Difficulty in identifying a bird is not always caused by poor optics.
By Karl Anderson
Difficulty in identifying a bird is not always caused by poor optics.
I've heard people say, in all seriousness, things like "I was out with Joe Xzzz and he identified a bird that was so far away that it was just a speck to me. I want to buy new binocs."
Hmmm, if you couldn't confirm the identification how do you know Joe was correct? But also remember that Joe has been studying birds for 40 years.
But suppose you really do need new binoculars? Or want to buy them as a gift? Consider the specifications, a number something like 8x30. The "8" is the "magnification," but it's more useful to think of it as the divisor of the distance between you and your subject.
A bird that's 40 feet away appears to be 5 feet away when viewed through an 8x glass, or 4 feet away through a 10x glass. Think about that. If a bird was actually 5 feet from you and it hopped a foot closer, would you really see it better? Probably not.
The moral: If all your birding is in the woods at relatively short distances, you might not need very high "magnification."
So why not have it anyhow? Well, that second number, the "30" is the diameter of the objective lens in millimeters. This determines the light-gathering power of the glass. If you increase the "magnification" without increasing the lens diameter, the image gets dimmer. Not noticeable at high noon on a sunny day, but perhaps at dawn or dusk.
And a bigger objective lens diameter generally means a larger and heavier binocular. And usually your close focus distance will increase. It's very frustrating to not be able to focus on a bird because you are too close, and can't back away because of the terrain.
How about field of view? That can be very important in finding a bird. You might think that it would increase if you increase the objective lens diameter. Not so. It is usually stated someplace, sometimes in meters or feet at some specified distance, sometimes in angles. The wider the better. An angular field of view of 6 degrees is about equal to a field 300 feet wide at a range of a thousand yards.
In all honesty, these comments apply mostly to mid-range binoculars. Very expensive binoculars bend the rules by using very high-quality optical glass and high-tech coatings to improve transmission of the light that passes though the 12 or more glass surfaces in a pair of binoculars.
What do I use? I have a pair of 8x32 binoculars that close focus to about 3 feet, which makes them good for looking at butterflies and lizards as well as birds. Field of view is 340 feet at a thousand yards. They weigh 18 ounces and they cost me about $350. I have a telescope for long-distance viewing of waterfowl and mammals.
For information about the Gloucester County Nature Club, see gcnatureclub.org/.
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