In general, however, I recommend spending as much as you can afford on binoculars.”

The current top of the line favorites are the Brunton 7.5×43 Epochs, Nikon Venturer 8×42 LX and the Swarovski 8×56 SLC. That is the Brunton’s are eight power with a 43mm objective lens etc. Be prepared to spend around $1,500 for either of these.

Stephen Ingraham in his excellent web review (http://betterviewdesired.com) says, “At this price point ($900.), look at the Leica Ultra 8×32 (my current all around favorite birding glass). It is my opinion that for this kind of money you should get complete weatherproofness.”

Consumer Reports in their May 2002 issue chose the waterproof $150 Minolta Activa 8×40 as a “best buy.” Nonetheless, trying out binoculars at your local vendor is probably worth the extra cost to find an appropriate pair.

In Grass Valley Wildbirds Unlimited and in Nevada City The Nature Store have a small selection of medium-priced binoculars.

Walt Carnahan (photo on file) is the President of the Sierra Foothills Audubon Society and a retired Professor of Physics.


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