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Tuesday, February 21, 2006

Numbers Game

Did you ever look at your binoculars and wonder what the numbers on them mean? (Of course, if you’re math phobic, you’ve probably avoided looking at the numbers.)

Daisy, our Pembroke Welsh Corgi, is wondering about the numbers. Actually, more likely, she is wondering when she’ll get her next dog cookie. Binos for dogs, there’s an idea. We are working on a harness strap to hold them up for her.

Well, the numbers are your friend because they give you information about what you own. They are also a clue as to what makes the best kind of bino for birding. Usually the numbers say 8 x 42, 10 x 42, 7 x 35, 8 x 21 or something like that.

The first number is the power of magnification. So if the first number is 8, that means the image you are looking at will appear 8 times larger than it would if you were not using binoculars. All the better to see birds, such as this Royal Tern, up close. Makes sense.

The meaning of the next number, the 42, 35, 21, etc., is not so obvious. That number is the measurement, in millimeters, of the objective lens — the lens at the far end of your binocular. Usually, the larger the number, the bigger and heavier the lens and the more light the binocular will let in, producing a brighter image. The trick, however, is to not have the objective lens be so big and heavy that it would take King Kong to lug around the binoculars.

In general, good, all-purpose binoculars for general birding have a magnification of 8 and the objective lens is somewhere around 42. Some people (Lillian included) do use 10 power binoculars and they can be fine for birding, but the higher power magnifies hand shake. So don't try to withdraw from coffee while using them.

Today is the anniversary of the day we got Daisy 13 years ago. Daisy here is your cookie. Woof.

Photos of Royal Tern and Daisy Stokes © Lillian Stokes

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